JPH01102395A - Sludge height measurement on steam generator tube plate - Google Patents

Abstract

PURPOSE:To measure sludge height at any time by utilizing that rapid temperature gradient is produced in temperature profile and detecting the height of deposing sludge at the boundary of the depositing sludge and a liquid phase. CONSTITUTION:A bar temperature measuring instrument 13 is set in parallel with a conduction tube 3 on a tube plate 4 and a plurality of sensors 13a are axially attached to the measuring instrument 13 at regular intervals above the tube plate 4. Temperature distribution profile can be obtained by the measuring instrument 13 on the tube plate 4. Whenever the temperature distribution profile is always observed and production of the temperature gradient is detected, the height of depositing sludge can be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the invention] (Industrial field of application) The present invention is directed to the use of steam generators that are deposited on tube sheets and eventually transmitted during operation of steam generators used in pressurized water nuclear reactors. This invention relates to a method for measuring the height of sludge on a steam generator tube plate, which can measure the height of sludge that causes corrosion of heat tube materials at any time.

(Prior Art) In a pressurized water reactor, high-temperature, high-pressure water generated in the reactor is converted into steam by a steam generator, and the steam is supplied to a steam turbine that drives a generator.

FIG. 4 shows an example of a conventional steam generator of this kind. An inner cylinder 2 is housed concentrically in the small diameter part of a cylindrical container 1 with a large diameter at the upper end. A tube plate 4 is provided to support the ends of a large number of inverted U-shaped heat exchanger tubes 3. A large number of inverted U-shaped heat exchanger tubes 3 in the inner cylinder 2 are arranged so that the curved portions of their tops are aligned, each of their legs is on a line parallel to the diameter of the tube plate 4, and supported by a support 5. ing. Also, in the large diameter part at the top of the container 1, there is a separator 6 for separating air and water.
A dryer 7 for drying the separated steam is provided, and a primary water inlet 8 is provided at the lower end of the container 1 to supply primary water to the tube sheet 4 in the inner cylinder 2, and a primary water inlet 8 for supplying primary water to the tube sheet 4 in the inner cylinder 2 also allows the primary water to flow out from the tube sheet 4. A primary water outlet 9 is provided for each water outlet. In addition, a secondary water outlet 10 is provided on the side surface of the upper end of the container 1, and a steam outlet 11 is provided in the center of the upper end surface.
are provided for each. Note that a downcomer 12 is formed between the container 1 and the inner cylinder 2.

In the conventional steam generator having the above configuration, steam is generated in the following manner. That is, high-temperature, high-pressure water generated in the reactor enters the vessel 1 from the primary water inlet 8 at the bottom of the vessel 1 of the steam generator, and enters the vessel 1 through a number of inverted U-Us fixed to the tube plate 4.
It flows inside the shape heat exchanger tube 3 and flows out from the primary water outlet 9. Low-temperature secondary water enters the container 1 from the secondary water inlet 10 on the upper side of the container 1, flows down the downcomer 12, enters the inner cylinder 2 via a passage provided above the tube plate 4, and enters the inner cylinder 2. It ascends inside the cylinder 2. During this rising, the secondary water exchanges heat with the primary water flowing inside the inverted U-shaped heat exchanger tube 3 and becomes high temperature.

On the other hand, since the pressure is approximately constant, the high temperature secondary water becomes below the saturation pressure and boils. As a result, a gas-liquid two-phase flow is generated within the inner cylinder 2. This gas-liquid two-phase flow continues to rise further and is separated into steam and liquid (water) in the separator 6. The dryness of the steam is increased in the dryer 7 and sent to the turbine from the steam outlet 11, and the liquid is transferred to the downcomer 12. It flows into the inner cylinder 2 again via .

FIG. 5 shows an enlarged view of the vicinity of the tube plate 4. As shown in this figure, the downward flow 30 of the secondary water that has descended through the downcomer 12 and the downward flow 30 that has descended between the legs of the inverted U-shaped heat exchanger tubes 3 are directed toward the upper part of the tube sheet 4. , and forms an upward flow 40 that rises between the inverted U-shaped heat exchanger tubes 3 .

In the conventional steam generator having the above configuration, the flow of secondary water above the tube plate 4 is reversed and the downward flow 3 is reversed as shown in FIG.
A stagnation portion 33 is created in the flow approximately at the center of the bundle of leg pieces of the inverted U-shaped heat exchanger tube 3 where the two converge and turn into an upward flow 40 . 3 in the diagram
2 shows streamlines of secondary water. In this stagnation part 33,
As shown in FIGS. 5, 7, and 8, a sludge accumulation portion 25 is formed. As shown in FIG. 8, this deposited portion 25 surrounds the inverted U-shaped heat exchanger tube 3 and is deposited on the tube plate 4, and its upper surface is covered with a solid-liquid mixed deposited layer 26.

This solid-liquid mixed sedimentary layer 26 moves up and down somewhat due to the flow of secondary water, but during this time C1- in the secondary water is concentrated and the reverse U
There was a possibility that local corrosion 35 would occur in the shape heat exchanger tube 3.

(Problems to be Solved by the Invention) Conventionally, in order to prevent the above-mentioned local corrosion of inverted U-shaped heat exchanger tubes, a large-scale device was used to remove sludge from the tube sheets during periodic inspections of JI subfurnaces. It took a lot of time to remove it. Although it is questionable whether removing sludge at each periodic inspection is appropriate in addition to preventing local corrosion of heat transfer tubes, it is important to measure the height of sludge that is accumulating during reactor operation. It is not possible to determine whether sludge should be removed even if the reactor is shut down.

Furthermore, as is clear from the above, local corrosion of heat exchanger tubes roughly corresponds to the sludge height position, so it is possible to diagnose the health of heat exchanger tubes and limit inspection points based on the height of accumulated sludge. However, it is currently not possible to measure the height of accumulated sludge during reactor operation.

The present invention has been made based on the above circumstances.

It is an object of the present invention to provide a method for measuring the height of sludge on a steam generator tube sheet, which is capable of measuring the height of sludge that is being accumulated during nuclear reactor operation.

(Means for Solving the Problems) The method for measuring the height of sludge on a steam generator tube sheet according to the present invention is to measure the temperature above a tube sheet that supports a large number of heat transfer tubes of a steam generator used in a pressurized water reactor. The temperature distribution profile is obtained by measuring the distribution at any time, and the sludge height on the tube sheet is determined from the sharp temperature gradient at the boundary between the sludge (solid phase) deposited on the tube sheet and the liquid phase that appears in this temperature distribution profile. It is characterized by

(Function) In the method for measuring the height of sludge on a steam generator tube plate of the present invention having the above configuration, at the boundary between the accumulated sludge and the liquid phase,
Since the height of the accumulated sludge is determined by utilizing the occurrence of a sharp temperature gradient in the temperature profile, the height of the sludge can be measured at any time even during operation of the nuclear reactor.

(Example) FIGS. 1A and 1B are diagrams showing temperature distribution profiles in the height direction from the tube sheet, which are the basis of the measurement method of the present invention. 1st
Figure A shows a case where there is no sludge deposited on the tubesheet, and it can be seen from this figure that when there is no sludge on the tubesheet, the temperature gradually decreases as the temperature moves upward from the tubesheet. FIG. 1B shows a case where sludge is deposited on the tube plate, and it can be seen from this figure that a sharp temperature gradient occurs at a position corresponding to the solid-liquid phase interface at the sludge height H. In these figures, 50 indicates the average temperature measurement value, 51 indicates the temperature fluctuation width, 52 indicates the temperature distribution profile, and 53 indicates the temperature gradient.

