RU2606369C1 - System of measuring concentration of boric acid in power nuclear reactor heat carrier circuit - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to measurement equipment, in particular to systems for continuous and real-time measuring the concentration of boric acid in the first circuit of a nuclear reactor heat carrier. System of measuring the concentration of boric acid in the power nuclear reactor heat carrier circuit includes the first and the second laser generators, the measuring and the reference cuvettes, the first and the second photodetector units electrically connected to the processing and control unit, as well as optical elements providing optical connection between the laser generators, the cuvettes and the photodetector units. Measurement is performed as per the absorption spectral method by illumination with a probing laser radiation of the measuring cuvette connected to the first circuit of heat carrier of a nuclear VVER-reactor.

EFFECT: technical result of the invention is higher accuracy of measurements, as well as the possibility of measuring low concentrations of boric acid in the heat carrier and providing real-time remote measurements.

7 cl, 9 dwg, 2 tbl

Description

The invention relates to the field of measuring equipment and nuclear energy and is intended for use in a nuclear power reactor of a nuclear power plant for continuous monitoring and operational measurement of the concentration of boric acid in the coolant of a VVER-type nuclear reactor. Boric acid, contained in the form of an aqueous solution in the coolant circuit, contains a chemical element Bor-10, the atomic nucleus of which is an effective absorber of neutrons generated during the operation of a nuclear reactor. The concentration of Boron-10 atoms in the composition of the coolant is a factor determining the operating mode of a nuclear reactor. At the same time, a change in the concentration of boron atoms in the coolant is used to change the operating mode and control a nuclear reactor. By changing the concentration of boron atoms in the coolant, regulation and compensation of the burning of fuel rods (fuel rods) in the operating mode of a nuclear reactor is carried out. This is due to the fact that the degree of neutron absorption depends on the concentration of boron atoms in the coolant. The resulting neutrons due to the presence of boron atoms in the coolant are switched off from the chain reaction. The uneven distribution of generated power arising from the use of standard control mechanical elements in a nuclear reactor is eliminated. Therefore, an accurate and operational measurement of the concentration of boron atoms in the composition of the coolant in the primary circuit and slave circuits is necessary to effectively control the operation of a nuclear reactor and increase the safety of nuclear power plants. The boric acid molecule H ₃ BO ₃ contains one Boron-10 atom. Therefore, measuring the concentration of boric acid in the coolant circuit of a nuclear reactor is equivalent to measuring the concentration of Boron-10 atoms. There are various methods for measuring the concentration of boric acid in its aqueous solutions, used in various sectors of the economy. In nuclear energy, the main method for measuring the concentration of boric acid in the coolant circuit is the chemical measurement method [1], based on taking a sample of the coolant substance directly from the coolant circuit using a special device for sampling from the main primary coolant circuit directly in the operating mode of a nuclear reactor [20] ]. Further, the obtained sample of the coolant substance in special laboratory conditions that provide protection against radiation is exposed to a number of chemicals that cause luminescence of the test substance of the sample. The concentration level of boric acid is determined by the luminescence intensity of the processed sample substance from the coolant circuit. The disadvantages of this method for determining the concentration of boric acid in the coolant circuit include low accuracy, especially when determining low concentrations of boric acid, due to the influence of various factors when processing a sample with a set of special substances that excite luminescence when interacting with a solution of boric acid. A significant drawback of this method is the danger of radiation damage to which nuclear power plant personnel are exposed when transporting the sample to the laboratory compartment and when processing and measuring the parameters of the obtained sample substance. This method is also characterized by low efficiency, since the transportation and processing of the sample takes a considerable amount of time and does not allow you to quickly and repeatedly receive information about the parameters of the coolant in the circuit of a nuclear reactor.

Known radiation methods for determining the concentration of boron atoms in the composition of the coolant in the circuit of a nuclear reactor [2], [3], [7]. These methods are based on direct measurement of the parameters of the neutron flux at the outlet of a nuclear reactor, or they use the measurement of the absorption of the neutron flux when the coolant is irradiated with a neutron source. The first method is characterized by low accuracy and low sensitivity and allows the measurement of only large concentrations of boron atoms in the composition of the coolant. The second method, implemented in the device [7] according to the RF patent, uses irradiation of the coolant with an external neutron radiation source and measurement of the neutron absorption level using a special measuring device. In this case, the measuring device and the neutron source are installed on the existing pipeline of the coolant circuit of a nuclear reactor. The irradiating measuring neutron flux passes perpendicular to the pipeline and the flowing medium of the coolant and captures a small part of its volume. As a result, the accuracy of determining the concentration of boron atoms is not high, especially when determining low concentrations of boron in the composition of the coolant. It should be noted as disadvantages the great complexity of installation and maintenance of radiation measurement equipment, which is located directly on the elements of the pipelines of the coolant circuit in the radiation area. In these methods, it is not possible to control the technical condition of radiation measuring equipment, which significantly reduces the reliability and reliability of the information received. Thus, the currently known methods for measuring the concentration of boron atoms in the coolant in the circuit of a nuclear reactor are characterized by low accuracy, great difficulty in maintenance in radiation conditions during the operation of a nuclear reactor, and the danger of radiation damage to the personnel of nuclear power plants.

The most accurate method for determining the concentration of boron atoms in an aqueous solution of boric acid is an optical photometric measurement method. The application of this method is based on direct photometry and measurement of the luminous flux of the corresponding wavelength transmitted through the coolant material of the cooling circuit of a nuclear reactor. To implement this measurement method, it is necessary to insert a measuring flowing optical cuvette with optically transparent windows-portholes directly into the coolant circuit of a nuclear reactor through a bypass pipeline. A second embodiment of the photometric method for measuring the concentration of boric acid in the composition of the coolant of a nuclear reactor circuit is possible, which does not require the insertion of a flow measuring cell directly into the coolant circuit. According to this option, the measured working substance from the coolant circuit of the nuclear reactor is fed into the measuring cell with transparent windows through a special additional pipe (branch) from the outlet of the sampling device of the nuclear reactor, which exists and is used in the nuclear reactor to obtain a sample of the coolant substance and use this sample in the considered above the chemical method for determining the concentration of boric acid in the coolant circuit of a nuclear reactor. In this case, the coolant substance is supplied to the measuring optical cell through an additional pipeline by means of an automatic remote-controlled valve. After measuring the concentration of boron in the optical measuring cell, the coolant is drained from this measuring cell into a special tank for further disposal using a second outlet remote-controlled valve. Thus, the filling of the measuring optical cell with the coolant from the nuclear reactor loop is carried out without contact of the NPP personnel with the measuring equipment and the obtained sample material. At the same time, a special direct connection (insert) of a measuring optical cell to the coolant circuit is not required.

Measurements of the concentration of substances in a gas or water medium by the photometric method are known and are successfully applied in various technical fields. However, the application of this method in nuclear energy presents certain technical requirements for the equipment and requires the solution of a number of complex problems and tasks. It should be noted the impossibility of placing the equipment near the working zone of the reactor and the need to remove the measuring equipment from the radiation exposure zone and its location at a considerable distance from the measuring cell, the requirement for high accuracy in measuring very low concentrations of boric acid (about 0.5 mg / l of coolant) in the end of the working session of the nuclear reactor, ensuring high reliability and confidence of the measurement results, as well as the requirement of high operational sti in carrying out measurements. The presented invention is aimed at solving these problems.

Known devices that implement the photometric method for measuring the concentration of substances contain a radiation source, a photodetector, a measuring cell, with which the measuring and reference measurement channels are formed, a measurement processing circuit. The disadvantage of these devices is the relatively low measurement accuracy, especially manifested at a low concentration of the measured substances due to the low absorption capacity of the measured substance. To overcome this drawback, an increase in the length of the measuring cell is usually carried out, or a multi-pass cell is used. However, these methods of increasing accuracy are not applicable for measurements in a nuclear reactor. Known two-beam photometer with a multi-pass cell [4] according to the patent of England No. 1157086. The device contains a radiation source, measuring and comparative channels (cuvettes), a mirror modulator, a photodetector, a signal conversion unit. The disadvantages of the device include the low accuracy of measurements.

A device [5] according to the patent of the Russian Federation No. 2022239, designed for optical absorption analysis of a gas mixture. The device contains an infrared radiation source, a broadband filter, a measuring cell, an interference filter, a photodetector filled with nitrous oxide. The disadvantages of this device include the low accuracy of the measurement, which is due to the instability of the parameters of the source of infrared radiation and the radiation receiver and the inability to compensate for this instability. As a prototype, the device closest in technical essence to the patent of the Russian Federation No. 750287 [6] was selected. The device is a two-beam photometer and is intended for optical absorption analysis and determination of concentrations of substances in the liquid phase. This device contains a radiation source with a condenser, a multi-pass (two-pass) cuvette with the test substance, a measuring and comparative channels, an interference filter, two photodetectors, a mirror mechanical modulator, a differential cascade, a signal processing and control unit. The disadvantages of this device include the low measurement accuracy, especially manifested when measuring low concentrations of substances. This is due to the impossibility of increasing the length of the measuring cell when measuring low concentrations of the substance, as well as the influence of the spread in sensitivity of the two photodetectors used and the lack of compensation for this spread. It should also be noted the fundamental impossibility of using a measuring optical device created according to this scheme for measurements in an operating nuclear reactor. This is due to a number of specific requirements for equipment for measuring the parameters of the coolant in the primary circuit of a nuclear reactor. Such requirements and current factors include the impossibility of measuring equipment being located near a nuclear reactor and the need to transfer the equipment to a separate room protected from radiation at a considerable distance from the reactor - about 50-100 meters, as well as the impossibility of increasing the length of the measuring cell over one meter and the inability to use multi-way cuvette with increased dimensions (in diameter) and requiring periodic maintenance by technical personnel.

The aim of the invention is to overcome these drawbacks and create a measuring system for optical absorption analysis and continuous remote measurement of boric acid concentration in the primary circuit of the coolant of a WWER-type nuclear reactor with high accuracy, which ensures the measurement of low concentrations of boric acid. Measurement of the parameters of the primary coolant of a nuclear reactor is carried out remotely in an automatic mode and with high efficiency, without the participation of maintenance personnel who are not exposed to any radiation hazard. The proposed measuring system provides the ability to measure with high accuracy large concentrations of boric acid in the composition of the coolant of the order of tens of grams per liter of coolant at the beginning of the working session of a nuclear reactor, as well as the measurement of small concentrations of boric acid in the composition of the coolant of the order of 0.5-0.1 mg / l at the end of a working session of a nuclear reactor. This is realized through the use of special tools that provide multiple passage of the measuring probe laser radiation through a measuring cell with limited dimensions that can be used in a nuclear reactor. At the same time, only a measuring cell is located near the nuclear reactor, which is connected via a fiber-optic line to the main measuring equipment of the measurement system, which is located in a separate room that is safe in radiation terms.

