WO2021234292A1

WO2021234292A1 - Method and system for continuously monitoring atmospheric radioactive contamination

Info

Publication number: WO2021234292A1
Application number: PCT/FR2021/050889
Authority: WO
Inventors: Gwenaël HOARAU; François GENSDARMES; Grégoire DOUGNIAUX
Original assignee: Electricite De France; Institut De Radioprotection Et De Surete Nucleaire
Priority date: 2020-05-20
Filing date: 2021-05-19
Publication date: 2021-11-25
Also published as: FR3110709B1; FR3110709A1

Abstract

The invention relates to a method for monitoring atmospheric radioactive contamination of a medium (1) implemented using a system (10) for monitoring atmospheric radioactive contamination, the monitoring system (10) comprising a monitor (100) for measuring atmospheric radioactive contamination, AMC below, and a device (200) for counting and classifying in terms of particle size. The method especially comprises steps of measuring, using the device (200) for counting and classifying in terms of particle size, at least one characteristic quantity of particles present in the medium (1) and of determining, from the at least one characteristic quantity, at least one factor k for correcting an activity relative to artificial alpha radiation with respect to an activity related to natural alpha radiation. The invention furthermore relates to a monitoring system (10) allowing such a method to be implemented.

Description

Continuous monitoring method and system for atmospheric radioactive contamination

Technical area

The invention relates to the field of monitoring atmospheric radioactive contamination with the aim of ensuring the radiation protection of workers, monitoring of sites and of discharges.

Thus, more specifically the subject of the invention is a method for monitoring atmospheric radioactive contamination, a method for calibrating a monitoring system for atmospheric radioactive contamination, a system for monitoring atmospheric radioactive contamination and a kit for an atmospheric radioactive contamination. atmospheric radioactive contamination monitoring system.

State of the prior art

In the context of certain industrial sites, such as active nuclear power plants or decontamination and / or dismantling sites of sites dedicated to nuclear power, for example, nuclear power plants, it is necessary to monitor atmospheric radioactive contamination in order to ensure radiation protection of workers during operations that may resuspend the aerosols generated (for example during cutting, welding or decontamination operations) and check the harmlessness of any releases. It is known practice to carry out such monitoring using continuous measurement monitors for atmospheric radioactive contamination, hereinafter referred to as CAM.

A CAM is configured to carry out an atmospheric sample in a medium, such as the air of the aforementioned industrial sites such as decontamination and / or dismantling sites, and to measure at least a first quantity of activity of the atmospheric sample relating to artificial alpha radiation in order to determine a state of contamination of said medium with artificial radionuclides.

By state of contamination of the medium is meant above and in the rest of this document a characteristic of the atmospheric radioactive contamination of the medium. this could be, for example, a measurement of activity relating to artificial alpha radiation, a state of exceeding one or more activity thresholds considered as indicative of a contamination of the environment, or a contamination indicator deduced from from at least a first size of activity.

Such a configuration complies with the international standards of the International Electrotechnical Commission, better known by its acronym IEC for “International Electrotechnical Commission” specifying the test conditions for contamination monitoring devices. However, these standards were established for very precise stationary test conditions with a size dimension of natural radioactive aerosols, i.e. 0.2 μm, and not considering a state of dustiness in the ambient air which are not representative of the characteristics generally observed in environments where basic operations (cutting materials, cleaning dust, etc.) are carried out. These differences in characteristics in terms of size and concentration induce measurement biases mainly due to the rapid accumulation of a large quantity of particles on the CAM sampling filter not considered by the standard and which may therefore be at the expense of origin, due to the degradation of the energy spectrum which results from it, of erroneous detections of the state of contamination of the medium.

It will be noted that mention is made above and in the rest of this document of an activity relating to artificial alpha radiation and an activity relating to natural alpha radiation, respectively. This first activity relating to artificial alpha radiation corresponds to the activity linked to elements little or not present in the environment in the natural state and which are therefore linked to a process of human origin, such as for example the isotope 239 of plutonium, ²³⁹ Pu, and the isotope 241 of americium, ²⁴¹ Am. The activity relating to natural alpha radiation corresponds to the activity linked to elements ubiquitous in the environment in the natural state, that is that is to say essentially the isotope 222 of radon ²²² Rn and its solid descendants ( ²¹⁸ Po, ²¹⁴ Po). It will be noted that it is possible to distinguish the activity relating to artificial alpha radiation from the activity relating to natural alpha radiation by means of energy windows of the radiation considered, these activities being predominant in distinct energy windows (the natural alpha radiations exhibit higher energy than those of artificial alpha radiations).

In order to take into account the presence of these aerosols and thus to detect or not the states of contamination, two solutions are currently implemented.

The first solution consists in equipping the CAM with a selector in order to remove particles of a size greater than a given dimension. This solution makes it possible to prevent the activity measurement from being degraded by the presence of relatively “large” particles (generally greater than 10 μm). However, if this first solution is free from the presence of large particles and makes it possible to obtain a representative state of contamination with regard to the particles of smaller sizes, it is not suitable in the case where the particles large sizes, that is to say of a dimension greater than said given dimension, are themselves at the origin of artificial alpha radiation.

