JPS59150388A - Method of judging leakage source in reactor container - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides a method for determining whether the leak source is a steam system or a cooling water system when a leakage accident occurs in the containment vessel of a boiling water nuclear power plant. This invention relates to a method for accurately determining a leak source in a reactor containment vessel.

[Technical Background of the Invention] In a boiling water nuclear power plant, if a leakage accident occurs in the containment vessel and the amount of leakage exceeds a certain value, plant operation must be stopped to ensure plant safety. It is necessary to stop the operation, search for the source of the leak, and take necessary measures.

If a leak occurs from the primary system inside the reactor containment vessel, the first thing to do is to increase the dew point temperature due to a rise in the temperature inside the containment vessel, increase the flow rate of condensed water drain in the dehumidification system inside the containment vessel, or Based on the change in the radiation monitor instruction (8), leakage from the -order system into the containment vessel can be detected.

In addition, if radionuclides are detected by measuring the radioactivity of the atmospheric gas inside the containment vessel or the radioactivity of the sump water flowing into the containment vessel dehumidifying system condensed water drain, the reactor water,
It is possible to detect leaks from the steam system.

[Problems with the background technology] However, in the past, there was no quantitative determination of whether the leak source was reactor water or steam, or a quantitative evaluation of the amount of leakage. This has the disadvantage of making it difficult to investigate the source of the leak after the plant has been shut down due to a primary system leak occurring within the container, and countermeasures being delayed.

Figure 1 shows changes in hydrogen concentration in the containment vessel, dew point temperature, radiation monitor instructions, and leakage amount when a leak occurs from the negative system within the reactor containment vessel.
.

In the figure, when leakage occurs from the primary system in the containment vessel at point K, the amount of leakage increases as shown by curve A with time.

In addition, 1. Since radioactive materials are brought into the containment vessel due to the primary system leakage, the indication of the containment vessel radiation monitor also rises as shown by curve B.

On the -° side, the dew point temperature indication inside the containment vessel changes in a curved manner due to the primary coolant leaking into the containment vessel.

By the way, when the water in the reactor coolant undergoes radiolysis by neutrons, the amount of C in the reactor water changes from 20 to 2 in 2 days.
Hydrogen gas is produced by reactions such as H2+02. A portion of this generated hydrogen gas will migrate into the main steam, and a portion will be dissolved in the reactor water.

In this case, the hydrogen concentration of main steam and reactor water is 0°C, 1
In a volume ventilation nostril under standard conditions of atmospheric pressure, this results in approximately 30 CIll/distillation of steam, and 0.22 cni'/kg of water.

From this, if main steam or reactor water in the secondary system leaks into the containment vessel, the concentration of hydrogen, which is a non-condensable gas, will be
It increases with time and changes like straight lines C1 and C2 in FIG. Therefore, when the leakage amounts of reactor water and main steam are the same, the hydrogen concentration change C1 due to steam leakage is approximately 170 times the hydrogen concentration increase characteristic C2 due to reactor water leakage.

In addition, among the radionuclides present in the Ryoko reactor water, iodine nuclides such as I-1, 31 and I-''1.35 migrate into the main steam at a concentration of about 2 x 10-2 of the reactor water. Na-24
, Mn-56, etc., it is empirically known that approximately 1o-→ of radioactive nuclides such as Mn-56 is transferred to the main steam.

Therefore, for example, the radioactive concentrations of l-131 and Na-24 in the reactor water are Aμc/n+J2 and BμC/II, respectively.
At 1°C, r-131i1 in the main steam! Degree and Na-
21! Degree is 2X10-2XAμ0/IIIJ2 respectively
．． 1'0-4xs, czc /Ill J2.

Here, the number l-131 in the reactor water or main steam is
Let the concentration ratios of and Na-24 be RW and R8, respectively.

Rw = FM degree (1-131)/IIR (Na -24
)=A/B...(1) Rs=2x10-2xA/(10-'xB)=, 20O
A/B...(2).

As is clear from these formulas, l-131 and Na-2
The m degree ratio of 4 is 200 times higher than that of the main steam in the reactor water.