Achievable technical result is an increase in the accuracy of measuring the concentration of boric acid in the primary circuit of the coolant of a nuclear reactor, the implementation of measurements of small concentrations of boric acid in the composition of the coolant, ensuring high efficiency of measurements remotely at a considerable distance from the existing nuclear reactor without the participation of maintenance personnel.

The specified technical result is achieved as follows.

1. In the system for measuring the concentration of boric acid in the coolant circuit of an energy nuclear reactor containing a first laser generator, a measuring and reference cell, electrically coupled to the first photodetector unit and the processing and control unit, the second photodetector unit, the output of which is connected to the processing and control unit, controlling the input of the first laser generator is connected to the processing and control unit, the second laser generator, the third photodetector unit, the first and second laser radiation modulators are introduced I, four controlled attenuators, two remote mirrors with control units, sequentially mounted on the optical axis of the measuring cell, optically coupled to the first corner reflector, the first beam splitter, the optical output of which is connected to the optical input of the measuring cell, the second corner reflector, optically connected to the optical output of the measuring cell optically coupled third angular reflector, second beam splitter, optical output, sequentially mounted on the optical axis of the reference cell One of which is connected to the optical input of the reference cell, the fourth corner reflector, optically coupled to the optical output of the reference cell, optically coupled to the first fiber adapter, a fiber optic line and a second fiber adapter, the optical output of which is connected to the optical input of the first beam splitter, and four reflective mirrors and four translucent mirrors, wherein the output of the first laser generator through the first reflective mirror is connected to the optical input of the first laser modulator radiation, the output of the second laser generator through a third translucent mirror is connected to the optical input of the first laser modulator, the optical output of which through the first translucent mirror is connected to the optical input of the first fiber adapter when the first remote mirror is output, the optical output of the first laser radiation modulator when the first remote the mirror is optically connected to the optical input of the second controlled attenuator, the output of which by means of a fourth reflectively of the mirror is connected to the optical input of the second beam splitter, the optical input of the first fiber adapter when the first and second remote mirrors are pulled out is optically connected through the first translucent mirror and through the fourth translucent mirror to the optical input of the second laser modulator and to the optical input of the fourth controlled attenuator, the optical output of which connected to the optical input of the second photodetector unit, the optical output of the second laser radiation modulator is optically connected to the optical the input of the first photodetector block, the optical output of the first laser modulator through the first translucent mirror and through the second translucent mirror is optically connected to the optical input of the first controlled attenuator, the output of which is connected to the optical input of the third photodetector, the optical output of the first laser modulator by the first and second translucent mirrors, second and third reflective mirrors and through a third controllable attenuator, by means of a second optical mirror in the entered state and through the fourth translucent mirror is optically connected to the optical inputs of the second laser radiation modulator and the fourth controlled attenuator, the optical input of the second controlled attenuator when the first remote mirror is inserted and the second remote mirror is brought out is optically connected through the first remote mirror, the first translucent mirror and the fourth translucent mirror with an optical input of the second laser radiation modulator and with an optical input h tver controlled attenuator, the control inputs of the second laser generator, the first and second laser radiation modulators, the first, second, third and fourth controlled attenuators are connected to the processing and control unit, the control units of the first and second remote mirrors are connected to the processing and control unit, the output of the third photodetector unit is connected to the processing and control unit.

2. The measurement system according to claim 1, characterized in that it uses a laser generator of the ultraviolet wavelength range as the first laser generator.

3. The measurement system according to paragraph 1, characterized in that the first and second laser generators are configured to tune the wavelength of the generated laser radiation.

4. The measurement system according to claim 1, characterized in that an acousto-optic cell with a control unit connected to the processing and control unit is used as a beam splitter, the optical input of the acousto-optical cell being optically coupled to the optical input of the measuring cell and the optical output of the acousto-optical cell being parallel optically connected to the first corner reflector and the optical output of the second fiber adapter.

5. The measurement system according to claim 1, characterized in that the reference cuvette is equipped with a working substance filling unit, equipped with inlet and outlet taps.

In FIG. 1 is a block diagram of a system for measuring the concentration of boric acid in a coolant circuit of a nuclear power reactor. The numbers in FIG. 1, the following elements are indicated.

1 - the first laser generator.

2 - measuring cell with optical windows transparent to laser radiation.

3 - reference cell, which is an analogue of a measuring cell.

4 - the first photodetector unit.

5 - the second photodetector unit.

6 - processing and control unit.

Next, the numbers indicate the newly entered elements.

7 - the second laser generator.

8 - the third photodetector unit.

9 - the second modulator of laser radiation.

10 - the first modulator of laser radiation.

11, 12, 13 and 14 - the first, second, third and fourth corner reflectors.

15 - fiber optic line.

16, 17 - the first and second fiber adapters.

18 - the first beam splitter, which is used as a translucent mirror.

19 - the second beam splitter, which is used as a translucent mirror.

20 is a first remote mirror with a control unit 21, shown in the withdrawn state. In the entered state, the mirror 20 takes position 37.

21 is a second remote mirror with a control unit 23, shown in the withdrawn state. In the entered state, the mirror 22 is in position 36.

24, 25, 26 and 27 - the first, second, third and fourth controlled attenuators.

28, 29, 30 and 31 - the first, second, third and fourth reflective mirrors.

32, 33, 34 and 35 - the first, second, third and fourth translucent mirrors.

38 - block filling the reference cell 3 with a working substance.

49, 50 - nozzles for connecting the measuring cell 2 to the coolant circuit of a nuclear reactor.

Remote mirrors 20 and 22 perform their technical functions only in the entered state in the optical circuit. This entered state in the optical circuit is indicated by the positions 37 for the first extension mirror 20 and the position 36 for the second extension mirror 22. FIG. 1 shows the main working position of the remote mirrors - the position in the withdrawn state from the optical circuit. In this operating state, a measuring cell 2 is connected to the optical measuring circuit, in which the concentration of boric acid is measured. When the state of the first remote mirror 20, which is set at position 37, is entered, a reference cell 3 is connected to the optical measuring circuit, in which the concentration of boric acid in the working substance of the reference cell 3 is measured. In this case, the second remote mirror 22 is in the withdrawn state. When the state of the second remote mirror 22, which is set at position 36, is entered, the photodetector blocks 4, 5, and 8 are calibrated together. The optical measuring circuit consists of laser generators, photodetector blocks, two laser radiation modulators, and four controlled attenuators, as well as reflective and translucent mirrors.

In FIG. 2 shows a second variant of connecting the fiber optic line 15 through the fiber adapter 17 to the optical input of the measuring cell 2. The designations of the elements correspond to FIG. one.

In FIG. Figure 3 shows the third option for connecting the fiber optic line 15 through the fiber adapter 17 to the optical input of the measuring cell 2. In this embodiment, the first corner reflector is excluded, the functions of which are performed by the first beam splitter 18, which, as in previous versions, uses a translucent mirror. The designations of the elements correspond to FIG. one.

In FIG. 4 shows an embodiment of the use of an acousto-optic cell 39 as a beam splitter 18. The numbers in FIG. 3, the old elements corresponding to FIG. 1, and new items:

39 - acousto-optical cell.

40 - control unit acousto-optical cell.

41 - piezoelectric element.

In FIG. 5 shows a block diagram of the connection of the measuring cell 2 to the output of the sampling device in the first coolant circuit of the nuclear reactor, where the numbers indicate the following elements:

42 - pipeline of the primary coolant of a nuclear reactor.

43 is a device for sampling from the primary coolant of a nuclear reactor.

44, 45, 46 - controlled valves.

47 - drain operated valve.

48 - container for collecting waste coolant.

The remaining elements correspond to FIG. one.

In FIG. 6 shows a sequence of reverse laser pulses recorded by the first 4 and second 5 photodetector units shown in FIG. one.

In FIG. 7, FIG. 8 and FIG. Figure 9 presents the results of modeling the operation of the measuring system during measurements with various levels of boric acid concentration. The measurements are presented in the form of a sequence of recorded reverse pulses of laser radiation at various levels of boric acid concentration C in the composition of the coolant in the cooling circuit of a nuclear reactor.

The principle of operation of the proposed system for measuring the concentration of boric acid in the coolant circuit is as follows. The measuring system (Fig. 1) works as follows.

The system continuously measures the optical parameters of the coolant substance directly in the primary coolant circuit of a nuclear reactor. The measurement of optical parameters is carried out by the absorption-spectral method, by transmitting laser radiation (LI) generated by the first laser generator pos. 1 (see Fig. 1) through a measuring cell 2 and then measuring the optical parameters of the laser radiation transmitted through the cell 2 using the first photodetector unit 4, as well as using the second photodetector unit 5. Measuring cell 2 using special pipes 49 and 50 is connected to the first circuit of the coolant of a nuclear reactor by means of a bypass (bypass pipe). This ensures that the volume of the measuring cell 2 is filled with the substance of the coolant circulating in the primary coolant of the nuclear reactor. Measuring cell 2 is equipped with special optical windows transparent for laser radiation of laser generators pos. 1 and 7. The measuring cell 2 is located near the nuclear reactor in the radiation area and is connected to the rest of the measuring equipment located in the absence of radiation, fiber optic line 15, having a length of about 50-100 meters. Thus, using a measuring cuvette 2, located separately from the measuring equipment, the optical parameters of the coolant are measured directly in the primary coolant of the nuclear reactor. In the measurement system, the first laser generator pos. 1 is the main source of probing laser radiation, at a wavelength of which the optical transmission characteristics of the probing laser radiation are measured with the studied coolant substance - boric acid solution. In accordance with the characteristics of optical absorption of radiation by boric acid, a laser of the ultraviolet wavelength range is used as the first laser generator 1. The second laser generator 7 is an auxiliary generator and generates laser radiation in the longer wavelength region of the spectrum. Using this laser radiation, the measurement system is monitored and tested, and the optical transmission parameters of the measuring and reference cuvettes are parallel tuned. The reference cuvette 3 is a complete analogue of the measuring cuvette 2. The reference cuvette 3 is filled with a filling unit 38 with a reference working substance, which is a boric acid solution with a known concentration, or distilled water. This allows you to fine-tune and calibrate the measurement system using the well-known parameters of the reference solution of boric acid contained in the reference cell 3.