It is noted that, by particles, in the absence of a specification according to which they are alpha particles, is meant the particles composing the aerosols and by abuse of language called dust which are therefore distinct from the alpha particles which are ionizing radiation.

The second solution consists in correcting the influence of the increased activity relating to natural alpha radiation, measured in the window dedicated to the measurement of artificial alphas, linked to the presence of these particles by means of a correction factor k. A CAM according to this second solution is further configured to measure at least a second quantity of activity of the atmospheric sample relating only to natural alpha radiation and to determine a state of radioactive contamination of the medium with artificial radionuclides from the first quantity of activity after compensation for natural activity on the basis of at least one correction factor k and at least one second activity quantity. This therefore results, with this second solution, in taking into account the natural activity making it possible to obtain a more realistic state of the artificial contamination of the environment.

However, this second solution is still subject, depending on the particle size and the aerosol concentration, to obtaining contamination states. wrong from the middle. This is not acceptable since such an erroneous state of contamination can lead to the shutdown of the industrial sites under surveillance and of the sites which can take place there without it being necessary, a situation which is penalizing for the operator of the industrial site in question.

Thus, at the present time, there is no suitable solution to allow monitoring of a medium when it is subjected to concentrations or aerosol sizes different from that recommended in the normative tests for the compensation for natural radioactivity.

Disclosure of the invention

The invention aims to remedy these drawbacks and thus aims to provide a method for monitoring the artificial radioactivity of a medium which is less subject, vis-à-vis current monitoring methods, to the provision of status. of erroneous contamination of said medium.

To this end, the invention relates to a method for monitoring the atmospheric radioactive contamination of a medium implemented using a monitoring system for atmospheric radioactive contamination, the monitoring system comprising a monitor for measuring the radioactive contamination. atmospheric, hereinafter CAM, and a device for counting and classifying by particle size, the method comprising the following steps: carrying out, by the CAM, of an atmospheric sample in the medium, measurement, from the counting device and classification by size of the particles, of at least one characteristic quantity of the particles present in the medium, determination, from the at least one characteristic quantity, of at least one correction factor k of an activity relating to the artificial alpha radiation with respect to an activity relating to natural alpha radiation, measurement, by the CAM, of at least a first gross quantity of activity atmospheric sampling relating to artificial alpha radiation and at least a second activity quantity of atmospheric sampling relating to natural alpha radiation, determination of a state of contamination of the medium with artificial radionuclides from the first gross activity quantity after compensation for the natural activity from the at least one correction factor k and the at least one second quantity activity.

With such a method, it is possible to precisely take into account the background noise, linked to the natural activity in the window of artificial alpha, in the medium and taken by the CAM, whatever the configuration of said aerosol. Indeed, with the measurement offered by the particle size counting and classification device, it is possible to know the characteristics of the aerosol and to provide a correction factor k adapted to these characteristics. It follows that the state of contamination of the medium determined from the method is more precise than that determined with the methods of the prior art and that the risks of detecting an erroneous contamination of the medium is particularly reduced with respect to these same processes. It will also be noted that such a method allows, in accordance with the regulations in force in France, continuous monitoring of the medium.

By configuration of the aerosol it is understood, above and in the rest of this document, the median diameter of these particles, the quantity of these particles per volume of air, or even a mass of these particles per volume of air . It may also be noted that in this configuration, account can also be taken of a size distribution of these same particles.

The particle size counting and classifying device is a particle counter selected from the group consisting of optical type particle counters, particle counters based on electrical charging of particles, the size counting and classifying device particles preferably being a particle counter of the optical type.

Such a device has the advantage of providing a reliable measurement of the configuration of the aerosol, this in particular for a relatively low cost in the case of an optical type particle counter. The at least one characteristic quantity may comprise a quantitative quantity of the particles, such as a concentration, and a dimensional quantity of said particles, such as a median diameter of the particles.

Such quantities allow a good qualification of the configuration of the aerosol and thus a determination, using for example an experimentally established database, of the correction factor k adapted to the situation.

The first gross activity quantity can be an activity quantity, such as a number of alpha decays during a given period of time in a first energy range corresponding to the artificial alpha radiations, and the second activity quantity being a quantity of activity, such as a number of alpha decays during a given period of time, in a second energy range corresponding to natural alpha radiations, said second energy range being outside an energy range corresponding to artificial alpha radiation.

The state of contamination of the determined medium can be selected from the group comprising: a first corrected contamination quantity determined by a correction of the first contamination quantity from the second contaminator quantity and the correction factor k, a variable to at least a first and a second state corresponding to an overshoot or not of a contamination threshold, this threshold overshoot being determined on the basis of a first corrected contamination quantity determined by a correction of the first contamination quantity from of the second contaminator quantity and of the correction factor k, a variable with at least a first and a second state corresponding to an overshoot or not of a contamination threshold, this threshold overshoot being determined on the basis of the first quantity gross contamination, the value of said threshold being a corrected value from the second contaminator quantity and the fa correction factor k.

