JPH02159599A - Determination of leakage source in nuclear reactor containment - Google Patents

Abstract

PURPOSE:To determine a leakage source by measuring concentrations and the constitution of radioactive nuclides in an atmosphere in a nuclear reactor containment and by comparing the measured results with a concentration ratio of radioactive nuclides in a nuclear reactor water and a main steam. CONSTITUTION:A nuclear reactor pressure vessel 2 is contained in a nuclear reactor containment 1. A radioactive nuclides analyzer 21 which samples an atomospheric gas in the containment 1 and analyzes concentrations and a constitution of radioactive nuclides in the gas, and a judgement device 22 of a leakage source based on an analyzed results of the analyzer 21, are installed. In case that a leakage in a nuclear reactor primary system occurs in the containment 1, a leaking water vaporizes in the containment 1 to raise a dew point temperature and to be dried up by a drier 14 as well, flows into a sump tank 18 through a drain pipe 16 and then is discharged to outside the containment 1 through a sump water transfer pipe 20. Radioactive nuclides contained in the leaking water are discharged to an atmosphere in the containment 1, attenuates by their decaying or stick to various kinds of equipments and pipings, or move into a condensed drain water in the drier 14. The leakage sources are consequently determined by the devices 21 and 22.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention provides a method for detecting whether leakage occurs from the primary system in the reactor containment vessel, whether the source of the leak is the reactor water system or the main steam. The present invention relates to a method for determining whether the system is a system.

(Prior art) In boiling water nuclear power plants, if reactor water or main steam leaks from the primary system including the reactor pressure vessel within the reactor containment vessel and the amount of leakage exceeds the allowable amount, In order to ensure the safety of the plant, it is necessary to stop plant operation, find the source of the leak early, and take necessary measures to prevent the leak. Conventionally, methods for determining whether the leak source is from the reactor water system or the main steam system include determining the leak source by measuring the hydrogen concentration in the atmospheric gas in the reactor containment vessel, or by determining the leak source from the reactor water system or the main steam system. There are methods to determine the leak source by detecting radionuclides in leaked water flowing into a sump tank in the reactor containment vessel.

However, the former method has a problem in that it takes time to obtain a determination result because the leak source is determined from changes in hydrogen concentration over time. In addition, the latter method has the problem that accurate determination results cannot be obtained because the radionuclides decay and the concentration decreases while the leaked water flows into the sump tank.

(Problems to be Solved by the Invention) As mentioned above, in the past, the source of the leak was determined from the hydrogen concentration in the atmospheric gas in the reactor containment vessel and the radionuclides in the leaked water, so it took a long time to obtain the determination result. Moreover, it was not possible to obtain accurate judgment results.

The purpose of the present invention has been made in view of the above-mentioned problems, and when a leak of reactor water or main steam occurs in the reactor containment vessel, whether the leak source is the reactor water system or the main steam is detected. It is an object of the present invention to provide a method for determining a leak source in a reactor containment vessel, which can quickly and accurately determine whether the reactor is a steam system.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention measures the concentration and composition of radionuclides in the atmosphere inside the reactor containment vessel, and transmits the measurement results to the reactor. This method is characterized by comparing the concentration ratio of radionuclides in reactor water and live steam to determine the source of leakage in the reactor primary system.

(Function) In the present invention, by determining the concentration and composition of radionuclides in the atmosphere inside the reactor containment vessel, it is possible to know the concentration ratio of radionuclides in the atmosphere inside the reactor containment vessel. can. Therefore, by comparing the concentration ratio of radionuclides in the atmosphere inside the reactor containment vessel with the concentration ratio of radionuclides in reactor water and main steam, we can compare the concentration ratio of radionuclides in reactor water and the main steam. Since this is numerically significantly different from the concentration ratio of radionuclides in steam, it is possible to quickly and accurately determine whether the leak source is the reactor water system or the main steam system.

(Example) FIG. 1 is a diagram showing a schematic configuration of a boiling water type atomic couplant to which the method of the present invention is applied, in which a reactor pressure vessel 2 is housed in a reactor containment vessel 1.

A reactor water supply pipe 3 and a main steam pipe 4 are connected to the reactor pressure vessel 2, and the reactor water supplied from the reactor water supply pipe 3 into the reactor pressure vessel 2 is transferred to the reactor recirculation pipe 5. After being circulated and agitated by the provided reactor recirculation pump 6, it flows into the reactor core (not shown) housed in the reactor pressure vessel 2 from below. The reactor water that has flowed into the reactor core is heated by the nuclear reaction heat of the reactor core, becomes high-temperature, high-pressure steam, flows out from the main steam pipe 4, and is sent to a turbine power generation system (not shown). In addition, reactor pressure vessel 2
A control rod drive mechanism 7 is provided at the bottom of the control rod drive mechanism 7, and the control rod drive mechanism 7 drives a control rod (not shown) up and down. Note that a drive water pipe 8 is connected to the control rod drive mechanism 7.