The absorption-spectral method is based on the determination of the absorption of optical radiation of a certain wavelength when it passes through the test substance - the coolant in the circuit of a nuclear reactor. When using this method, also called the photometric method, a measurement is made of the level of laser radiation of the corresponding wavelength, I ₀ , supplied to the optical input of the measuring cell 2, and also a measurement of the level of the amount of laser radiation I passed through the measuring cell pos. 2. After measuring and recording the two indicated values of laser radiation, the concentration C of boric acid in the composition of the coolant is determined by the following formula:

where V is the value by which the light flux decreases when passing through the layer of the investigated substance with a thickness (length) L: V = I ₀ -I; K is the extinction coefficient of boric acid (a parameter characterizing the ability of boric acid to absorb optical radiation of a certain wavelength). Dimension K - l / g cm. Dimension C - g / l.

Formula (1) is the main one for determining the concentration of substance C in the absorption spectral method and is well known in the technical literature. In the proposed measuring system, this ratio is used to measure relatively large and medium concentrations of boric acid in the composition of the coolant of a nuclear reactor - ranging from tens of grams per liter at the beginning of a session of a nuclear reactor to tens of milligrams per liter of volume of coolant in the middle and end of the session period work. To measure small concentrations of the order of tenths of a milligram per liter (mg / l), a special measurement mode is used, which is discussed below. It should be noted that boric acid, which is present in the coolant as an aqueous solution, is characterized by a very small absorption of optical radiation and, accordingly, a small extinction coefficient K. A noticeable absorption of optical radiation by boric acid takes place in the ultraviolet wavelength range of 200-400 nanometers However, even in this range, the absorption of radiation by boric acid is very small and requires special measures to increase the sensitivity of the absorption spectrum. cial method for measuring low concentrations of boric acid values required in monitoring and controlling the operation of the nuclear power reactor.

It should be noted that the quantity (product) KL in formula (1) determines the sensitivity of the absorption spectral measurement method. Indeed, the main technically measurable quantity is the value V in (1), which is determined and caused by a decrease in the level of luminous flux after passing through the measuring cell, compared with the level of light flux at the entrance to the measuring cell. The measurement of the parameters of the light flux (pulse of the probe laser radiation) after passing through the layer of the investigated substance is the main operation of the absorption spectral method. The main measured parameter here is the ratio P _ISM = V / I ₀ , which is further used in relation (1) to directly determine the concentration of boric acid or other substances measured by this method. To ensure a sufficiently high accuracy of measurements of the levels of light fluxes using modern equipment, the ratio P _ism must exceed a certain threshold level for measuring small values in the specified equipment. For modern measuring equipment, this level is of the order of 1%, hence the value of the recorded relative decrease in luminous flux P _ISM = V / I ₀ should be not less than 0.01: P _ISM > 0.01. Thus, when performing measurements by the absorption-spectral method in order to obtain the high required measurement accuracy, the relative value Р _{ism of the} decrease in the luminous flux should be not less than one percent of the luminous flux arriving at the input of the measuring cell and satisfy the relation

It can be argued that the ratio _Pmr = 0.01 determines the threshold value of the minimum concentration of boric acid, which can be measured at a given known extinction value K at the optical radiation wavelength selected for measurements.

The basic equation relating the incident and transmitted light fluxes and the concentration of the test substance C can be represented in the following form:

where the following values and dimensions were used: L [cm] - layer thickness of the test substance (length of the measuring cell), C [mg / l] - concentration of boric acid, K - extinction coefficient.

According to relations (2) and (3), the minimum measured concentration C _min is equal to the following value, determined from the equation

Expanding in a series the exponential for small values of K and C, we obtain for C _min :

The value of C _min in (5) determines the minimum possible measured concentration of boric acid and is the sensitivity of the (potential) absorption spectral method and, at the same time, the sensitivity of the equipment used for measurements. At the same time, this value characterizes the accuracy of the measurements, since it determines the minimum recorded gradation of the change in the concentration C of boric acid in the composition of the studied coolant substance. From (5) it follows that the sensitivity of the method is determined by the product of the KL values and increases (in the sense of decreasing the minimum recorded value C _min ) with increasing product KL. Boric acid is characterized by a very small extinction value (K << 1 log ^-1 ⋅ cm ^-1 ), which, according to (5), significantly increases the minimum recorded concentration of boric acid and, accordingly, leads to a deterioration in the sensitivity of the used measuring equipment. Therefore, when making measurements of low concentrations of boric acid, the problem of increasing the sensitivity of measuring equipment, the solution of which is proposed in the present invention, arises. The standard absorption spectral method allows measurements of relatively high concentrations of boric acid. So, for example, according to formula (5), when the length of the measuring cell is L = 1 m, the extinction coefficient of boric acid is K = 0.164 at the shortest wavelength of modern laser generators of the UV range of the order of 220 nm and the value of _Pm = 0.01, we obtain the minimum value the measured concentration of boric acid (sensitivity of the measurement system) C _min = 0.6 mg / l of coolant.

The measurement of large and medium concentrations of boric acid in the composition of the coolant of a nuclear reactor circulating through a measuring cell 2 is carried out as follows.

The laser generator 1 is the main one and generates laser radiation (LI) in the ultraviolet region of the spectrum, in which boric acid has the highest absorption capacity, i.e. extinction coefficient K is of the greatest importance. Second laser generator pos. 7 performs additional functions of monitoring and setting the operating mode of the measurement system. The laser generator 7 generates laser radiation in the blue or green region of the visible spectrum, in which the absorption of optical radiation by boric acid is practically absent, which allows using this laser radiation from the laser generator 7 to jointly configure and test a measuring 2 and reference 3 cell. Laser generators 1 and 7 operate separately. The laser radiation modulator 10 performs the formation of pulses of probe laser radiation of a certain duration from the laser radiation from the first 1 or second 7 laser generators operating separately. In this case, the laser radiation generated by the first laser generator 1, from its optical output enters the optical input of the first modulator LI 10 after reflection from the first reflective mirror 28 and through the third translucent mirror 34. In this case, when the first laser generator 1 is in operation, the second laser generator 7 is in the off state, and vice versa, the first laser generator is turned off during the operation of the second laser generator 7, the laser radiation from the output of which goes to the input of the first modulator LI 10 through the third floor transparent mirror 34. The proposed measuring system provides for the use of laser generators 1 and 7 of continuous radiation. In this case, the formation of pulses of LI short duration is carried out by the first modulator of laser radiation 10 by the control signals from the processing and control unit 6. It is possible to use modern laser generators of the visible and ultraviolet ranges, generating pulses of laser radiation of nanosecond duration. In this case, the laser modulator 10 operates as a controlled attenuator of transmitted laser radiation. The composition of the laser generators 1 and 7 includes blocks for the optical formation of the output beam. The repetition rate of 10 LI pulses generated in the LI modulator is of the order of one hertz. A higher repetition rate is not required, since the concentration of boric acid in the coolant flowing through the measuring cell 2 is determined from one generated pulse of the probe laser radiation. Concentration C is the main measured parameter of the measuring system. The generated pulse of the probe laser radiation from the output of the laser modulator 10 is fed to the input of the fiber adapter 16 of the fiber optic line 15 through the first translucent mirror 32. In this case, the first remote mirror 20 is in the withdrawn state, as shown in FIG. 1. It should be noted that in the operating mode of measuring concentration C in the measuring cell 2, the first 20 and second 22 remote mirrors are in the withdrawn state, as shown in FIG. 1. When making measurements using a reference cuvette 3, the first remote mirror 20 is transferred to the entered state using the control unit 21 and occupies the position shown at 37 in FIG. 1. In this case, the remote mirror 22 remains in the same position. In the calibration and functional control mode, the second remote mirror 22 is put into the entered state, indicated by 36 in FIG. 1. In this case, the first remote mirror 20 may be in either of the two indicated states. The fiber adapter 16 is necessary for introducing laser radiation into the fiber optic line 15 and for matching the parameters of the latter with free space. Then the laser radiation enters the fiber optic line 15, propagates in it to the second fiber adapter 17 and from its output goes to the input of the first beam splitter 18, which is used as a translucent mirror. Next, the probe laser pulse after reflection from a translucent mirror (beam splitter) 18 propagates along the optical axis and enters the measuring cell 2. The beam splitter 18 in the form of a translucent mirror separates the light flux coming from the left exit (end) of the measuring cell 2 into two light fluxes arriving at the corner reflector 11 and at the input of the fiber adapter 17. In the reverse stroke, the beam splitter 11 directs the light flux coming from the corner reflector 11 and from the fiber adapter 17 to optical input (left end) of the measuring cell 2. Thus, the beam splitter 18 introduces laser radiation into the measuring cell 2, which is equipped with angular reflectors 11 and 12 located on the optical axis at the input and output of the measuring cell 2. U sensible reflectors have the ability to reflect incident optical radiation back exactly in the direction of arrival of this radiation. Corner reflectors 11 and 12 form an optical resonator in which a measuring cell 2 is inserted. A probe laser pulse introduced into such a resonator will make many passes along the optical axis until it is completely absorbed in the coolant substance - in a boric acid solution. With multiple passage of a laser pulse introduced into a given optical resonator with each new passage along the optical axis of the measuring cell 2, a part of the probe laser pulse will be branched off through the beam splitter 18 back to the input of the second fiber adapter 17, and this radiation coming back to the input of the fiber adapter 17 propagates exactly in the direction of the radiation emanating from the adapter due to the properties of radiation reflection by corner reflectors 11 and 12, that is, it has the exact match of the backward propagating backward laser pulse with the parameters of the fiber adapter 17. Next, the laser radiation pulse propagating in the opposite direction (hereinafter referred to as reverse laser radiation (OLI)) passes through the fiber optic line 15 and is directed through the first fiber adapter 16 to the first translucent mirror 32. After reflection from the translucent mirror 32, the reverse laser radiation enters the fourth translucent mirror 35, through which the reverse laser The radiation is incident simultaneously at the input of the second laser modulator 9 and at the input of the fourth controlled attenuator 27. From the output of the second laser modulator 9, the reverse laser radiation is supplied to the optical input of the first photodetector unit 4, and the output from the fourth controlled attenuator 27 is fed back to the optical input of the second photodetector unit 5. Photodetector units 4 and 5 register the reverse laser radiation in the form of a series of short pulses generated at p the propagation of the initial probe laser pulse from the first laser generator 1 in the measuring cell 2 and the multiple reflection of this pulse from the beam splitter 18. In this case, the second photodetector 5 together with the fourth controlled attenuator 27 is configured for reduced sensitivity and receives and records the first time pulses of the reverse laser radiation that has traveled a short distance in the test substance of the coolant, experienced low absorption and, therefore, has a large energy level and (intensity amplitudes). The second photodetector unit 4 is configured for extremely high sensitivity and receives and registers pulses of reverse laser radiation, which have traveled a long way in the studied substance of the coolant along the measuring cell, which have experienced high absorption and, therefore, have a small amplitude level. In time, these return pulses of LI with a small amplitude are separated from the first reverse laser pulse with a large amplitude at some relatively large distance equal to the time of the multiple passage of the initial probe laser pulse along the measuring cell 2. In laser pulses that have traveled a long path through the studied coolant , it is possible to measure low concentrations of boric acid. The second laser radiation modulator 9 performs the functions of a gating stage and ensures the transmission of these low-amplitude return pulses of laser radiation to the input of a highly sensitive photodetector 4, for which, for example, a photoelectric multiplier can be used. Moreover, this laser radiation modulator 9 protects the highly sensitive photodetector unit 4 from the first reverse laser pulses having a large amplitude level. The second photodetector unit 5 is protected by a fourth controlled attenuator 27, the transmittance level of which is selected so that without overload it is possible to receive and register the first reverse laser pulses of large amplitude in the photodetector unit 5. In this case, the photodetector unit 5 loses the ability to receive and register reverse pulses with a small amplitude, which necessitates the use of a photodetector unit 4 with high sensitivity and a second laser radiation modulator 9 to protect it from the first high-energy reverse laser pulses. In FIG. 6 conventionally shows a series of pulses of reverse laser radiation recorded by the first 4 and second 5 photodetector blocks. The first most intense pulse of reverse laser radiation, indicated by pos. 51 in FIG. 6, is recorded at time t _{1 by the} second photodetector unit 5. At time t ₂ , the second laser modulator 9 is turned on (open), which remains open until a given time t ₃ or an even longer time and transmits all of the latter pulses of reverse laser radiation with small amplitudes. At 52 in FIG. 6, a gating control pulse arriving at the control input of the laser radiation modulator 9 from the processing and control unit 6 is indicated, and this modulator is opened at the time of reception and registration of pulses of reverse laser radiation with small amplitudes. The formation of the gate pulse 52 at time t _{2 is} carried out in the processing and control unit 6 with a shift relative to time t _{1 of the} appearance of the first pulse of the reverse laser radiation, which is recorded by the second photodetector unit 5 and information about which and about time t ₁ enters the processing unit and control 6. Thus, the photodetector units 4 and 5 receive and register the amplitudes of the pulses of the reverse laser radiation generated by the multiple propagation of the initial probing and pulse of laser radiation in the substance of the coolant along the optical axis of the measuring cuvette 2. The amplitudes of these laser pulses lies parameter information of coolant in a nuclear reactor circuit, namely, information on the concentration of boric acid in the coolant composition. Moreover, when measuring high concentrations of boric acid, the measurement is carried out with high accuracy on the basis of determining the amplitude of the first pulse of the reverse laser radiation in accordance with the previously presented formula (1). This measurement is carried out by means of the second photodetector unit 5. Measurement of low concentrations of boric acid is carried out on the basis of measuring the amplitudes of the pulses of reverse laser radiation, which have traveled a long way in the measuring cell 2 and recorded by the first photodetector unit 4 within the operating time of the strobe pulse 52 (t ₂ -t ₃ ) In this case, the boric acid concentration for the indicated pulses of reverse laser radiation is also determined on the basis of formula (1), and for the path length traveled by the laser pulse in the coolant substance, instead of the length of the measuring cell L, substitute the path length traveled by the laser probe pulse during repeated passage through measuring cell 2. This value of the distance traveled