The step of determining, from the at least one characteristic quantity, the at least one correction factor k is a step consisting in comparing the at least one characteristic quantity to a database in order to determine the correction factor k suitable for the range of characteristic quantities in which the at least one characteristic quantity is located.

With such a database, it is easy to determine the correction factor k regardless of the aerosol configuration determined from the particle counting device.

The invention further relates to a calibration method for an atmospheric radioactive contamination monitoring system, the monitoring system comprising an atmospheric radioactive contamination measurement monitor, hereinafter CAM and a particle counting device, the calibration method comprising: subjecting the monitoring system to at least one medium exhibiting a respective known artificial activity and, for each medium of known artificial activity, at least two given aerosol configurations each exhibiting a known natural activity, the two aerosol configurations exhibiting at least one distinct characteristic quantity, for each medium of artificial activity and for each aerosol configuration, realization, by the CAM, of an atmospheric sample in the, and measurement, for each sample, of d '' at least a first gross activity quantity of atmospheric sampling relating to artificial alpha radiation and at least a second activity quantity of the atmospheric sample relating to natural alpha radiation, for each medium of artificial activity and for each aerosol configuration, measurement, from the device for counting and classifying the particles in size , of at least one characteristic quantity of the particles present in the medium, for each aerosol configuration associated with the at least one characteristic quantity, determination, from the artificial activity expected for said medium of artificial activity, of the first gross activity quantities, of the second quantities activity, of a respective correction factor k of an activity relating to artificial alpha radiations vis-à-vis an activity relating to natural alpha radiations.

Such a method makes it possible to obtain a suitable calibration for a monitoring system in accordance with the invention. The invention further relates to a system for monitoring atmospheric radioactive contamination in a medium comprising: a monitor for measuring atmospheric radioactive contamination, hereinafter CAM, the CAM being configured to take an atmospheric sample from the medium and to measure at least a first gross activity quantity of atmospheric sampling relating to artificial alpha radiation and at least a second activity quantity of atmospheric sampling relating to natural alpha radiation, the CAM being further configured for a state of contamination of the medium in artificial radionuclides from the first gross activity quantity after compensation of the natural activity from the at least one correction factor k and from the at least one second activity quantity, the monitoring system of atmospheric radioactive contamination further comprising: a device for counting and classifying the size of the particles configured to measure at least one characteristic quantity of the particles present in the medium, the monitoring system being configured so that the correction factor k is determined from the at least one characteristic quantity measured by the counting device.

Since such a monitoring system according to the invention is able to implement a monitoring method according to the invention, it makes it possible to obtain the advantages which are linked to this same method. In addition, such more than such a device method, in accordance with the regulations in force in France, continuous monitoring of the medium.

The monitoring system may include a processing unit configured to communicate with the particle counting device to retrieve water. at least one characteristic quantity measured by the counting device and for determining the correction factor k from said measured characteristic quantity, said processing unit being further configured to supply the determined correction factor k to the CAM.

Brief description of the drawings

The present invention will be better understood on reading the description of exemplary embodiments, given purely as an indication and in no way limiting, with reference to the appended drawings in which: FIG. 1 illustrates a schematic view of a monitoring system of atmospheric radioactive contamination of a medium, FIG. 2 illustrates a functional diagram of the monitoring system, FIG. 3 illustrates a flowchart of a monitoring method implemented by means of such a monitoring system, FIG. 4 illustrates a flowchart of a method of calibrating such a monitoring system, FIG. 5A graphically illustrates a first example of subjecting a monitoring system in an uncontaminated medium to a first aerosol configuration, the graph shown in both the evolution of the mass concentration of particles and the volume activity corresponding to the artificial alpha radiation as a function of the respective measured time ment by the particle counting device and the CAM, FIG. 5B illustrates graphically and respectively the signal measured by the particle counting device, the activity corresponding to the artificial alpha radiation measured by the CAM, the background noise estimated by the CAM from a standard correction factor k, a decision threshold corresponding to a contaminated state determined by the CAM for a standard correction factor k and a detection limit of the CAM for a standard correction factor k, this as a function of time for this first example of submission, FIG. 5C illustrates graphically and respectively the signal measured by the particle counting device, the activity corresponding to the artificial alpha radiation measured by the CAM, the background noise estimated by the CAM from a correction factor k adapted in function of the signal measured by the particle counting device, a decision threshold corresponding to a contaminated state determined by the CAM for an adapted correction factor k and a detection limit of the CAM for an adapted correction factor k, this as a function of time for this first example of submission, FIG. 6A graphically illustrates a second example of submission of a monitoring system in an uncontaminated medium to a first aerosol configuration, the graph showing both the evolution of the concentration particle mass and volume activity corresponding to artificial alpha radiation as a function of time measured respectively by the counting device age and classification in particle size and the CAM, FIG. 6B illustrates graphically and respectively the signal measured by the device for counting and classification in particle size, the activity corresponding to the artificial alpha radiation measured by the CAM, the noise background estimated by the CAM from a standard correction factor k, a decision threshold corresponding to a contaminated state determined by the CAM for a standard correction factor k and a detection limit of the CAM for a standard correction factor k, this as a function of time for this second example of submission, FIG. 6C illustrates graphically and respectively the signal measured by the device for counting and classifying in particle size, the activity corresponding to the artificial alpha radiation measured by the CAM, the background noise estimated by the CAM from a correction factor k adapted as a function of the signal measured by the counting and classing device ification in particle size, a decision threshold corresponding to a contaminated state determined by the CAM for an adapted correction factor k and a detection limit of the CAM for an adapted correction factor k, this as a function of time for this second example submission.