Atmospheric gas within the reactor containment vessel 1 is sucked into a sampling pipe 10 by a sample pump 9. This sampling pipe 10 is provided with a dew point hygrometer 11, a hydrogen concentration meter 12, and a radiation monitor 13, and these detectors measure the dew point temperature, hydrogen concentration, and radiation dose inside the reactor containment vessel 1. It has become. In addition, the atmospheric gas inside the reactor containment vessel 1 is constantly dehumidified by the cooling water flowing through the cooling water pipe 15 of the dehumidifier 14.
The condensed drain water generated in step 4 passes through the drain pipe 16, passes through the drain flow meter 17, and flows into the sump tank 18. The condensed drain water that has flowed into the sump tank 18 is pressurized by the transfer pump 19 and is discharged to the outside of the reactor containment vessel 1 through the sump water transfer piping 20.

In addition, 21 in the figure samples the atmospheric gas inside the reactor containment vessel 1 to detect radioactive nuclides (for example, N-13°F (8,
r-1: a radionuclide analyzer for analyzing the concentration and composition of H, l-133, etc.; 21 is the radionuclide analyzer 21;
This is a leak source determination device that determines the leak source based on the analysis results.

In the above configuration, when a leak occurs in the primary reactor system within the reactor containment vessel 1, the leaked water evaporates within the reactor containment vessel 1, increases the dew point temperature, and is dehumidified by the dehumidifier 14. Drain piping 16 and drain flow meter 17
After flowing into the sump tank 18 through the transfer pump 19
through the sump water transfer piping 20 to the reactor containment vessel 1.
Expelled outside. On the other hand, various radionuclides contained in the leaked water are released into the atmosphere inside the reactor containment vessel 1, and decay and attenuate according to their respective half-lives. may adhere to equipment, piping, etc., or may migrate into the condensed drain water of the dehumidifier 14. The mass balance of radionuclides in the atmosphere within the reactor containment vessel 1 when leakage occurs from the primary system within the reactor containment vessel 1 is expressed by the following equation.

Ru.

Furthermore, by transforming the equation (2), the equation (3) for determining the leakage rate of leaked water in the reactor containment vessel 1 can be obtained.

C1: Concentration of radionuclide i in the containment vessel atmosphere (μCl
/ rri+) CL: Concentration of radionuclide i in leaked water (μc+/g) L: Leakage rate (g/Hr) V: Internal volume of containment vessel (rn') λ,: Radionuclide decay constant (H+'') α , :Adhesion coefficient of radionuclide in the containment vessel (rr?/1lr) Here, when the concentration C1 of the radionuclide i in the atmosphere in the reactor containment vessel 1 is in an equilibrium state, dc+ /
Since d t-0, if the equilibrium concentration of radionuclide i in the atmosphere inside the reactor containment vessel 1 is expressed as C0, then equation (2) is obtained from equation (1), where: The concentration ratio of the two types of radionuclides 12j is expressed by the following equation.

RL: Nuclide concentration ratio in leaked water inside the containment vessel C, ,: Nuclide j
Equilibrium concentration of the atmosphere in the containment vessel (μC1/resistance) λ,: Nuclide myolysis constant (Hr) α,: Adhesion coefficient of nuclide in the containment vessel (rd/Hr) CL: Concentration of nuclide jk in leaked water (μC+/ g) RA: Nuclide concentration ratio in the atmosphere inside the containment vessel. Here, if the adhesion coefficients of two types of radionuclides are the same, C1- in equation (4)
By setting α), equation (5) for determining the adhesion coefficient can be obtained.

Furthermore, by substituting equation (5) into equation (3), equation (6) is obtained which calculates the leakage rate from the concentration ratio when the adhesion coefficients of two types of radionuclides i and j are the same.

Therefore, in the present invention, by measuring the concentration of radionuclides released in the reactor containment vessel 1 and comparing it with the concentration ratio of radionuclides present in the reactor water and main steam, it is possible to determine whether the leak source is an atom. It can be determined whether it is the reactor water system or the main steam system. For example, N-13 in the reactor containment vessel 1,
The relationship between F-18 and N-13 and F-18 in the leaked water is (
7) It is expressed by the formula.

CL: N-13 radioactivity concentration in leaked water (μC+/g) λN-13: N-13 decay constant (4,175Hr-'
) αN-l3: Adhesion coefficient of N-13 inside the containment vessel (r
d/)lr) C,,: Concentration of N-13 in the containment vessel (μC, /i) V: Containment vessel body fa (m') CL: F-18 radioactivity concentration in leaked water (μc, /g
) λp-+s: P-18 decay constant (0,379Hr
-') αp-+s: Adhesion coefficient of F-18 in the containment vessel (rr?/Hr) C-*: Concentration of F-18 in the containment vessel (μC1/rr
1') Here, in equation (7), the adhesion coefficient in the reactor containment vessel 1 can be ignored due to the chemical properties of N-13 and F-18, so equation (8) is obtained from equation (7).