If a leak occurs from the secondary system in the containment vessel, the hydrogen gas concentration in the containment vessel will increase as described above, and the liters contained in the leaked primary cooling water will increase.
Since radionuclides such as -131 and Na-24 will be detected in the containment vessel, the above-mentioned significant difference in the radioactivity concentration ratio can be used to determine whether the leak source is the steam system or the cooling system. It is possible to accurately determine whether

[Objective of the Invention] The present invention was made based on the above-mentioned knowledge, and is based on the hydrogen gas concentration, radionuclide composition ratio, and radioactivity concentration ratio, which are significantly different between reactor water and steam. The objective is to obtain a method for determining the source of leakage from the primary system into the containment vessel by measuring hydrogen gas in the reactor containment vessel atmosphere, or by measuring the radionuclide composition and concentration in the containment vessel atmosphere and sump water. That is.

[Summary of the Invention] The method of determining a leak source in a reactor containment vessel according to the present invention is based on hydrogen gas concentration and radionuclide radioactivity concentration in the atmosphere within the reactor containment vessel, and radionuclide radioactivity in sump water within the containment vessel. This method measures the concentration and determines whether the leak source is from the steam system or the reactor water system based on these measurement results.

[Embodiments of the invention] The details of the present invention will be explained below with reference to FIG.

Fig. 2 schematically shows the system piping of the reactor containment vessel to which the method of the present invention is applied. The reactor water is circulated and agitated by the reactor recirculation pump 6 provided in the reactor recirculation piping 5. Drive water is supplied to the reactor control rod drive mechanism 7 through a drive water pipe 8 for the reactor control rods. The atmosphere inside the containment vessel 1 is sucked into the containment vessel sampling piping 10 by a containment vessel atmosphere sample pump 9, and a dew point hygrometer 11 and a hydrogen concentration meter 12 are used.
, the dew point humidity, hydrogen concentration, and radioactivity are measured by the radioactivity monitor 13.

The atmosphere inside the containment vessel is also maintained by a constant dehumidifier 14.
It is cooled and dehumidified by the cooling water introduced from the cooling water pipe 15. The dehumidified condensed water drain passes through the dehumidifier drain piping 16, and after its flow rate is monitored by the drain flow meter 17, it flows into the sump 18 in the containment vessel, is further pressurized by the sump discharge pump 19, and then flows into the discharge piping 20. After that, it is discharged outside the containment vessel 1.

If a leak occurs in the primary system within the reactor containment vessel configured as described above, the leaked coolant will evaporate within the containment vessel, increasing the dew point temperature and causing the containment vessel dehumidifier 14 to evaporate.
After being dehumidified by and flowing into the containment vessel sun 718,
It is discharged outside the containment vessel 1. On the other hand, since the hydrogen gas contained in the leaked secondary coolant is non-condensable, it accumulates and increases in the containment vessel.

In the present invention, the primary coolant leakage is determined using the following equation based on the change in the indication of the hydrogen concentration meter 12 in the containment vessel, the amount of water discharged from the sun 118 in the containment vessel, or the indication of the containment vessel dehumidifier drain flow meter 16. Determine the source and assess the adequacy of the leak amount if necessary.

That is, when the primary coolant leaks from the steam system represented by the main steam pipe 4, the hydrogen concentration in the containment vessel 1 is expressed by the following equation. , X=30XLXT/V...(3) However, X:
Hydrogen in the containment vessel 1 hour after the leak occurred (p
pm) L: Primary system coolant leakage rate from the main steam system (kg/hr,) ■ = Containment vessel volume (T113) T: Elapsed time after secondary system leakage (hr,) Similarly, reactor recirculation In the case of reactor water leakage from the reactor-subsystem piping represented by the piping 5, etc., the hydrogen concentration in the containment vessel 1 is expressed by the following equation.

Y-0,・22XLXT/V... (4) However, Y: Hydrogen concentration in the containment vessel 1 hour after the leakage occurrence (ppm) As is clear from equations (3) and (4) In the case of a leak from the main steam system, the hydrogen concentration in the containment vessel will be about 170 times higher than that in a reactor water leak for the same amount of leakage, and there will be significant differences depending on the leak source. The source of the leak can be determined by comparing it with the amount of water discharged from the sump, etc.