Identical, similar or equivalent parts of the different figures bear the same numerical references so as to facilitate the passage from one figure to another. The different parts shown in the figures are not necessarily on a uniform scale, to make the figures more readable.

The different possibilities (variants and embodiments) must be understood as not being mutually exclusive and can be combined with one another.

Description of the embodiments

FIG. 1 illustrates a monitoring system 10 for atmospheric radioactive contamination according to the invention for monitoring the atmosphere of a medium, such as a decontamination and / or dismantling site of an industrial site liable to exhibit radioactive contamination. . With such a system 10, this monitoring can be carried out, if necessary and in accordance with the regulations in force in France, continuously.

Such a monitoring system comprises, as illustrated in FIG. 1: a measuring monitor 100 of atmospheric radioactive contamination, hereinafter CAM, the CAM 100 being configured to take an atmospheric sample in the medium 1 and to measure at least one first gross activity quantity of atmospheric sampling relating to artificial alpha radiation and at least a second activity quantity of atmospheric sampling relating to natural alpha radiation, the CAM 100 being further configured for a state of contamination of the medium 1 in artificial radionuclides from the first gross activity quantity after compensation of the natural activity from the at least one correction factor k and from the at least one second activity quantity, a device for counting and particle size classification 200 configured to measure at least one characteristic quantity of the particles present in the medium 1, a trait unit ement 300, shown only in FIG. 2, configured to communicate with the particle counting and classifying device 200 in order to retrieve the at least one characteristic quantity measured by the particle counting and classifying device and to determine the factor of correction k from said measured characteristic quantity, the processing unit is further configured to supply the determined correction factor k to the CAM.

The CAM 100 according to this first embodiment is a CAM 100 according to the prior art according to the second solution described. Thus, according to the principle of

5 operation of such a CAM 100 and as illustrated in the functional diagram of FIG. 2, a CAM is more precisely shaped for:

-110- take an atmospheric sample in the medium 1 this, for example, by passing a predefined volume of air through a filter acting as a deposit surface for the sample,

10 -120- carry out a measurement of the alpha radiation emitted by the sample deposited on the filter in order to obtain a measurement of the activity of the sample, 125 determine from said measurement of an activity of the atmospheric sample relating to artificial alpha radiation, this activity may correspond to a count linked to alpha particles received per unit of time in a

15 first energy window corresponding to artificial alpha radiation, is a first gross quantity of activity,

-121- determine from the measurement of an activity of the atmospheric sample relating to natural alpha radiation, this activity being able to correspond to a number of alpha particles received per minute in a second

20 energy window corresponding only to natural alpha radiation, is a second activity magnitude,

-122- estimate from the second activity quantity and the correction factor k supplied by the processing unit 300, of a correction value for the natural activity in the first energy window,

25 126 compensate the first gross activity quantity with the activity correction value, which compensation can be achieved either by subtracting the natural activity correction value in the first energy window from the first gross quantity of activity, or by using this correction value for natural activity as a noise level to determine a threshold for the first gross activity quantity at

30 from which contamination of medium 1 is detected, 130 determination of a state of contamination of the medium 1, this determination possibly corresponding to the provision of a corrected measurement of the activity linked to radiation, for example by a dedicated display or by a transmission to a central monitoring station centralizing several monitoring systems. monitoring, and / or by determining whether the first activity quantity has been exceeded, whether this is raw or corrected, of a threshold corresponding to contamination of the medium 1 is exceeded, the CAM 100 then being configured, for example , for, for example an audible or visual alarm.

It will be noted that, of course and in accordance with the CAM of the prior art, the CAM 100 according to the invention can be adapted to measure activities linked to ionizing particles other than alphas, such for example beta particles. Likewise, if it is described above that the CAM 100 is suitable for measuring only a single gross quantity of activity linked to alpha

The particle size counting and classification device 200 is arranged in the medium 1 in order to characterize the presence of aerosol in the air and thus allow, according to the principle of the invention, a correction of the measurements carried out by the CAM. 100. So that the device for counting and classifying in particle size 200 makes it possible to characterize the configuration of the aerosol to which the CAM 100 is subjected, the device for counting and classifying in particle size 200 is positioned as close as possible to the CAM 100. Thus, in the present embodiment and as illustrated in Fig. 1, the particle counting and classifying device 200 is integrated into the CAM 100 with an arrangement in which the counting device 200 intercepts a part. of the air flow taken by the CAM 100. Of course, this particularly advantageous configuration is provided only by way of example, other arrangements of the counting device e t particle size classification 200 joined or disjointed from the CAM 100 are perfectly conceivable without departing from the scope of the invention.