By using equation (8), the concentration ratio of N-13 and F-18 in the leaked water is determined from the concentration ratio of N-13 and F-18 in the atmosphere inside the reactor containment vessel 1, and the The leak source is determined using the fact that the N-13/F-18 concentration ratio in water is about 25/1 and the N-13/F-18 concentration ratio in main steam is about 4/1. Furthermore, by using equation (3), it is possible to evaluate the leakage rate.

Figure 2 shows the concentration ratio of radionuclides released into the reactor containment vessel 1 when a leak occurs from the primary system within the reactor containment vessel 1, and both N-13 and F-18 are 5
Since only gamma rays of about 11 KeV are emitted, the measurement is based on the gamma rays of a sample taken from the atmospheric gas inside the reactor containment vessel 1.
The line peak intensity is continuously measured and a sample attenuation curve as shown in FIG. 2 is created. The decay curve of the sample is N
-13's attenuation curve aaF-18's attenuation curve is a composite curve, and its shape depends on the concentration ratio of N-13 and F-18. Here, N-13/ in the reactor water
Since the F-111 concentration ratio is about 25/1 and F-18 is small, the attenuation curve of the sample will be as shown by curve C when the leak source is the reactor water system. In addition, if the leak source is the main steam system, N-13/F-18 in the main steam
Since the concentration ratio is about 4/1 and F-18 is large, the attenuation curve of the sample is as shown in d.

Therefore, N-1 in the atmosphere inside the reactor containment vessel 1
By measuring the concentration ratio of F-3 and F-18 and finding the attenuation curve, it is possible to determine whether the leak source is the reactor water system or the main steam system.

Note that the present invention is not limited to the above embodiments.

For example, in the above embodiment, the concentration ratio of N-13 and F-18 in the atmosphere inside the reactor containment vessel 1 was determined as a1, but the concentration ratio of l-131 and l-133 was measured, and the The results are summarized as I-131/ in the reactor water and main steam.
The leak source may be determined by comparing with the l-133 concentration ratio.

To explain specifically, I in the reactor containment vessel 1
The behavior of I-131 and 1-113 is considered to be the same, and the sticking coefficient in the reactor containment vessel 1 is considered to be the same. Therefore, the relationship between the concentration ratio of I-131 and l-133 and the leakage rate is expressed by the following equation. shown.

L: Leak rate (g/1lr) RL: l-1317I-133 concentration ratio in leaked water (-
) RA: 1-1317 in the atmosphere inside the containment vessel! -133
Concentration ratio (-) ■ = Containment vessel internal volume (rr?) λr-+*,: l-131 decay constant (3,591x 1O-3Hr-') cL: Concentration of l-131 in leaked water (μC+ /g ) C□: Concentration of l-131 in the containment vessel atmosphere (u
C+/rn') λI-+33: l-133 decay constant (3,316X
1O-211r-RL-: l-133/l-131 concentration ratio in leaked water (-
) RA: l-1337I-131 in the containment vessel atmosphere
Concentration ratio (-) CL: Concentration of l-133 in leaked water (μC+
/g) Summer-133 C,,: Concentration in the atmosphere inside the containment vessel of J-133 (u
C+ / rrI') Using the above equations (9) and (10), determine the leak source inside the reactor containment vessel 1 from the concentration ratio of I-131 and l-133 in the atmosphere inside the reactor containment vessel 1. Evaluate the assumed leakage rate assuming that it is reactor water or main steam. The leak source can be determined by comparing this leak rate evaluation with the leak rate determined from the sump water discharge amount in the reactor containment vessel or the indicated value of the drain flow rate system.

[Effects of the Invention] As described above, according to the present invention, the concentration and composition of radionuclides in the atmosphere inside the reactor containment vessel are determined, and the measurement results are used to determine the radioactivity in the reactor water and main steam. Since the leak source is determined by comparing the nuclide concentration ratio, it is possible to accurately and quickly determine whether the leak source is the reactor water system or the main steam system. Therefore, early detection of secondary system leakage sources and countermeasures when the plant is shut down become extremely easy, which can greatly contribute to improving the safety and reliability of boiling water nuclear power plants.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams for explaining the method of determining leakage sources in the reactor containment vessel according to the present invention, in which Figure 1 is a schematic configuration diagram of a boiling water type nuclear couplant, and Figure 2 is a diagram of the reactor containment vessel. FIG. 3 is a diagram showing a decay curve of radionuclides released within the lumen. 1... Reactor containment vessel, 2... Reactor pressure vessel, 3
...Reactor water supply piping, 4...Main steam piping, 5...
Reactor recirculation piping, 6...Reactor recirculation pump, 7.
... Control rod drive mechanism, 8... Drive water piping, 9... Sampling pump, 10... Sampling piping, 14
...Dehumidifier, 16...Drain flow meter, 21...Radioactive nuclide analyzer, 2...Leak source determination device.

Claims (1)

[Claims] Measures the concentration and composition of radionuclides in the atmosphere inside the reactor containment vessel, and compares the measurement results with the radionuclide concentration ratio in the reactor water and main steam to determine the source of leakage in the reactor primary system. A method for determining a leak source in a reactor containment vessel, characterized by: