JPH0727892A - Device for measuring water quauty environment at bottom of reactor pressure vessel - Google Patents

Abstract

PURPOSE:To directly measure the water quality environment at the reactor bottom by arranging water quality environment measuring device in the housing penetrating true bottom of reactor pressure vessel. CONSTITUTION:A water quality environment measuring equipment 21 is inserted in the reactor bottom position (a-part) in an in-core monitor housing 26 penetrating through the reactor bottom plate 25 of a reactor pressure vessel 10. At the reactor bottom, welded part (c-part) which is especially important for water quality environment (corrosion electric potential, solved oxigen, crack propagation velocity, etc.) exists between the lower plate 25 and the housing 26, and welding thermal effect part 27 exists in the housing 26 side. Inside the housing on the other hand, a gap part (b-part) exists between the housing 26 and the cover tube 28 of a local power region system detector (LPRM). A measuring equipment 21 measures the water quality of the reactor water flowing down the b-part and into the tube 28 and reaching the a-part and transmits the signal to the processing device with measured signal transmission cables 22 led out of the vessel 10 and then penetrating the containment. By this, water quality in the reactor bottom can be directly measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor bottom water quality measuring device for a reactor pressure vessel for grasping the water quality of a primary coolant in a boiling water reactor (hereinafter referred to as BWR).

[0002]

2. Description of the Related Art In a nuclear power plant, high-temperature high-pressure water is used as a reactor coolant, and under severe environmental conditions, the corrosion behavior of structural materials is an important issue. Particularly in BWRs, there is an example in which a phenomenon of stress corrosion cracking (hereinafter referred to as SCC. SCC is an abbreviation of Stress Corrosion Cracking) occurs in a heat-affected zone such as a welded portion in austenitic stainless steel piping.

It is generally said that this SCC phenomenon occurs when three factors, that is, materials, stress and environment, are superposed. SU as a material factor
The condition is a welded part of S304 type stainless steel. That is, there is a problem in that a chromium deficient layer is generated due to the precipitation of chromium carbide due to the heat effect during welding, and the yield strength is reduced. Further, as a factor of the stress, the residual thermal stress to the member that occurs during welding is also mentioned, and the residual stress is removed by improving the welding method or the like. On the other hand, environmental factors include impurities such as chlorine ions, dissolved oxygen, and the like existing in a corrosive environment of high-temperature water. Water quality of reactor coolants is strictly controlled in nuclear power plants, and efforts are made to keep primary water as neutral pure water as much as possible in BWR plants. Therefore, the impurity concentration is kept low. On the other hand, regarding the dissolved oxygen concentration, it is unavoidable that dissolved oxygen of about 200 to 300 ppb exists because oxygen is generated by radiolysis of water in the core. Therefore, as an environmental factor for SCC, the presence of dissolved oxygen is more important as well as the presence of impurity ions. At the reactor temperature (285 ° C), dissolved oxygen around 200 ppb is at a sufficient level to generate SCC.

Further, in recent years, in order to maintain material integrity and prolong the life of the reactor pressure vessel pressure boundary such as the reactor internals or the reactor bottom, which are in a more severe corrosive environment than the external core piping, Understanding the corrosive environment is an important issue. B by computer simulation
According to the model analysis of the water quality of the primary system of the WR plant, the dissolved oxygen concentration in the core is about 500 ppb to 800 ppb and even at the bottom of the reactor,
It has been shown to be about 0 ppb to 300 ppb.
It is said that hydrogen peroxide, which is expected to have corrosiveness equal to or higher than that of oxygen, exists in the range of several hundreds of ppb.

As described above, since the inside of the furnace is in a high radiation field, highly decomposing radiation decomposition products are present in a high concentration, and it is considered that the corrosive environment of the material is extremely severe.
Conventionally, the water quality of reactor water in the primary system of a BWR plant is measured by sampling the reactor water from a sampling point provided in a reactor re-environment system or a reactor coolant purification system, cooling it to room temperature, and then measuring it. This state is shown in FIG. That is, FIG. 7 is a system diagram showing the configuration of the BWR primary system hydrogen injection system. The steam generated in the core 1 works in the high-pressure turbine 2 and the low-pressure turbine 3 and is then guided to the condenser 4, where it is cooled and condensed to return to water. This condensate is heated and pressurized by a high-pressure condensate pump 7, a feedwater heater 8 and a feedwater pump 9 through a condensate pump 5 and a condensate purification system 6, and a reactor pressure vessel 10
Is injected into. On the other hand, the reactor water is the reactor recirculation pump 11
A part or all of them are forcedly recirculated outside the reactor, and a reactor cooling and purification system 13 is provided branching from the reactor recirculation system 12. Normally, the reactor water is sampled from either of these systems via the sampling line 14, and the dissolved oxygen concentration, conductivity, etc. are measured in the analysis rack 15.