In the present embodiment, the particle size counting and classification device 200 is an optical device based on the scattering of light by the particles. Of course, if such an optical particle size counting and classification device 200 is advantageous in the context of the invention, other device for counting and classifying in particle size, such as counting based on the particle size. electric charges carried by the particles and their size classification by inertial or electrostatic effect (or particle counters based on an electric charge of the particles), can be envisaged without departing from the scope of the invention.

According to the invention, the particle size counting and classification device 200 is, according to the functional diagram of FIG. 2, configured to: 210 take a sample of a volume of air from the medium 1, 220 determine to at least one characteristic quantity of the particles found in the volume of air sampled, this or these characteristic quantities possibly being a quantitative quantity of the particles, such as a concentration, and a dimensional quantity of said particles, such as a median diameter of the particles particles.

It will be noted that, according to one possibility of the invention, the above step 201 can be a common step with the CAM when the particle size counting and classification device 200 is integrated into the CAM, the measurement of the counting device and particle size classification 200 then being carried out on at least part of the volume of air taken by the CAM.

The particle size counting and classification device 200 is preferably configured to implement steps -201- and -202- continuously so as to allow continuous monitoring of the aerosol to which the CAM 100 is subjected, but can also be configured to perform these steps at regular time intervals in order to know the evolution of the aerosol to which the CAM 100 is subjected. According to a variant of the invention, it is also conceivable that the counting device and particle size classification 200 is configured to perform these steps on an ad hoc basis.

Note that in the present embodiment, the particle size counting and classifying device 200 is configured to determine both a particle concentration and a median particle diameter. Of course, other configurations of the particle size counting and classification device 200 can be envisaged without departing from the scope of the invention. Thus, for example, the particle size counting and classifying device 200 may be adapted to provide a number, mass, or number of electric charges (per particle) of particles per unit volume for several particle size ranges.

The characteristic size (s) of the particles of the medium 1 are communicated to the processing unit 300 by the device for counting and classifying the particles in size 200.

The processing unit 300 is configured so as, as illustrated in the functional diagram of FIG. 2: 310 to determine, from the characteristic quantity (s) supplied by the particle size counting and classification device 200, the factor of correction k of an activity relating to artificial alpha radiations vis-à-vis an activity relating to natural alpha radiations, 320 transmitting the determined k factor to the CAM in order to adequately compensate for the part of the activity related to alpha radiations natural in the first magnitude of gross activity.

This determination of the correction factor can be carried out, for example, by a comparison of the characteristic quantity or quantities supplied by the device for counting and classifying in particle size with a database associating ranges of characteristic quantity with a factor of correction k. As a variant, the processing unit can be adapted to calculate such a correction factor from said characteristic quantity or quantities and from a mathematical relationship established beforehand.

In the present embodiment, in the case where the characteristic quantities provided by the particle size counting and classification device are a concentration and a median diameter, the processing unit 300 can determine the correction factor from 'a two-entry database which can be presented in the form of the following table:

In this table, the columns correspond to a range of median diameters and the rows correspond to a range of particle concentrations. Thus, for example, for particles with a concentration C of between Cl and C2 and having a median diameter less than dl, the processing unit will select the value k2 _{, i} .

It will be noted, as will be described in the context of the method for calibrating a monitoring system, that the processing unit 300 can also be configured to allow the constitution of this database. According to this possibility, which could for example be implemented in the factory as part of the assembly of the monitoring system, the processing unit 300 can be configured to calculate the correction factor for a given aerosol configuration from the measurements. performed by the CAM 100 and, optionally, the particle size counting and classification device 200.

According to one possibility of the invention, if the processing unit 300 is described in the present embodiment, as a separate unit from the CAM 100, in particular to allow adaptation of the monitoring systems of the prior art, it is also It can be envisaged that it is directly integrated into the CAM 100 in the form, for example, of a sub-unit of the control electronics of the CAM 100.

According to another possibility of the invention, it is also conceivable, this to facilitate the adaptation of a monitoring system of the prior art, without departing from the scope of the invention, that the processing unit 300 is integrated into the particle size counting and classifying device 200 in the form, for example, of a subunit of the control electronics of the particle size counting and classifying device 200.

Alternatively, the processing unit 330 can be provided by means of a program product installed in a computer acting as a computer. acquisition system for the CAM and for the particle size counting and classification device without departing from the scope of the invention.

Thus, according to the two possibilities above, the invention also relates to a kit for a CAM monitoring system 100 comprising a counting and monitoring device.

5 particle size classification 200 and a processing unit 300 in order to allow adaptation of a monitoring system according to the prior art.