Here N is the number of the detected pulse of the reverse laser radiation, counted from the first pulse of the reverse laser radiation (see pos. 1 in Fig. 6); L is the length of the measuring cell. A multiplier equal to two appears when taking into account the double passage through the measuring cell 2 of each reverse pulse, including the first pulse of the reverse laser radiation, pos. 51 in FIG. 6. Thus, the formula for determining the concentration of boric acid C in the composition of the coolant based on the amplitude I (N) of the N-th pulse of the reverse laser radiation takes the following form:

Here, the value of I should be substituted with the value of the measured pulse of the reverse laser radiation with the number N: I = I (N). The amplitude of this pulse is measured by the first photodetector 4. As follows from formula (7), the sensitivity of the measurement system increased by a factor of N, which is caused by an increase in the path length of the probe laser pulse through the substance of the coolant by a factor of N. Information on the magnitudes of the pulses of reverse laser radiation I (N) recorded by the first photodetector unit 4 and the second photodetector unit 5 is received from the outputs of these units in digital form to the individual inputs of the processing and control unit 6. In block 6, the calculation is performed according to the above formula (7 ) the concentration of boric acid in the composition of the coolant. The concentration value C is calculated separately for each detected laser pulse with number N. Moreover, to determine large levels of concentration C, it is sufficient to restrict oneself to the first laser pulses recorded in the second photodetector unit 5. When measuring low levels of concentration C of boric acid, the concentration C is determined at based on the measured values of the levels of pulses of reverse laser radiation with large numbers N - the number of revolutions of the probe laser zlucheniya the measuring cuvette 2. The accuracy of measuring the concentration of C will be greater than with a larger number N is used reverse pulse laser light I (N) to calculate the concentration of C in the above formula (7).

It should be noted that in order to separate pulses of reverse laser radiation in time for separate recording, digitization, and measurement of each pulse in photodetector blocks 4 and 5, the duration of the initial probe laser pulse coming from the output of the first laser radiation modulator 10 to the input of the measuring cell 2 should satisfy some requirements. The indicated pulse duration of the probe laser radiation should be less than twice the propagation time of light from the beam splitter 18 to the second corner reflector 12. In this case, the reverse laser pulses branched by the beam splitter 18 to the input of the second fiber adapter 17 for each revolution of the passage of the laser pulse through the measuring cell 2, are separated in time and arrive in a separate form sequentially in time to the photodetector blocks 4 and 5 for separate registration and digits. When using a measuring cell with a length L = 1 m, the duration of the probe laser pulse should not exceed seven nanoseconds. Such a pulse duration is capable of forming modern electro-optical and acousto-optical modulators of laser radiation produced by industry. There are also visible and UV laser generators that generate pulses of laser radiation with a duration of 1-3 nanoseconds. When using laser generators 1 and 7, generating laser pulses with the required short duration, the first laser radiation modulator 10 is used for a predetermined attenuation of the generated laser pulses. Thus, the measuring cuvette 2 together with the corner reflector 12 performs the additional function of an optical delay line to provide separate registration of pulses of reverse laser radiation in the photodetector blocks 4 and 5.

To determine the concentration C in accordance with formula (7), it is necessary to measure with high accuracy the level of the initial probe laser radiation I ₀ received at the optical input of the measuring cell 2 from the first beam splitter 18. Namely, the value of this level of laser radiation should be substituted into the main formula (7) . To determine this level of the initial probe laser radiation, a special calibration mode of the photodetector blocks 4, 5 and 8 of the measurement system is carried out. The level of the probe laser radiation with each emitted pulse of the laser generators 1 or 7 is measured and recorded by the third photodetector 8. For this, a fixed part of the probe laser pulse from the output of the first modulator LI 10 is branched off through the first translucent mirror 32 and fed to the input of the first through the second translucent mirror 33 controlled attenuator LI 24. From the output of the last impulse LI is fed to the input of the third photodetector unit 8, where the level is recorded and digitized of each incoming pulse DO. At the same time, as noted above, the pulse of probe laser radiation (LI) from the output of the first LI 10 modulator through sequentially optically coupled first translucent mirror 32, first and second fiber adapters, and a fiber optic line (pos. 16, 15, 17) and by the first beam splitter 18 enters the optical input level measuring cuvette 2. The magnitude of the probing laser radiation I ₀ on the optical input of the measuring cell is connected with a fixed coefficient linear pulse level LEE registered by a second photodetector unit 8. This fixed coefficient is determined by the known technical parameters of the transmission of these elements through which the pulse of the probe LI from the output of the first modulator LI 10 passes to the optical inputs of the measuring cell 2 and the third photodetector unit 8, and is also determined by the transmission of the first controlled attenuator LI 24, the transmission of which is set by commands from the processing and control unit 6. Thus, in the processing and control unit 6 based on the input from the third of the photodetector unit 8 for information about the level of the detected LI pulse, an accurate estimate of the level of the probe laser radiation I ₀ arriving at the optical input of the measuring cell 2 is formed. Further, based on this estimate and the measured levels of the inverse probe pulses I (N) of the laser radiation in the processing and control unit 6, the concentration C of boric acid is determined by the formula (7), as noted above. It should be noted that in the processing and control unit 6, when calculating the concentration C according to formula (7), additional energy losses of the probe laser pulse are propagated during its propagation through the measuring cell 2 due to the radiation branch when passing through the first beam splitter 18, and losses are also taken into account radiation when passing through fiber adapters and a fiber optic line. These losses are fixed and known from the parameters of the used optical elements. In the formula (7), for simplicity, these constant parameters are omitted.

Calibration of photodetector blocks 4, 5 and 8 is carried out in a special mode of operation of the measuring system. To implement this calibration mode, the second remote mirror 22 is put into the entered state, pos. 36 in FIG. 1. At the same time, the arrival of the LI reverse pulses from the output of the first fiber adapter 16 to the fourth translucent mirror 35 and the subsequent optical inputs of the controlled attenuator 27 and the LI modulator 9 are blocked. Instead, a probe laser pulse from the laser generator 1 or a laser generator 7 from the output of the first LI modulator 10. The pulse of the probe laser radiation arrives at the translucent mirror 35 as follows. From the output of the first laser radiation modulator 10, the probe LI pulse first arrives at the optical input of the third controlled attenuator 26 through reflection from the first translucent mirror 32 and then after reflection from the second translucent mirror 33 and reflection from the second reflective mirror 29. Next, the probe LI pulse from the output of the third controlled attenuator 26 comes after reflection from the third reflection mirror 30 and after reflection from the second extension mirror 22 at position 36 to the fourth translucent mirror 35. The latter branches the probe laser pulse into two pulses of laser radiation and directs them in parallel to the optical inputs of the fourth controlled attenuator 27 and the second laser radiation modulator 9. From the outputs of the last pulses of the probe laser radiation are fed to the optical inputs of the second 5 and first 4 photodetectors, respectively blocks where they are recorded and digitized pulse amplitude. Further, information about the amplitudes of the registered probe pulses is received from the outputs of the photodetector units 4 and 5 to the inputs of the processing and control unit 6, where it is stored in special memory registers. Moreover, as indicated above, the third photodetector unit 8 also records and digitizes the amplitude of a given laser pulse generated at that moment by the laser generator 1 and transmitted through translucent mirrors 32, 33 and through the first controlled attenuator 24. Thus, at of generating one pulse of the probe laser radiation by the laser generator 1 (or 7) and passing this pulse through the first laser radiation modulator 10, this LI pulse is simultaneously recorded in EMI three photodetector 4, 5 and 8, whereby the calibration is carried photodetecting units and linking their readings to a single scale of measurement of laser pulses amplitudes. Moreover, in the processing and control unit 6, the transmission parameters of all the above optical elements known in advance are taken into account, as well as the transmission of controlled attenuators pos. 24, 26 and 27 and taking into account the transmission of the second laser radiation modulator 9, through which the specified laser pulse passes. The transmission of the controlled attenuators and the second LI 9 modulator is controlled and set to a predetermined value according to the control commands from the processing and control unit 6. Moreover, the specified transmission values are set according to the commands from block 6 depending on and in accordance with the energy (power) of the radiation from the laser generator 1 ( or 7) and in accordance with the sensitivity of the photodetector units used. Calibration of the photodetector blocks is carried out separately for the used laser generators pos. 1 and pos. 7. The photodetector units are sensitive in both wavelength ranges generated by laser generators 1 and 7. In this case, the first laser generator 1, as was indicated, generates LI in the ultraviolet range, in which boric acid has the highest absorption. The second laser generator 7 generates in the visible wavelength range and is used to test and control the transmission of the measuring cell 2 in the operating mode. The results of the calibration are stored in the processing and control unit 6 and are used when measuring the concentration of boric acid in the measuring cell 2 and performing calculations in accordance with formula (7).

An important factor in increasing the sensitivity and accuracy of measurements is the use in the proposed measurement system of a special reference cell pos. 3. This reference cuvette is a complete analogue of the measuring cuvette 2, in particular, all the elements of the reference cuvette 3 mounted on the optical axis of the reference cuvette 3 are similar to the corresponding elements of the measuring cuvette 2 (elements 13, 19, 3, and 14). The reference cell 3 is equipped with a special unit for filling the working substance 38. Using this block 38, the reference cell 3 is filled with a boric acid solution of known concentration C, and which is carried out by the operator. Measuring cell 3 and all measuring equipment, except measuring cell 2, are located in a room separate from the reactor zone, not exposed to radiation, and are available for maintenance by operating personnel. Using the reference cuvette 3 is the automatic functional control (AFC) of the proposed measurement system. This mode of operation is necessary to improve the accuracy of the measurements, as well as to increase the reliability of the results obtained in a nuclear reactor. When a reference cuvette 3 is included in the measurement process, the first remote mirror 20 is inserted into the optical circuit using the control unit 21 and is set to the position indicated by position 37 in FIG. 1. By this action of the control unit 21, the reference cuvette 3 is turned on in the optical measuring system and the measuring cuvette 2 is turned off. The extension mirror 22 is put into the output state, as shown in FIG. 1, pos. 22. Next, the measurement of the transmission parameters of the substance in the reference cuvette 3 is carried out, similarly to how it is carried out for measurements in the reference cuvette 2 in accordance with the procedure described above. The pulse of the probe laser radiation from the output of the first modulator of laser radiation 10 through the first translucent mirror 32 and after reflection from the first remote mirror 20 at position 37 is fed to the optical input of the second controlled attenuator 25. From the output of the last probe pulse after reflection from the fourth reflective mirror 31 enters the second beam splitter 19, which is used as a translucent mirror. Using a beam splitter 19, a probe laser pulse is introduced into a reference cell 3, similar to how it was introduced when a probe laser pulse was introduced into a measuring cell 2. The difference is the absence of a fiber optic line with fiber adapters. The optical transmittance of these elements in the reference cuvette 3 is modeled and provided using the second controlled attenuator 25. The transmission of the controlled attenuator 25 is set equal to the transmittance of the fiber optic line 15 with fiber adapters based on the passport data for these elements, as well as by equalizing the transmittance during operation of the second laser generator 7. Thus, the pulse of the probe laser radiation is introduced into the reference cell 3 and then propagates in it in the forward and reverse directions until complete absorption. The pulses of the reverse laser radiation after the second beam splitter 19 are branched back to the fourth reflective mirror 31 and then through the second controlled attenuator 25, and also after reflection from the first remote mirror 20 at position 37 and after reflection from the first translucent mirror 32, they are transmitted to the fourth translucent mirror 35. In this case, the second remote mirror 22 is withdrawn from the optical circuit and is in position 22, as shown in FIG. 1. The fourth translucent mirror 35 directs the pulses of the reverse laser radiation to the optical inputs of the fourth controlled attenuator 27 and the second laser radiation modulator 9. Next, the pulses of the reverse laser radiation arrive from the outputs of the last elements to the optical inputs of the first and second 4 and 5 photodetector blocks, where they are reception and registration. In digital form, pulses of reverse laser radiation are fed to the inputs of the processing and control unit 6 for storing and subsequent processing. Thus, in the process of measuring the parameters of the pulses of the reverse laser radiation for the reference cell 3, the same procedure is carried out as when performing measurements with the measuring cell 2. The reception and registration of pulses of the reverse laser radiation that arise (excited) from the passage through the reference cell 3 of one source the probe laser pulse is carried out separately when the first laser generator 1 is operating at a certain wavelength in the ultraviolet range, and then when the second laser is operating of the generator 7 to a second wavelength in the visible range in which the absorption of radiation of boric acid is almost zero regardless of the concentration of boric acid. In this second case, with the optical identity of the measuring and reference cuvettes, the levels of the recorded pulses of the reverse laser radiation at the wavelength of the second laser generator 7 should be the same for the measuring 2 and reference 3 cuvettes. The values of the indicated pulses of the reverse LI are equalized during the operation of the second laser generator 7 by means of a second controlled attenuator 25, the transmission of which is controlled by commands from the processing and control unit 6, in which the indicated registered pulses of the reverse LI are compared and control signals are generated for the second controlled attenuator 25. At the same time, the first remote mirror 20 is switched quickly for periodic connection to the meter second optical circuit measuring cuvette (position of the first remote mirror at position 20) and the reference cuvette (position of the first remote mirror at position 37, FIG. 1). After equalizing the optical values of the reverse LI pulses for the measuring 2 and reference 3 cuvettes, the actual mode of measuring the concentration of boric acid in the coolant circuit is carried out using the measuring cuvette 2 as described above. In this case, various algorithms for determining the concentration of boric acid are possible. The simplest method is the method described above for determining the concentration C using formula (7) based on the recorded levels I (N) of the pulses of the reverse laser radiation and estimating the level of the initial probe radiation I ₀ at the entrance to the measuring cell 2, which was obtained by calibrating the photodetector blocks and based on the level of the laser pulse recorded by the third photodetector 8. The magnitude of the extinction coefficient K of boric acid for the used wavelength of the first laser generator 1 is determined from reference data, or can be measured experimentally in the proposed measuring system using a reference cell 3, if it is filled with a boric acid solution with a known predetermined concentration C. When continuously monitoring the parameters of the coolant in the nuclear reactor loop, the concentration of boric acid is measured repeatedly with interruptions in the form of certain intervals of time. In this case, the state of the measuring cell 2 is monitored in the time intervals between the actual measurement of the concentration of boric acid C in the measuring cell 2. To perform this control, the first laser generator 1 is turned off and the second laser generator 7 is turned on, operating on a longer wavelength of laser radiation in the visible range , on which the optical parameters of the measuring cell and the reference cell are the same, as noted above. Next, registration is performed using the first 4 and second 5 photodetector blocks of pulses of reverse laser radiation when illuminated by a probe pulse LI from the second laser generator 7 as measuring 2 and reference 3 cuvettes. Comparison of the indicated recorded pulses of the reverse LI allows us to judge the normal standard state of the measuring cell 2, which is in a room inaccessible to the operating personnel near the existing nuclear reactor. This allows you to increase the reliability and confidence of the received information about the parameters of the coolant during continuous long-term operation of a nuclear reactor.

The first 4 and second 5 photodetector units together measure the concentration of boric acid in a wide range of concentration C. The second photodetector unit 5 measures large levels of concentration C when registering reverse LI pulses that have passed one (N = 1) or several revolutions during propagation along the measurement cell 2. In this case, the determination of the concentration level C is carried out according to the formula (7). To improve the accuracy of measuring large levels of concentration C, it is possible to use the comparison of the obtained amplitudes of the pulses of the reverse LI passed through the measuring cell 2 with the amplitudes of the pulses of the reverse LI passed through the reference cuvette 3 when filling this cuvette using the filling unit 38 with boric acid solution with concentration C, obtained in the previous measurement in the measuring cell 2. Such a measurement method when performing direct comparison of measurements in both cuvettes for the obtained parameters Center C will improve the accuracy and reliability of the measurements. This comparison method is also possible when measuring low concentrations of C based on the values of the pulses of the inverse LI recorded in the first photodetector unit 4.

The most accurate method for measuring low concentrations of boric acid is the method of directly comparing the values of the pulses of the reverse LI recorded in the first photodetector 4 when the probe radiation of the measuring cell 2 is illuminated by a probe pulse with the values of the pulses of the reverse laser radiation obtained by the transmission of the reference cell 3, provided filling this cuvette with distilled water, that is, at zero concentration C = 0 of boric acid in the reference cuvette 3. At the same time, s is performed for the amplitudes of pulses of the inverse of the laser radiation with the same number of revolutions N of passage of the probe pulse laser beam 2 on the measuring and reference 3 cuvette. Measuring 2 and reference 3 cuvettes are illuminated by laser pulses generated by the first laser generator 1 in the ultraviolet wavelength range at a certain fixed radiation wavelength. In this case, the switching of the measuring and reference cuvette to the input of the optical measuring circuit is carried out using the first remote mirror 20, as noted earlier. The photodetector unit 8 performs registration of the level of the emitted probe pulse of the laser radiation for each individual act of measuring the amplitudes of the pulses of the reverse laser radiation. In the processing and control unit 6, a series of pulse amplitudes of the reverse laser pulses I ₀ (N) and I (N) measured by the photodetector blocks 4 and 5 is recorded. Here, I ₀ (N) are the amplitudes of the pulses of the reverse LI obtained by transmission of the reference cell 3 with zero concentration of boric acid by probing laser radiation with C = 0; the values of I (N) are the amplitudes of the pulses of the reverse laser radiation obtained by transmission of the measuring cell 2 with the desired value of the boric acid concentration C; N is the number of revolutions of the probe pulse along the measuring or reference cuvettes, the same for the compared pulses of the reverse PI. The measurement is carried out at the same wavelength of the probe laser radiation generated by the first laser generator 1. The ratio of the values of the indicated pulses of the reverse laser radiation can be represented in the following form:

Thus, with respect to the amplitudes of the indicated reverse laser pulses for the measuring and reference cuvettes, all transmission parameters of the elements of the optical scheme and the levels of the probe laser radiation are excluded, except for the parameters of the desired concentration of boric acid C in the coolant of the nuclear reactor and the extinction values of K boric acid for the used length laser radiation waves, the length of the measuring (and reference) cuvette L and the number of revolutions N of the probe laser radiation along the measuring cuvette.

The obtained ratio of values (8) allows us to calculate the concentration of boric acid in the following form:

Formula (9) determines the desired concentration of boric acid C in the form of the ratio of the known values of K, L, N and the measured physical quantities - the indicated amplitudes of the pulses of the reverse laser radiation. The accuracy of the measurements of these laser pulses can be quite high when using modern highly sensitive UV-photodetectors and relatively powerful UV-wavelength laser generators. The adjustment of the parameters of the measuring and reference cuvettes and the compensation and elimination of the influence of transmission of the elements of the optical circuit when connecting the measuring and reference cuvettes allows to increase the accuracy of measurements of small concentrations of boric acid in the composition of the coolant in the measuring cell 2.

As can be seen from (9), the possibilities of measuring low concentrations of boric acid C are determined by the level of attenuation (decrease) of the pulse of the reverse laser radiation I (N) upon repeated passage through the measuring cell. This attenuation, as was shown above, is proportional to the value of exp (KCLN), which increases with increasing number of revolutions N of the probe laser pulse. This proves an increase in the possibility of measuring low concentrations and an increase in the accuracy of measurements when using the proposed measurement method with the multiple passage of the probe laser radiation through the measuring cell.

The calculation of the measured concentration value of boric acid concentration C according to the presented formula (9) is carried out promptly in the processing and control unit 6 based on the measured values of the amplitudes of the pulses of the reverse laser radiation. Then the received information is sent to the central control panel of the nuclear power plant. This completes the cycle of measuring the concentration of boric acid in the coolant of a nuclear reactor.

Based on the materials of this application, an experimental (experimental) sample of a boric acid measurement system was developed and studied, various concentrations of boric acid solutions were measured and boric acid extinction coefficient was measured for various probing radiation wavelengths, and the operation of a boric acid measurement system in the coolant circuit was simulated, the results of which are given below. The extinction coefficient K was measured on a reference cuvette when it was filled with a boric acid solution of a previously known (prepared) concentration of C _et . Next, the optical parameters of the input and transmitted optical radiation were measured. The determination of the extinction coefficient K was carried out in accordance with the basic equation (1), which was solved with respect to an unknown value of K for other known and measured values. As a result, the magnitude of the extinction coefficient K was determined from the following ratio:

The following are the results of measuring the concentration of boric acid carried out using the proposed measuring system using UV radiation with a wavelength of about 220 nm and for the extinction coefficient K corresponding to this wavelength and equal to K = 1.64 × 10 ^-4 l⋅cm ^{- 1} г mg ^-1 . The measurements were carried out in accordance with relation (8) for the following parameters of the optical scheme: the length of the measuring (and reference) cell L = 100 cm. The number of passes N varied from 1 to 30 passes of the probe laser radiation through the measuring cell.

For modeling, three concentrations of boric acid were chosen: C = 1 mg / L, 0.2 mg / L and 0.05 mg / L. The results obtained showed the ability to measure these low concentrations of boric acid using the proposed measurement system. Further, the obtained simulation results of the parameters of the measuring system are presented for each value of the concentration of boric acid With as follows.

The dependence of the ratio E _{p of the} amplitude I (N) of the Nth pulse of the reverse laser radiation that has passed N revolutions through the measuring cuvette 2 to the amplitude I ₀ (N) of the same Nth pulse of the reverse laser radiation that has passed N revolutions but according to the reference cuvette 3, in which the concentration of boric acid is zero and which is filled with distilled water:

This ratio E _p is, as follows from formula (9), the main value by which the concentration of boric acid C is determined. The simulation results are presented in table. one.

According to the measurement results presented in Table 1, it is seen how, with an increase in the number of revolutions N of the probe laser pulse, the sensitivity of the measurement system increases along the measuring cell and it becomes possible to measure lower concentrations of boric acid in the composition of the coolant of a nuclear reactor. So, for example, when measuring the concentration of boric acid C = 1 milligram per liter of coolant substance, it is quite enough to use ten revolutions of the probe LI pulse along the measuring cell. With this number of revolutions N = 10, the value of the attenuation of the reverse pulse is E _p = 0.848 compared to the pulse transmitted through a reference cell with a zero concentration of boric acid. That is, the attenuation of the LI pulse passing through the coolant layer, in comparison with the reference pulse, is 15.2 percent, which is quite sufficient for high-precision measurements. Accordingly, the attenuation of the LI pulse passing through the measuring cell at a concentration of C = 0.2 mg / L is about 10% when using N = 30 revolutions of passage through the measuring cell, which also ensures high measurement accuracy. The limiting minimum value of the measured concentration of boric acid at these selected parameters of the measuring system is C = 0.05 mg / l of the coolant substance (50 μg / l) and is achieved at a speed of N = 30. The limiting (threshold) sensitivity of the proposed measuring system, calculated by the formula (5), at N = 30 revolutions is C = 0.02 mg / l of the coolant substance. This value also characterizes the accuracy of measurements of the concentration of boric acid in the composition of the coolant of a nuclear reactor. It should be noted that the implementation of measurements at a large number of N revolutions (passes) of the probe laser pulse along the measuring and reference cuvettes is ensured by a sufficiently high energy level of the generated laser radiation and high sensitivity of the photodetector units 4 and 5. This is achieved through the use of modern laser generators and highly sensitive ultraviolet wavelength photodetectors. The implementation of a large number of passes (revolutions) of the probe laser radiation through the measuring cuvette is ensured by a significant reduction in radiation losses per cycle through the measuring cuvette 2, which is achieved through the use of corner reflectors that provide optical feedback for repeated passage of the laser radiation through the cuvette 2. feedback loop eliminates the fiber optic line and additional connecting optical elements, which reduces radiation loss at each revolution L And on the measuring cell 2 and allows you to increase the total number of passes N of the probe LI through the cell with the used laser generators 1 and 7, with a limited generated radiation power. The use of a large number of revolutions N of the probe laser radiation using a measuring cuvette 2, in turn, makes it possible to increase the sensitivity of the used absorption photometric measurement method, which ensures high accuracy when measuring very low concentrations of boric acid C in the composition of the coolant of a nuclear reactor.

Table 2 presents the results of measurements of relatively high concentrations of boric acid from 10 to 100 mg / l of coolant obtained for a single passage of a probe laser pulse through a measuring cell at N = 1.

As can be seen from table 2, when measuring high levels of boric acid concentration, to ensure high measurement accuracy, a single passage of the probe pulse through measurement cuvette 2 is sufficient. Moreover, the attenuation level of the reverse LI pulse compared to the reference pulse of the reverse LI varies from 15% at C = 10 mg / l to 81% at C = 100 mg / l.

In FIG. 7 presents the results of modeling the operation of the measurement system in accordance with table. 1 when carrying out measurements of the concentration of boric acid C = 1 mg / l of a coolant substance. In FIG. 7 shows a sequence of pulses of reverse laser radiation I (N) / I ₀ (N) with respect to the values of pulses of reverse laser radiation I ₀ (N) transmitted through a reference cell 3 with a zero concentration of boric acid C = 0. These reverse LI pulses are recorded by the photodetector unit 4 after each passage of the probe pulse through the measuring cell 2 and the pulses I ₀ (N) are separately recorded after passing through the reference cell 3. Moreover, the relative magnitude of the reverse LI pulses I (N) / I ₀ (N) gradually decreases with increasing number of revolutions N in the measuring cell 2. The number of revolutions (passes) in the measuring cell increases from one to N. When the number of revolutions N = 10, the value of the recorded pulse I (10) is 0.848 of the value of the pulse I ₀ (0), reg abraded at zero concentration of boric acid (in the reference cuvette) - a change of 15.2%. Thus, even at N = 10 revolutions of the probe pulse, accurate measurements of the concentration of boric acid of the order of C = 1 mg / L are possible. At N = 20, the indicated change (decrease) in the pulse amplitude is 0.72 of the pulse level at zero concentration of boric acid (decrease by 28%), which allows the measurement process to be performed with even higher accuracy. With a single passage of the probe pulse I (1) through the measuring cell, the decrease in amplitude relative to the zero pulse I ₀ (0) will be 0.9837, i.e. less than one percent, which does not allow to ensure high measurement accuracy with only one passage of the probe pulse through the measuring cell, which is typical for the classical absorption method. Thus, shown in FIG. 7, the result shows a gradual increase in the sensitivity and accuracy of measurements with an increase in the number of passes N of the probing laser radiation along the measuring cell 2. Presented in FIG. 8 and FIG. 9, the results of modeling measurements of boric acid concentrations of 0.2 mg / L and 0.05 mg / L showed a definite possibility of fairly accurate determination of these low levels of concentrations. For example, when measuring a very low concentration C = 0.05 mg / L, the level of decrease in the amplitude of the probe pulse I (N), which must be recorded at N = 30 after thirty revolutions of the probe pulse through the measuring cell, is E _p = 0.975, t .e. 2.5%. Modern digital means of measuring the amplitudes of electric pulses reliably provide this measurement accuracy, which accordingly provides sufficient accuracy for measuring a very low concentration of boric acid in the composition of the coolant circuit of a nuclear reactor.

It should be noted that when switching from measurements of a low concentration of boric acid to measurements of a higher concentration, it is advisable to change the working wavelength generated by the first laser generator 1 and use longer wavelength ultraviolet laser radiation. This will allow you to more accurately match the characteristics of the photodetector blocks 4 and 5 with the characteristics of the absorption of radiation in a coolant with a higher concentration of boric acid and will provide higher measurement accuracy. Currently, the industry has mastered the laser generators of the visible and ultraviolet wavelength range with the tuning of the wavelength of the generated radiation. Similarly, when using the second laser generator 7 with tuning the wavelength of the generated radiation, a more accurate joint calibration of the measuring and reference cell at several wavelengths of the control radiation is possible.

The proposed measurement system uses blocks and units developed or manufactured by the industry. The measuring and reference cuvettes are made in the form of standard design developments using portholes that are transparent in a wide range from a short part of the UV range to the IR wavelength range. UV laser generators and photodetectors are manufactured by industry and are used in industry, medicine, and research. The optical instruments and elements that make up the proposed measuring system are designed and manufactured by the industry. Such elements include optical reflective and translucent mirrors, remote mirrors with a drive based on stepper motors, fiber optic lines with fiber adapters included in their composition for a range from 200 nm to the IR range, laser radiation modulators based on acousto-optical cells and based electro-optical crystals operating in a wide range of wavelengths from visible to ultraviolet. Controlled attenuators are made on the basis of, for example, diaphragms mechanically controlled by stepper electric motors, or based on electro-optical crystals. The control units of controlled attenuators and modulators of laser radiation are included in their composition and are not shown in FIG. 1. The photodetector blocks 4, 5 and 8 are made on the basis of a highly sensitive photoelectronic multiplier operating in the range of 200-800 nm. The composition of the photodetector blocks includes electrical amplifiers of pulsed signals, blocks of digitization and interface with the input of the computer. The processing and control unit 6 is made on the basis of a standard electronic computer of any type. Block 6 performs the functions of processing the information coming from the outputs of the photodetector blocks, on the basis of which the calculation and determination of the concentration of boric acid in the coolant circuit of a nuclear reactor are carried out. At the same time, block 6 controls the operation of all elements and devices of the measurement system according to a special program. Block 6 contains means for interfacing and is connected to all controllable elements of the measuring system.

In the proposed measurement system, various options for constructing the main optical functional units are possible. In FIG. Figure 2 shows the second option for connecting the fiber optic line and the second fiber adapter to the input of the measuring cell 2. This option for delivering a probe laser pulse to the optical input of the measuring cell 2 is characterized in that the first corner reflector 11 and the second fiber adapter 17 are swapped compared to FIG. 1. In FIG. 3 shows a third embodiment of connecting a second fiber adapter 17 to the optical input of the measuring cell 2. FIG. 3, the role of the corner reflector 11 is played by the first beam splitter 18, which is made on the basis of a translucent mirror. At the same time, this beam-splitting translucent mirror 18 is installed perpendicular to the optical axis of the measuring cell 2 and performs two functions: the reflective mirror itself, which replaces the corner reflector, and the beam-splitting function when a probe laser pulse is transmitted to the optical input of the measuring cell from the optical output of the second fiber adapter 17. In this case, the corner reflector pos. 11 is excluded from the optical system of the measurement system. Physically, these options for constructing the delivery of laser radiation to the input of the measuring cell 2 in FIG. 2 and FIG. 3 are equivalent to the embodiment shown in the main figure, FIG. one.

In FIG. 4 shows a design option for the delivery of a probe laser pulse to the optical input of the measuring cell 2, in which pos. 18 (in Fig. 1) used acousto-optic cell pos. 39 with a control unit 40. This acousto-optical cell 39 plays the role of a dynamic optical beam splitter - a switch of optical pulsed radiation and provides the prompt switching of the optical input of the measuring cell 2 to the optical output of the fiber adapter 17 or switching the specified input of the measuring cell 2 to the first corner reflector 11, and reverse switching under control of signals from its control unit 40, which in turn generates control signals for the acousto-optical cell 39 under the influence of control and synchronization signals arriving at block 40 from the output of the processing and control unit 6. At the first instant of time, the probe pulse LI from the output of the fiber adapter 17 to the optical input of the measuring cell 2, the acousto-optical cell 39 works as a plane-parallel plate, through which laser radiation from the output of the fiber adapter 17 passes without loss to the optical input of the measuring cell 2. At this point in time, a control signal from the output of the control unit is transmitted to the acousto-optical cell 39 Lenia 40 is not served. Next, the pulse of the probe LI passes through the AO cell 39 and fills the measuring cell 2. After that, a control electric signal is supplied to the acousto-optical cell 39 from block 40, under the influence of which this AO cell switches the optical input of the measuring cell 2 to the corner reflector 11. In this case, multiple the passage of the probe laser pulse along the measuring cell 2 in the forward and reverse directions, which is ensured by the reflection of the specified pulse from the corner reflectors 11 and 12. C It should be noted that when an acousto-optic cell operates in the mode of switching the light flux to the corner reflector, the Bragg diffraction mode is used in which more than 95% of the switched light flux is directed to the corner reflector, and radiation losses are minimal. Some time after the LI pulse performs a certain specified number of revolutions N in the measuring cell 2, the control electric signal from the output of block 40 from the acousto-optic cell 39 is turned off, and the latter again operates as a plane-parallel plate transmitting laser radiation from the output of the measuring cell to the fiber adapter 17, then there is switching the measuring cuvette 2 again to the input of the fiber adapter 17. The pulse of the reverse laser radiation from the output of the measuring cuvette 2 after making N turns goes to the input of the fiber adapter 17 and then through the optical fiber line 15 passes through the corresponding optical elements to the optical inputs of the first and second photodetector units 4 and 5. This option for constructing a pulse delivery probe probe line has less energy loss from the probe pulse due to direct operational switching of the optical the input of the measuring cell 2 to the output of the fiber adapter and to the corner reflector, in which energy losses in the passive beam splitter 18 are excluded, when used in this oli standard semitransparent mirror, having a fixed predetermined level and the transmission simultaneously toward corner reflector 11 and the side fiber adapter 17, which occur when certain fixed losses in the energy delivered to the laser probe and reverse filmed laser pulses. However, the use of modern high-power laser generators and highly sensitive photodetectors makes these losses insignificant and allows using a simpler scheme for delivering probe laser radiation to the input of the measuring cell 2 based on a simple translucent mirror as a beam splitter 18, as shown in FIG. 1. For example, when using a translucent mirror 18 as a beam splitter, having a transmittance in the direction along the optical axis of the measuring cell equal to 0.9 and, accordingly, a transmittance in the lateral direction of about 0.085, the possible number of revolutions of the probe laser radiation is of the order of N = 33-35 when using modern UV pulsed pulsed lasers and highly sensitive PMTs of the UV wavelength range produced by industry. The specified number of revolutions of the probe pulse LI on the measuring cell is sufficient to ensure the sensitivity and accuracy of measuring the concentration of boric acid C _min = 0.05 mg / L. The principle of acousto-optic cells and their main parameters are given in the corresponding monographs and works [8-10]. Similarly, the second beam splitter 19 can be made on the basis of an acousto-optic cell, which quickly switches the optical input of the reference cell 3 to the input of the corner reflector 13 or the fourth reflective mirror 31, which will allow for a dynamic switching mode similar to that used for the measuring cell 2.

An important problem when using the proposed boric acid measurement system in a nuclear reactor equipment is the task of connecting a measuring cell to the coolant circuit of a nuclear reactor. This problem is solved by using a special bypass pipeline - a branch from the coolant circuit of a nuclear reactor, to which a measuring cell is connected. The implementation of this connection requires significant costs during installation and commissioning of the proposed measuring system. It is possible to use the proposed measurement system as part of a nuclear reactor, which does not require a special bypass line to include the measurement system in the coolant circuit. A variant of this use of the proposed measuring system is shown in FIG. 5. In this embodiment, to fill the measuring cell 2 with the coolant of the nuclear reactor circuit, a sampling device from the nuclear reactor coolant circuit is used, which is currently available in WWER reactors and is used to measure the concentration of boric acid by the chemoluminescent method. In FIG. 5 shows conventionally the pipeline of the primary coolant circuit, pos. 42, to which through a controlled valve 44 is connected a device for sampling 43 from the coolant circuit. This device 42 is a special throttle unit to reduce the pressure of the working fluid of the coolant to normal atmospheric pressure and to cool the sample substance. Currently, from the output of the sampling device 43, the coolant substance through a controlled valve 45 enters the transfer container of the selected sample (not shown). It is proposed that the output of the sampling device 43 be connected through an additional controlled valve 46 to the measuring cell 2, which will be placed next to the sampling device 43. With the valve 46 open, the measuring cell 2 is filled with material from the coolant circuit from the output of the sampling device 43. After implementation the process of measuring the concentration of boric acid in a substance from the coolant circuit located in the cuvette 2, using a drain valve 47, the substance is drained from the measuring 2 cell into a container 48 for collecting the spent sample substance. The actual process of measuring the concentration of boric acid in the composition of the measuring cell 2 is not more than one second. Thus, this use of the proposed measurement system provides all the advantages of the above method for determining the concentration of boric acid in the composition of the coolant circuit of a nuclear reactor, but does not require the installation of a separate separate bypass for connecting the measuring cell to the coolant circuit by using the existing means of sampling the coolant. Therefore, this option does not require large capital expenditures for the implementation of the proposed measuring system in the equipment of an existing nuclear reactor. The installation of the measuring cell 2 and its connection to the sampling device 43 can be carried out in the operating mode of a nuclear reactor without stopping it. At the same time, the proposed measuring system has all the advantages over the chemoluminescent sampling method, namely: it provides higher measurement accuracy, high measurement efficiency, the possibility of repeated measurements and comparison with measurements in the reference cell, provides full automation of measurements, and also completely eliminates the contact of nuclear power plant personnel with coolant or measuring equipment.

Based on the materials of this application for the invention, a prototype of a measurement system was developed and investigated, measurements of the parameters of the studied materials and solutions of substances in distilled water were carried out, parameters of a boric acid solution of a given concentration were determined, and extinction coefficients of boric acid were measured for various wavelengths of the ultraviolet wavelength range, as well as parameters of boric acid in the blue-green region of the visible spectrum. The results obtained indicate the possibility and prospects of measuring the concentration of boric acid by the proposed method using the presented measurement system in the ultraviolet wavelength range and using the blue-green part of the visible range as control laser radiation. The proposed measurement system provides the measurement of large concentrations of boric acid of the order of tens of grams per liter of coolant. At the same time, the proposed measurement system provides measurements of small concentrations of boric acid up to values of 0.05-0.1 mg / l of coolant substance. This high sensitivity when measuring low concentrations of the investigated substances is achieved through the multiple passage of the probe laser radiation through the measuring cell using special corner reflectors. As a result of this, the sensitivity of the absorption-spectral measurement method used increases by a factor of N, where N is the number of passes (revolutions) of the probe laser radiation through the measuring cell. In addition, an increase in the sensitivity and reliability of measurements is ensured by the use of a reference cell, in which any precisely defined concentration of boric acid solution in distilled water is established. In this case, the reference cell has optical parameters identical to the measuring cell. In the measuring system, a periodic connection to the measurement scheme of the reference or measuring cell is provided. Next, a comparison is made of the parameters of the pulses of the probe laser radiation transmitted through the measuring and reference cuvettes during the same number of revolutions N through the material of the measuring cuvette or reference cuvette, which can significantly increase the accuracy and reliability of measurements and provide continuous monitoring of the coolant parameters in the primary circuit of a nuclear reactor. An important advantage of the proposed measurement system is the ability to connect to the measuring circuit and take measurements on several measuring cuvettes connected in various places of the primary coolant of the nuclear reactor. This allows you to quickly monitor the parameters of the coolant at various points in the circuit, which is important for effective and safe control of the operation of a nuclear reactor. The proposed measurement system has high speed and efficiency in carrying out measurements. Actually, the time of measuring the concentration of boric acid in the coolant passing through the measuring cell is several milliseconds and is determined by the processing time of the information in the control unit 6 (in a personal computer) obtained by registering one probe laser pulse. An important factor in increasing the accuracy of measurements, the reliability and confidence of the information received is the ability to fill the reference cell with a solution of boric acid of any given concentration, performed by the operator, subsequent measurements using this reference cell and measuring cell, processing and comparing the results. It should be noted that it is possible to check (test) the optical parameters of the measuring cell using a second laser generator and compare these parameters with the parameters of the reference cell without disconnecting the measuring cell from the primary coolant circuit in the operating mode of a nuclear reactor.