From the above phenomenon, the temperature distribution profile is constantly am
It can be seen that the height H of the accumulated sludge can be measured by detecting the appearance of the temperature gradient shown in FIG. 1B. Since the accuracy is determined by the interval between temperature measurement points, the interval can be made sufficiently fine as necessary, and since the temperature distribution can be measured at any time during the operation of the reactor, as a result, sludge accumulation can be prevented at any time. You can find the height.

When there is no sludge accumulation, the temperature distribution profile becomes a smooth curve as shown in FIG. 1A, so it is also possible to determine the presence or absence of sludge accumulation.

Furthermore, while the temperature measurement value in the liquid phase has a large fluctuation range 51 due to the flow of the liquid phase, the fluctuation range 51 in the sludge accumulation part (solid phase) is almost O. The boundary can correspond to the sludge accumulation height H.

Note that if the sludge height H is identified using both of the above, a more reliable value can be obtained.

The present invention utilizes this to make it possible to know the state of sludge accumulation on a tube sheet during operation of a nuclear reactor.

FIG. 2 is a schematic cross-sectional view of an embodiment of the measurement method of the present invention. In this figure, a rod-shaped temperature measuring device] 23 is installed on the tube sheet 4 in parallel with the heat transfer tubes, and this temperature measuring device is attached to the tube sheet 4.
A plurality of cylinders of temperature sensors 13a are attached at equal intervals in the axial direction further upward. Such a temperature measuring device 13
Since the temperature distribution profile above the tube plate 4 can be obtained, the sludge accumulation height H can be adjusted at any time according to the above explanation. Note that the temperature sensor 13
A typical example of a is a thermocouple. It is easy to lead the lead wire of such a temperature sensor out of the steam generator container in a fluid-tight manner, and measurement during operation is of course possible.

FIG. 3 is a schematic cross-sectional view of another embodiment of the invention. In this embodiment, a plurality of temperature sensors 13a are attached to the surface of the heat exchanger tube 3, distributed at equal intervals in the axial direction. In this embodiment as well, the sludge accumulation height H can be identified in the same manner as in the previous embodiment.

If a plurality of the above-mentioned temperature measuring devices are distributed and installed on the tube plate, the state of sludge accumulation can be grasped three-dimensionally.

[Effects of the Invention] As is clear from the above, in the steam generator of the present invention, the presence or absence of sludge accumulation on the tube sheet or its accumulation state can be known at any time during reactor operation. It is possible to estimate the possible locations of localized corrosion of the heat exchanger tubes, and it is possible to limit diagnosis and inspection points during inspections during the shared use period.

Therefore, the work required for diagnosis and testing can be simplified and shortened by one hour, and the reliability of testing is improved.

Furthermore, according to the measurement method of the present invention, it is possible to detect the occurrence of a situation in which it is determined that there is a large amount of sludge accumulation during the operation of a nuclear reactor, so that measures can be taken before a major problem occurs. As a result, the safety of the steam generator can be improved.

[Brief explanation of the drawing]

1A and 1B are diagrams for explaining the present invention in detail, FIG. 2 is a schematic cross-sectional view of one embodiment of the present invention, FIG. 3 is a schematic cross-sectional view of another embodiment, and FIG. Fig. 4 is a perspective view showing the entire conventional steam generator with two parts cut away, Fig. 5 is a longitudinal sectional view of the main parts of the conventional example, and Fig. 6 shows the flow of secondary water in the conventional example. FIG. 7 is a plan view of the main part, and FIG. 8 is a schematic cross-sectional view of the sludge accumulation section in the conventional example.

Claims (1)

[Claims] The temperature distribution above the tube sheet that supports the many heat transfer tubes of the steam generator used in pressurized water reactors is measured at any time to determine the temperature distribution profile, and the sludge ( A method for measuring the height of sludge on a steam generator tube sheet, which is characterized by determining the height of sludge on the tube sheet from the sharp temperature gradient at the boundary between the solid phase and the liquid phase.