A monitoring system 10 according to the invention is suitable for implementing a method for monitoring a medium 1. Such a monitoring method comprises, as illustrated in FIG. 3, the following steps:

10 501 realization, by the CAM 100, of an atmospheric sample in the medium 1 by, for example, by passing a predefined volume of air through a filter acting as a deposit surface for the sample, 502 measurement , by the CAM 100, of the activity of the atmospheric sample, for example by carrying out a measurement of the alpha radiation emitted by the deposited sample

15 on the filter in order to obtain a measurement of the activity of the sample, 511 in parallel and / or prior to steps 501 and 502 realization by the device for counting and classifying in size of particles 200 of a sample of a volume d air of the medium 1 and determination, by this same device for counting and classifying the size of particles 200, of at least one quantity characteristic of

20 particles located in the volume of air sampled, this or these characteristic size (s) possibly being a quantitative quantity of the particles, such as a concentration, and a dimensional quantity of said particles, such as a median diameter of the particles, 512 determination, from the characteristic quantity (s) supplied by the particle size counting and classification device 200, the factor of

25 correction k of an activity relating to artificial alpha radiations vis-à-vis an activity relating to natural alpha radiations, 503 once steps 502 and 512 have been carried out, determination from said measurement of an activity of the atmospheric sampling relating to artificial alpha radiation, this activity being able to correspond to a number of alpha particles received per minute in a first energy window corresponding to artificial alpha radiation, is a first gross activity quantity, 504 determined from the measurement of an activity of the atmospheric sample relating to natural alpha radiation, this activity possibly corresponding to a number of alpha particles received per minute in a second energy window corresponding only to natural alpha radiation, is a second activity quantity, 505 estimation from the second activity quantity and the correction factor k previously obtained, d 'a correction value for the natural activity in the first energy window, 506 estimation from the second activity quantity and the determined correction factor k, of a correction value for the natural activity in the first energy window, 507 compensation of the first gross activity quantity with the activity correction value, this compensation being able to be re alized either by subtracting the correction value for natural activity in the first energy window from the first gross activity quantity, or by using this correction value for natural activity as a noise level to determine a threshold of first magnitude.

The monitoring system 10 according to the invention is also suitable for implementing a method for calibrating such a system, as illustrated in FIG. 4, the following steps: 601 providing a plurality of representative aerosol configurations ranges of interest of at least one characteristic quantity of particles, 602 supplying at least one medium 1 exhibiting a respective known artificial activity and subjecting the monitoring system 10 to said medium 1, 603 submitting medium 1 and to the monitoring system monitoring at each of the aerosol configurations, taking a respective sample by the CAM for each aerosol configuration, and measuring, for each sample, at least a first gross quantity of activity of the atmospheric sample relating to alpha radiation artificial and at least a second activity quantity of the atmospheric sampling relative to natural alpha radiation, 604 in parallel with the activity measurement by the CAM, when submitting medium 1 and to the monitoring system at each of the configurations d 'aerosol, measurement, from the particle size counting and classification device 200 and for each aerosol configuration, of at least one characteristic quantity of the particles present in the medium 1, 605 for each aerosol configuration associated with at least one characteristic range, determination, from the artificial activity expected for said medium of artificial activity, of the first gross activity quantities, of the second activity quantities, of a correction factor k respective of an activity relating to artificial alpha radiations vis-à-vis an activity relating to natural alpha radiations, 606 from the correction factors k, formation of a low e of data allowing the determination, from at least one characteristic quantity, of at least one correction factor k of an activity relating to artificial alpha radiations vis-à-vis an activity relating to natural alpha radiations .

It will be noted that such a calibration operation can be carried out either in the factory, during the manufacture of the monitoring system 10, or by the user, for example during the adaptation of a monitoring system of the art. prior by adding a particle size counting and classification device 200 and a processing unit 300.

In order to illustrate an example of the implementations of the invention and to show the advantage of the invention over a monitoring system 10 according to the prior art, the inventors have submitted a monitoring system according to the invention to two different aerosol configurations and compared, from the measurements obtained by the CAM 100, the states of contamination of the medium 1 which would be obtained by a monitoring system of the prior art and a monitoring system according to the invention using a correction factor adapted as a function of the measurements of the particle size counting and classification device 200.

In the context of this comparison, the inventors used a monitoring system comprising: an ABPM 203M atmospheric radioactive contamination measurement monitor (CAM) marketed by the company MIRION Technologies ™, an optical particle size counting and classification device Grimm model 1.109 marketed by the company Grimm Aérosol technik GMbH & co ™ .

FIG. 5A illustrates graphically the evolution of the mass concentration of particles (C - 701) and the artificial alpha volume activity (A _a-art - 702) respectively measured by the CAM 100 and the device for counting and classification in particle size 200 when subjected to the first aerosol composed of particles having a median diameter of 5.6 µm.

FIG. 5B graphically illustrates the processing of the measurement carried out by the CAM by a monitoring system according to the prior art, this for a correction factor k = 0.09 conventionally used by showing respectively the raw counting measurement of artificial alpha ( c_a art - 711) supplied by the CAM 100, the particle concentration (C - 712) supplied by the particle size counting and classification device 200, the background noise (c_a art - 713) of the count measurement gross artificial alpha corresponding to natural alpha estimated from the correction factor k = 0.09, the decision threshold (c_a art - 714), corresponding to a suspected contaminated state of the medium 1 determined from the factor of correction k = 0.09 and the detection limit (c_a art - 715) of the surveillance system determined from the correction factor k = 0.09 corresponding to a strong suspicion of a contaminated state of medium 1. Note that Usually, the detection limit corresponds to a double probability of contamination with respect to the decision threshold.