In the presented claims, in the restrictive part of the formula are the first laser generator and two photodetector units. This is due to the fact that the device adopted for the prototype [6] contains a radiation source and two photodetectors. A laser generator is generally a radiation source, and photodetector units contain photodetectors and are similar objects.

The presented system for measuring the parameters of the coolant in the circuit of a nuclear reactor is a remote-sensing measuring system that uses probing radiation transmitted through a fiber-optic line to receive information - the so-called radar tester. In this measuring system, a number of technical problems have been solved that arise similar to the problems of modern laser location [19], which can also be solved using the capabilities and achievements of modern laser technology. It can be argued that further improvement of the presented measuring system based on the use of modern and promising laser equipment being developed will allow further improvement of the characteristics of special measuring equipment for use in nuclear energy.

In the submitted application for the invention, two factors of novelty should be noted. Firstly, it should be noted as a novelty of the invention the implementation in the measuring system of a new embodiment of the absorption-spectral method of measurements based on the multiple passage of the probe laser radiation through the measuring cell, implemented by introducing an optical feedback ring directly through the measuring cell using angle reflectors, forming open optical resonator, which includes a measuring cell with a coolant substance. Similarly, optical feedback was performed for a reference cell, which is filled with a boric acid solution with a given concentration and precisely known optical parameters. This new measurement method allows increasing the sensitivity of the classical absorption-spectral measurement method by a factor equal to the number N of revolutions of the probe laser radiation along the optical feedback ring inside the measuring cell, which is especially important when measuring low concentrations of boric acid or other substances with a low coefficient extinction.

Secondly, it should be noted as a novelty of the invention the implementation of measuring the concentration of boric acid directly in the primary circuit of the coolant of a nuclear power reactor by the indicated new version of the absorption spectral optical method, ensuring high accuracy, reliability and efficiency of measurements while solving a number of problems that arise when applying modern technical means in nuclear power. It should be noted that the use of the proposed measurement system as part of a nuclear power reactor allows you to realize the following advantages and provide a solution to the following problems in the operation of modern nuclear reactors:

1) Ensuring the possibility of monitoring the composition of the coolant directly in the circuit under the current parameters of the aquatic environment. In this case, it is possible to determine the concentration of not only boric acid, but also other possible impurities formed during prolonged operation of a nuclear reactor and exposure to radiation. To detect these impurities, it is possible to use the entire spectrum of laser radiation from short ultraviolet to infrared radiation that can propagate in an aqueous medium.

2) In unattended and semi-serviced rooms of the first circuit (strict mode zone), only measuring cuvettes are installed. Ancillary equipment of the measuring system and information display devices can be taken to any room of a nuclear power plant at a distance of about 1000 meters from a nuclear reactor through the use of a fiber-optic communication line. Such a structure, with a high service life of the measuring cuvettes, will reduce the dose loads of the NPP staff.

3) The application of the proposed measurement system eliminates the need for sampling the coolant from the primary circuit. This ensures a reduction in dose loads of NPP personnel and eliminates the discharge of radioactive media obtained during sampling from the primary circuit. Thus, the operating mode of the corresponding special NPP units is softened.

4) Removing a person from the measurement process (which is typical for chemoluminescent measurement methods with sampling) eliminates the subjective random measurement error. The metrological characteristics of measurements are significantly improved due to the absence of transport delay of the sample in long pulse lines, the measurement efficiency is increased, which is of great importance for the control system of a nuclear reactor and increase the safety of nuclear power plants.

Due to the high accuracy of measurements, a wide range of measurements of the concentrations of the investigated substances and the high efficiency of measurements, the proposed measuring system will find application in various fields of production, the chemical, oil refining industry and environmental monitoring and environmental control systems.

Information sources

1. Sarylov V.I. The use of the chemoluminescent method for monitoring the parameters of the reactor water of nuclear power plants. Chemistry and water technology, 1982, T. 4, No. 1, P. 45-47.

2. Bovin V.P. Neutron-absorption analyzer of Boron in the primary coolant of the WWER. Atomic Energy, 1976.V. 38, Vol. 5, S. 283-286.

3. RF patent No. 2025800 dated 12/30/1994. The method of controlling the content of Boron-10 in the coolant of the primary circuit of a nuclear reactor.

4. England patent No. 1157086. Two-beam photometer.

5. RF patent No. 2022239 from 10.30.1994. Device for optical absorption analysis.

6. RF patent No. 750287 of 07.23.1980. Device for optical absorption analysis. Double beam photometer (prototype).

7. RF patent No. 2175792 dated 02.20.2001. Measuring device for determining the concentration of boron.

8. Balakshiy V.I., Parygin V.N., Chirkov L.E. Physical foundations of acousto-optics. M .: Radio and communications, 1985.S. 134-234.

9. Balakshiy V.I., Mankevich S.K., Parygin V.N. Quantum Electronics. 1985.V. 12, No. 4.

10. Mustel E.R., Parygin V.N. Methods of modulation and scanning of light. M .: Nauka, 1970.

11. Handbook of laser technology. // Edited by Napartovich A.P. M .: Energoatomizdat, 1991.

12. Physico-chemical methods for the study of internal contour chemical processes in atomic energy systems. Tsniato-minform, 1986.

13. Eristova D.I., Brouchek F.I. Analytical methods for determining boron. Tbilisi, 1965.

14. Marchenko Z.I. Photometric determination of elements. M.: Mir, 1976.

15. Nemodruk A.A., Karamova Z.K. Analytical chemistry of boron. M .: Nauka, 1964.

16. Chemical control at thermal and nuclear plants. M .: Nauka, 1980.

17. Lazarev N.V., Astrakhantsev P.I. Chemically harmful substances in industry, reference book. Part 2. Onti-chemtheoret, Leningrad, 1934.

18. Mankevich S.K., Nosach O.Yu., Orlov E.P. and other RF Patent No. 2248555 of 03.20.2005. A method for determining the characteristics of a laser medium and a device for its implementation.

19. Mankevich S.K., Nosach O.Yu., Orlov E.P. and other RF Patent No. 2152056 dated 06/27/2000. The method of laser location and device for its implementation.

20. RF patent No. 2179756 of 02.20.2002. Method and device for producing a liquid sample.

Claims (7)

1. A system for measuring the concentration of boric acid in the coolant circuit of a nuclear power reactor, comprising a first laser generator, a measuring and reference cell, electrically coupled a first photodetector unit and a processing and control unit, a second photodetector unit, the output of which is connected to the processing and control unit, a control input the first laser generator is connected to the processing and control unit, characterized in that a second laser generator, a third photodetector unit, a first and second modulator are introduced laser radiation, four controlled attenuators, two remote mirrors with control units, sequentially mounted on the optical axis of the measuring cell, optically coupled to the first corner reflector, the first beam splitter, the optical output of which is connected to the optical input of the measuring cell, and the second corner reflector, optically connected to the optical output of the measuring cell cuvettes, sequentially mounted on the optical axis of the reference cuvette, optically coupled to a third corner reflector, second beamsplitter a body, the optical output of which is connected to the optical input of the reference cell, a fourth corner reflector, optically coupled to the optical output of the reference cell, optically coupled to the first fiber adapter, a fiber optic line and a second fiber adapter, the optical output of which is connected to the optical input of the first beam splitter, and four reflective mirrors and four translucent mirrors were also introduced, with the output of the first laser generator through the first reflective mirror being connected to the optical input of of the second laser modulator, the output of the second laser generator through the third translucent mirror is connected to the optical input of the first laser modulator, the optical output of which through the first translucent mirror is connected to the optical input of the first fiber adapter when the first remote mirror is pulled out, the optical output of the first laser modulator when introduced the first remote mirror is optically connected to the optical input of the second controlled attenuator, the output of which is through four a worn reflective mirror is connected to the optical input of the second beam splitter, the optical input of the first fiber adapter when the first and second remote mirrors are pulled out is optically coupled through the first translucent mirror and through the fourth translucent mirror to the optical input of the second laser modulator and to the optical input of the fourth controlled attenuator, optical output which is connected with the optical input of the second photodetector unit, the optical output of the second optical laser modulator connected with the optical input of the first photodetector, the optical output of the first laser modulator through the first translucent mirror and through the second translucent mirror is optically connected to the optical input of the first controlled attenuator, the output of which is connected to the optical input of the third photodetector, the optical output of the first laser modulator the first and second translucent mirrors and the second reflective mirror is connected to the optical input of the third controlled os the laborer, the optical output of which through the third reflective mirror, the second remote mirror in the entered state and through the fourth translucent mirror is optically connected to the optical inputs of the second laser modulator and the fourth controlled attenuator, the optical input of the second controlled attenuator with the first remote mirror introduced and the output second remote mirror optically coupled by means of a first extension mirror, a first translucent mirror and a fourth translucent of the second mirror with the optical input of the second laser radiation modulator and with the optical input of the fourth controlled attenuator, the control inputs of the second laser generator, the first and second laser radiation modulators, the first, second, third and fourth controlled attenuators are connected to the processing and control unit, the control units are first and the second remote mirrors are connected to the processing and control unit, the output of the third photodetector unit is connected to the processing and control unit. 2. The measurement system according to claim 1, characterized in that the measuring and reference cuvettes in it are equipped with optically transparent windows. 3. The measurement system according to claim 1, characterized in that the measuring cell is connected to the cooling circuit of the nuclear power reactor by means of a bypass pipeline branched from the cooling circuit. 4. The measurement system according to claim 1, characterized in that it uses a laser generator of the ultraviolet wavelength range as the first laser generator. 5. The measurement system according to claim 1, characterized in that the first and second laser generators are configured to tune the wavelength of the generated laser radiation. 6. The measurement system according to claim 1, characterized in that an acousto-optic cell with a control unit connected to the processing and control unit is used as a beam splitter, the optical input of the acousto-optical cell being optically connected to the optical input of the measuring cell and the optical output of the acousto-optical cell being parallel optical connected to the first corner reflector and the optical output of the second fiber adapter. 7. The measurement system according to claim 1, characterized in that the reference cuvette is equipped with a working substance filling unit, equipped with inlet and outlet taps.

Images