In addition, if main steam or reactor water leaks into the containment vessel,
Most of the leaked reactor water evaporates inside the containment vessel, and dehumidifier 1
4, and flows into the containment vessel sump 18 via the dehumidifier drain pipe 16, and a portion directly flows into the containment vessel sump 18.
flows into. As a result, radionuclides contained in the primary coolant leaking into the containment vessel eventually flow into the containment vessel sump 18.

Therefore, the radionuclide 1-13 in the containment vessel sump water
1.Measure Na-24, etc., and calculate the concentration ratio, R=(I-1
31), /<Na −24). When this m degree ratio R is equal to the concentration ratio of ■-131 and Na-24 in the reactor water, the primary coolant leaking into the containment vessel is the reactor water itself.

In addition, the concentration ratio R is higher than the concentration ratio of reactor water, and is 100 (
When it is around 8, it is determined that there is a leak from the steam system, such as the main steam. This means that the transfer rate of iodine to the vapor phase such as main steam is Na
This is because it is about 200 times higher than -24 mag.

[Effects of the Invention] As described above, according to the present invention, the hydrogen concentration in the atmosphere inside the containment vessel is measured, and the amount of water drained from the condensed water drain from the dehumidification system inside the containment vessel or the water discharged from the sump inside the containment vessel is comparatively evaluated. By performing this, it is possible to estimate the source of the primary leak within the containment vessel, and it is also possible to estimate the amount of leakage.

In addition, by determining and evaluating the concentration ratio of l-131 and Na-24, which will be present in the containment vessel sump water due to secondary system leakage, it is possible to determine the source of the primary system leak inside the containment vessel. It becomes possible. As a result, it is extremely easy to quickly identify secondary leakage sources and take appropriate action when the blunt is stopped.
This can greatly contribute to ensuring and improving the safety of boiling water atomic power plants.

Note that leakage into the containment vessel is not limited to main steam and reactor water, but can also include water that contains almost no radioactivity, such as dehumidifier cooling water, reactor feed water, and control rod drive water.
According to the method described in the present invention, it is possible to roughly classify leak sources based on the presence or absence of radioactivity and the presence or absence of an increase in hydrogen concentration.

Also, the concentration of various nuclides and oxygen (02) present in main steam and reactor water? It is also possible to evaluate the source of leakage and the amount of leakage by focusing on 11 degrees or the like and using the same method as above.

[Brief explanation of drawings]

Figure 1 is a graph illustrating the atmospheric dew point temperature, hydrogen concentration, radiation monitor instructions, and changes in leakage amount in the containment vessel when leakage occurs from the primary system in the containment vessel, and Figure 2 is a graph showing boiling water. FIG. 2 is an explanatory diagram showing an overview of the inside of a reactor containment vessel of a nuclear power plant. 1... Reactor containment vessel 2...
・・・・・・・・・Nuclear dormitory 3・・・・・・・・・Reactor water supply piping 4・・・・・・
・・・・・・・・・Main steam piping 5・・・・・・・・・・・・
・Reactor recirculation piping 6...Reactor recirculation pump 7...Reactor control rod drive curve 8... ...... Drive water piping 9...
・・・・・・・・・Containment vessel atmosphere sample pump 1
0...... Containment vessel sampling piping 11... Dew point hygrometer 12...
......Hydrogen concentration meter 13...
...Radioactivity monitor 14...Dehumidifier 15...Cooling water piping 16...
......Dehumidifier drain piping 17...
・・・・・・Drain flow meter 18・・・・・・・・・・・・
Sump in the containment vessel 19...Sump discharge pump 20...Discharge piping agent Patent attorney Sa Suyama -

Claims (2)

[Claims] (1) Measure the hydrogen gas concentration and radionuclide radioactivity concentration in the atmosphere inside the reactor containment vessel, as well as the radionuclide radioactivity concentration in the sump water inside the containment vessel, and based on these measurement results, determine whether the leak source is steam. 1. A method for determining a leak source in a reactor containment vessel, the method comprising determining whether the leak source is a nuclear reactor water system or a reactor water system. (2) 1-131 and Na-24 are used as radionuclides, and the leak source is determined based on the radioactivity concentration ratio in the atmosphere and in the sump water. Method for determining the source of leakage in the reactor containment vessel described.