It can be seen that in such a configuration in accordance with the prior art, a monitoring system detects an artificial alpha activity 711 regularly exceeding the detection threshold 714 and therefore a suspected contaminated state of the medium to be monitored.

FIG. 5C graphically illustrates the processing of the measurement carried out by the CAM by a monitoring system according to the invention, this for an adapted correction factor k provided by the processing unit 300 by respectively showing the raw count measurement of alpha artificial (c_a art - 721) supplied by the CAM 100, the concentration of particles (C - 722) supplied by the device for counting and classifying in particle size 200, the background noise (c_a art - 723) of the raw artificial alpha count measurement corresponding to the natural alpha estimated from the adapted correction factor, the decision threshold (c_a art - 724), corresponding to the suspicion of a contaminated state of the medium 1 determined from the adapted correction factor and the detection limit (c_a art - 725) of the monitoring system determined from the adapted correction factor.

Thus, with a suitable correction factor, the raw alpha activity 721 follows, as it should, the estimated background 723. As a result, the gross alpha activity 721 remains well below the decision threshold and no suspicion of a contaminated state of the medium is identified in the absence of activity actually linked to artificial elements.

FIG. 6A illustrates graphically the evolution of the mass concentration of particles (C - 731) and the artificial alpha volume activity (A _aa r _t - 732) respectively measured by the CAM 100 and the device for counting and classification in particle size 200 when subjected to the second aerosol composed of particles with a median diameter of 7.9 µm.

FIG. 6B graphically illustrates the processing of the measurement carried out by the CAM by a monitoring system according to the prior art, this for a correction factor k = 0.09 conventionally used by showing respectively the raw counting measurement of artificial alpha ( c_a art - 741) supplied by the CAM 100, the particle concentration (C - 742) supplied by the particle size counting and classification device 200, the background noise (c_a art - 743) of the count measurement raw artificial alpha corresponding to natural alpha estimated from the correction factor k = 0.09, the decision threshold (c_a art - 744), corresponding to a contaminated state of the medium 1 determined from the correction factor k = 0.09 and the detection limit (c_a art - 745) of the monitoring system determined from the correction factor k = 0.09.

It can be seen that in such a configuration in accordance with the prior art, a monitoring system detects an artificial alpha activity 741 remaining above the decision threshold and even sometimes exceeding the detection limit corresponding to a strong suspicion. contaminated state of the environment.

FIG. 6C graphically illustrates the processing of the measurement carried out by the CAM by a monitoring system according to the invention, this for an adapted correction factor k provided by the processing unit 300 showing respectively the raw counting measurement of artificial alpha (c_a art - 751) provided by the CAM 100, the particle concentration (C -752) provided by the counting and classification device in particle size 200, the background noise (c_a art - 753) of the raw artificial alpha count measurement corresponding to the natural alpha estimated from the adapted correction factor, the decision threshold (c_a art - 754), corresponding to a suspected contaminated state of the medium 1 determined from the adapted correction factor and the detection limit (c_a art - 755) of the surveillance system determined from the adapted correction factor.

Thus, with an adapted correction factor k, the raw alpha activity 751 remains close to the background noise 752 throughout the duration of the measurement. Therefore, if, as for the prior art, the raw alpha activity passes four times above the decision threshold, this detection of a suspected contaminated state is only fleeting and is not constant unlike to what is observed for the prior art.

Thus, in the context of these two aerosol configurations, a significant improvement is observed concerning the reliability of the detection of a suspected contaminated state of medium 1 with respect to the prior art.

Claims

1. A method of monitoring the atmospheric radioactive contamination of a medium (1) implemented from a monitoring system (10) of atmospheric radioactive contamination, the monitoring system (10) comprising a measurement monitor ( 100) of atmospheric radioactive contamination, hereinafter CAM, and a device for counting and classifying by particle size (200), the method comprising the following steps: carrying out, by the CAM (100), of an atmospheric sample in the medium (1), measurement, from the particle size counting and classification device (200), of at least one quantity characteristic of the particles present in the medium (1), determination, from the at least one characteristic quantity, of at least one correction factor k of an activity relating to artificial alpha radiations vis-à-vis an activity relating to natural alpha radiations, measurement, by the CAM (100), of at least a first size gross activity of the atmospheric sample relating to artificial alpha radiation and of at least a second activity quantity of the atmospheric sample relating to natural alpha radiation, determination of a state of contamination of the medium (1) with artificial radionuclides from the first gross activity quantity after compensation for the natural activity on the basis of the at least one correction factor k and the at least one second activity quantity.

The monitoring method according to claim 1, wherein the particle size counting and classification device (200) is a particle counter selected from the group comprising optical type particle counters, particle counters based on. electrical charging of the particles, the device particle size counting and classification (200) preferably being a particle counter of the optical type.

3. Monitoring method according to claim 1 or 2, wherein the at least one characteristic quantity comprises a quantitative quantity of the particles, such as a concentration, and a dimensional quantity of said particles, such as a median diameter of the particles.

4. Monitoring method according to any one of claims 1 to 3 wherein the first gross activity quantity is an activity quantity, such as a number of alpha decays during a given period of time in a first range d. 'energy corresponding to artificial alpha radiation, and in which the second activity quantity is an activity quantity, such as an alpha decay number during a given period of time, in a second energy range corresponding to alpha radiation natural, said second energy range being outside an energy range corresponding to artificial alpha radiation.

5. Monitoring method according to any one of claims 1 to 4, wherein the state of contamination of the medium (1) determined is selected from the group comprising: a first corrected contamination quantity determined by a correction of the first quantity of contamination from the second contaminator quantity and from the correction factor k, a variable with at least a first and a second state corresponding to an overshoot or not of a contamination threshold, this threshold overshoot being determined on the basis a first corrected contamination quantity determined by a correction of the first contamination quantity from the second contaminator quantity and the correction factor k, a variable with at least one first and a second state corresponding to an overshoot or not a contamination threshold, this threshold being exceeded determined on the basis of the first gross contamination quantity, the value of said threshold being a value corrected from the second contaminator quantity and from the correction factor k.

6. Monitoring method according to any one of claims 1 to 5, wherein the step of determining, from the at least one characteristic quantity, the at least one correction factor k is a step consisting in comparing the at least one characteristic quantity with a database in order to determine the correction factor k suitable for the range of characteristic quantities in which the at least one characteristic quantity is located.

7. Calibration method for a monitoring system (10) of atmospheric radioactive contamination, the monitoring system (10) comprising a measuring monitor (100) of atmospheric radioactive contamination, hereinafter CAM and a counting device. and particle size classification (200), the calibration method comprising: subjecting the monitoring system (10) to at least one medium (1) having a respective known artificial activity and, for each medium (1) of known artificial activity, at at least two given aerosol configurations each exhibiting a known natural activity, the two aerosol configurations exhibiting at least one distinct characteristic quantity, for each medium (1) of artificial activity and for each configuration of aerosol, realization, by the CAM (100), of an atmospheric sample in the medium (1), and measurement, for each sample, of at least a first gross quantity of activity of the sample atmospheric relating to artificial alpha radiation and at least a second activity quantity of the atmospheric sampling relating to natural alpha radiation, for each medium (1) of artificial activity and for each aerosol configuration, measurement, from the device counting and classification by size of particles (200), of at least one characteristic quantity of the particles present in the medium (l), for each aerosol configuration associated with the at least one characteristic quantity, determination, from the artificial activity expected for said media of artificial activity, of the first gross activity quantities, of the second activity quantities, of a respective correction factor k of an activity relating to artificial alpha radiation vis-à-vis an activity relating to natural alpha radiation.

8. System for monitoring (10) atmospheric radioactive contamination in a medium (1) comprising: a measuring monitor (100) of atmospheric radioactive contamination, hereinafter CAM, the CAM (100) being configured to take a sample. atmospheric sample in the medium (1) and to measure at least a first gross activity quantity of atmospheric sampling relating to artificial alpha radiation and at least a second activity quantity of atmospheric sampling relating to natural alpha radiation, the CAM ( 100) being further configured for a state of contamination of the medium (1) with artificial radionuclides from the first gross activity quantity after compensation for the natural activity from the at least one correction factor k and from the at least one second activity quantity, the monitoring system (10) for atmospheric radioactive contamination being characterized in that it further comprises: a counting device ge and particle size classification (200) configured to measure at least one characteristic quantity of the particles present in the medium (1), and in that it is configured so that the correction factor k is determined from the at least one characteristic quantity measured by the particle size counting and classification device (200).

9. The monitoring system (10) for atmospheric radioactive contamination according to claim 8, wherein the monitoring system comprises a monitoring unit. process (300) configured to communicate with the particle counting and particle sizing device (200) to retrieve the at least one characteristic quantity measured by the particle counting and classifying device and to determine the correction factor k from said measured characteristic quantity, and wherein said processing unit is further configured to provide the determined correction factor k to the CAM.

10. Kit for a monitoring system (10) of atmospheric radioactive contamination comprising a measuring monitor (100) of atmospheric radioactive contamination, hereinafter CAM, the CAM (100) being configured to carry out an atmospheric sample in the medium. (1) and to measure at least a first gross activity quantity of atmospheric sampling relating to artificial alpha radiation and at least a second activity quantity of atmospheric sampling relating to natural alpha radiation, the CAM (100) being in further configured for a state of contamination of the medium (l) with artificial radionuclides from the first gross activity quantity after compensation for the natural activity from at least one correction factor k and from at least a second size of activity,

The kit being characterized in that it comprises - a device for counting and classifying in size of particles (200) configured to measure at least one quantity characteristic of the particles present in the medium (1), a processing unit (300) configured to provide the CAM (100) with a correction factor k determined from the at least one characteristic quantity measured by the particle counting and classifying device (200).