[0006]

However, in the conventional water quality measurement of reactor water, as shown in FIG. 7, the reactor water is guided from the sampling point provided in the out-core pipe,
The water quality in the core 1 is not necessarily measured directly. Then, as already shown in the computer simulation result, it is expected that the water quality of the core 1 part and the water quality in the pipe outside the core will be significantly different. That is,
Due to the behavior of hydrogen peroxide, which is thermally unstable at high temperature, and the effect of recombination of oxygen and hydrogen in a part of downcomer, it is considered that there is a large difference in water quality between the core and the outside.

Therefore, in the conventional water quality measurement of reactor water, there was a problem that the in-reactor corrosive environment where the in-reactor structures are located cannot be accurately evaluated. In particular, maintaining the material integrity of the reactor pressure vessel pressure boundary such as the bottom of the reactor is extremely important for improving the plant operating rate and extending the life of the plant. However, no attempt has been made so far to directly grasp the water quality environment at the bottom of the reactor.

The present invention has been made in consideration of the above points, and it is possible to directly measure the water quality environment (corrosion potential, dissolved oxygen, crack growth rate, etc.) at the bottom of the reactor. It is intended to provide an environment measuring device.

[0009]

In order to achieve the above object, in the present invention, a water quality environment measuring instrument arranged in a housing penetrating the bottom of a reactor pressure vessel, and measurement from the water quality environment measuring instrument Measuring the water quality of the reactor bottom Vessel, which comprises a measurement signal transmission cable for transmitting a signal and penetrating the bottom of the hound, and a measurement signal processing device connected to the other end of the measurement signal transmission cable. Provide a device.

[0010]

With this configuration, the water quality environment measuring instrument is arranged in the housing and is located at the height of the reactor bottom of the reactor pressure vessel. A local power range detector (hereinafter referred to as LPRM) and the like are inserted in this housing. Since cooling holes are formed in this LPRM, the reactor water flows axially upward in the housing. It is in circulation. Therefore, it is possible to directly measure the water quality at the bottom of the furnace by the water environment measuring instrument arranged in the housing.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a reactor bottom water quality environment measuring apparatus according to the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a system diagram showing a BWR primary system configuration. The steam generated in the core 1 works in the high-pressure turbine 2 and the low-pressure turbine 3, and then is guided to the condenser 4, where it is cooled and condensed to return to water. The condensate is heated and pressurized by a high-pressure condensate pump 7, a feed water heater 8 and a feed water pump 9 via a condensate pump 5 and a condensate purification system 6, and is injected into a reactor pressure vessel 10. On the other hand, a part or all of the reactor water is forcibly recirculated outside the reactor by a reactor recirculation pump 11, and a reactor cooling and purification system 13 is provided by branching from this reactor recirculation system 12. There is.

In this embodiment, the water environment measuring instrument 21
Is inserted at the position of the bottom of the in-core monitor housing 26 which is a housing penetrating the bottom bottom mirror 25 of the reactor pressure vessel 10. Measurement signal from this water quality environment measuring instrument 21
A cable 22 for transmitting a measurement signal is connected to the water environment measuring instrument 21 for transmitting the signal 21a. The measurement signal transmission cable 22 penetrates the bottom of the in-core monitor housing 26, and after exiting the reactor pressure vessel 10, further penetrates the containment vessel 23 and is installed outside the containment vessel 23. It is connected to the signal processing device 24.

Next, the operation of the first embodiment constructed as above will be described. FIG. 2 is a vertical cross-sectional view showing the furnace bottom portion in FIG. 1 in an enlarged manner. Particularly important parts of the water quality environment at the bottom of the furnace are parts b and c in the figure.
That is, there is a welding portion between the reactor bottom lower mirror 25 of the reactor pressure vessel 10 and the in-core monitor housing 26, and on the in-core housing 26 side, there is a welding heat-affected zone which causes a problem in material integrity.
There are 27. On the other hand, inside the in-core monitor housing 26, there is an LPRM cover tube 28 that constitutes an LPRM, and inside this LPRM cover tube 28, a mobile in-core instrumentation (hereinafter referred to as TIP) is inserted. A gap between the LPRM cover tube 28 and the in-core monitor housing 26 is a portion b in the figure. Therefore, if the water quality environment of the part b is bad, the material integrity is impaired from the inner surface of the in-core monitor housing 26, and if the water quality of the part c is bad, the material integrity is impaired and damage such as stress corrosion cracking occurs. Occurred, and eventually the reactor pressure vessel
It leads to a situation such as leakage of reactor water from 10.

In place of the in-core monitor housing 26, a control rod drive mechanism (hereinafter referred to as CRD) housing.
In the case of 31, as shown in FIG. 3, the furnace bottom end plate 25 and the stub tube 32, the stub tube 32 and the CRD housing
There are two welds 32a and 32b between 31.

The effect of the first embodiment will be described. The water quality environment measuring instrument 21 is installed in part a of FIG. The part a has the same temperature and the same radiation dose rate as the part b, and the reactor water descends the part b to the LPRM cover tube.
It enters the LPRM cover tube 28 via the cooling pores at the bottom of the 28 and forms an ascending flow to reach part a. Therefore, the water quality of part a is considered to be almost the same as that of part b.
In this way, by installing the water quality environment measuring instrument 21 in the portion a, the water quality in the portion b can be measured.

Next, a second embodiment will be described with reference to FIG. In FIG. 4, one or a plurality of pores 28a are formed at the position b of the LPRM cover tube 28 so that the reactor water in the part b directly flows into the part a and comes into contact with the water quality measuring instrument 21. There is.

The second embodiment has an advantage that the water quality environment of the part b can be measured more directly. Further, a third embodiment will be described with reference to FIG. In FIG. 5, the pores formed in the LPRM cover tube 28 in the second embodiment.
In addition to 28a, the in-core monitor housing 26 also has pores 26
One or several a's are formed so that the reactor water in the c-section directly flows into the a-section via the b-section and comes into contact with the water environment measuring instrument.

The third embodiment has an advantage that the water quality environment of the reactor water at the portion where the weld c directly contacts the reactor water can be directly measured. Examples of the type of the water quality environment measuring instrument 21 include a corrosion potential measuring instrument, a dissolved oxygen measuring instrument, a crack progress measuring instrument, and a dissolved hydrogen measuring instrument. Further, other measurement items include temperature, conductivity, pH, hydrogen peroxide and the like.

In the above embodiment, the LP of the LPRM detector
Although the RM cover tube 28 is used as a storage container for the water quality environment measuring instrument 21, a dedicated container may be provided as a storage container for the water quality environment measuring instrument 21.

That is, the LPRM detector to be inserted into the reactor pressure vessel 10 has recently come to have a preliminary hole (penetration) as its range becomes wider. It is also possible to provide a container having substantially the same shape as the conventional LPRM detector in this preliminary hole, and to install the water quality environment measuring instrument 21 housed in this container at the bottom position of the furnace.

Further, a fourth embodiment is shown in FIG. In this embodiment, in an actual plant, hydrogen injection is performed via the hydrogen injection device 31 in order to reduce the concentration of dissolved oxygen in the furnace. In order to control the hydrogen injection amount, the output signal 24a of the measurement signal processing device 24 is input to the hydrogen injection amount control device 32, and the hydrogen injection amount is controlled by the output signal 24b from the hydrogen injection amount control device 32. it can.

For example, when the hydrogen environment measuring instrument 21 is a corrosion potential measuring instrument, the hydrogen injection amount should be controlled so that the indicated value is -230 mV (SHE) or less, and the soundness of the material at the bottom of the furnace should be ensured. You can

[0023]

According to the present invention, it is possible to directly grasp the water quality at the bottom of the furnace, which could not be confirmed until now. As a result, it becomes possible to evaluate the material integrity of the pressure-resistant boundary part of the furnace bottom from the viewpoint of environmental factors, and it has an effect of contributing to the study of extending the life of the plant.

[Brief description of drawings]

FIG. 1 is a system diagram showing a first embodiment of a reactor pressure vessel bottom environment measuring device according to the present invention.

FIG. 2 is an enlarged vertical sectional view showing a furnace bottom portion of the reactor pressure vessel furnace bottom environment measuring apparatus shown in FIG.

FIG. 3 is a vertical cross-sectional view showing a welded portion in a furnace bottom portion of a control rod drive mechanism housing.

FIG. 4 is an enlarged vertical sectional view showing a reactor bottom of a second embodiment of the reactor pressure vessel furnace bottom environment measuring device according to the present invention.

FIG. 5 is an enlarged vertical sectional view showing a reactor bottom of a third embodiment of the reactor pressure vessel furnace bottom environment measuring device according to the present invention.

FIG. 6 is a system diagram showing the configuration of a fourth embodiment of the reactor pressure vessel bottom environment measuring apparatus according to the present invention.

FIG. 7 is a system diagram showing a configuration of a conventional water quality measuring device.

[Explanation of symbols]

 10 ... Reactor pressure vessel 21 ... Water environment measuring instrument 21a ... Measurement signal 22 ... Measurement signal transmission cable 24 ... Measurement signal processing device 25 ... Reactor bottom lower mirror 26 ... In-core monitor housing 27 ... Welding heat affected zone 28 ... LPRM cover tube

Claims (5)

[Claims] 1. A water environment measuring instrument arranged in a housing penetrating the bottom of a reactor pressure vessel, and a measurement signal transmitting cable for transmitting a measurement signal from the water quality measuring instrument and penetrating the bottom of the housing. And a measurement signal processing device connected to the other end of this measurement signal transmission cable, a reactor pressure vessel bottom water quality environment measuring device. 2. The reactor bottom water quality environment measuring device according to claim 1, wherein a corrosion potential measuring device is arranged as the water quality environment measuring device. 3. The reactor bottom water quality environment measuring apparatus according to claim 1, wherein a dissolved oxygen meter is arranged as the water quality environment measuring instrument. 4. The reactor bottom water quality environment measuring apparatus according to claim 1, further comprising a crack growth meter as the water quality measuring instrument. 5. The reactor bottom water quality environment measuring device according to claim 1, wherein a dissolved hydrogen meter for measuring hydrogen in the reactor water is arranged as the water quality environment measuring device.