JPS60256100A - Method of decontaminating nuclear reactor system piping - 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 relates to a method for decontaminating nuclear reactor system piping in a boiling water nuclear power plant (hereinafter abbreviated as BWR).

[Technical Background of the Invention] Normally, in a BWR plant, pure water is used as primary cooling water and steam is generated in a reactor pressure vessel. In this reactor pressure vessel (1) Metal impurities in the reactor water are activated by neutron irradiation and radioactive metal ions "C02+, 54
M 01+ etc. are generated. The radioactive metal ions flow through a reactor water recirculation line connected to the reactor pressure vessel.

Therefore, the inner surface of the reactor recirculation line has C02+, 'M
Radioactivity such as n'+ is attached.

The BWR plant has a nuclear reactor system as shown in the attached diagram.

That is, a reactor core 2 is disposed in a medium heat section within a reactor pressure vessel 1, and a jet pump 3 is disposed on a side surface of this reactor core 2. A gas-liquid separator 4 and a steam dryer 5 are installed above the core 2. The steam heated in the core 2 passes through a gas-liquid divider 4 and a steam dryer 5. It is sent from the main steam line 6 to a turbine system (not shown).Condensate returned from the turbine system via a condenser is purified and then supplied to the reactor pressure vessel 1 from the water supply line 7 again.

By the way, the water diverted from the jet pump 3 flows from the recirculation pump 9 and the valve 10 through the reactor recirculation fins 8 and into the jet pump 3 again. This recirculation fin 8 is for recirculating the reactor water.
It has a winding piping structure.

In addition, the reference numeral 11 in the figure is reactor D: gas line for force adjustment;
12 also indicates a pump for the gas line 11, and 13 indicates a gas pressure regulator.

[Problem in the Background Art 1 However, no method has been found for removing radioactivity from the inner surface of the reactor recirculation line 8 in the above-mentioned nuclear reactor system, but recently, methods using various chemicals have been developed. Chemical decontamination methods are beginning to be developed. This decontamination method uses chemicals such as weak acids, weak salt salts, or chelating agents, and uses radioactive metal ions (
For example, Nishiki C62+! There is a method of decontaminating the oxide film (e.g. "Mrl") by dissolving it together with the oxide film.

However, in this method, due to the structure of the reactor system piping, it was not possible to prevent the decontamination liquid from flowing inside the piping. For this reason, odors (+, L
The oxide film with 11 particles was not dissolved efficiently. Therefore, the inner surface of the reactor system piping, which is the object to be decontaminated, was not uniformly decontaminated.

In addition, an attempt is made to dissolve the undissolved oxide film, and C decontamination fruit 7Il! If the time is increased, a problem arises in that the piping base metal (B) is attacked in the portion (C) where the oxide film has already been dissolved.

[Object of the Invention] The present invention has been made to solve the above problems,
BWR Plan] Reactor system ISi is an efficient chemical decontamination method for the reactor system that can be uniformly decontaminated! The object of the present invention is to provide a method for decontaminating pipes.

[Summary of the Invention] The present invention provides a method for chemically decontaminating the inner surface of the reactor system piping of a boiling water nuclear power station, including flowing a chemical decontamination liquid into the reactor system piping. This is a method for decontaminating nuclear reactor piping, which is characterized by blowing air bubbles into the chemical decontamination liquid.

[Embodiments of the Invention] Examples of the present invention will be explained with reference to Figure II1 above. As described above in the accompanying drawings, the lower part of the reactor pressure vessel 1 is provided with an inlet 8a and an outlet 8b of the reactor circulation line 8. The reactor water is circulated and agitated through this line 8 and the jet pump 3.In order to decontaminate the inner surface of the reactor reconsolidation line 8, decontamination liquid and water are added to the recirculation line 8 as follows. A gas supply line is provided.In addition, a bypass line 14 is provided in the recirculation line 8, and a switching valve 15 is interposed in this bypass line 14.A decontamination liquid injection port 16 and a gas inlet are provided in the bypass line 14. A decontamination liquid supply line 22 having a decontamination liquid supply pump 21 and a valve 25 is connected from the decontamination liquid tank 18 to the decontamination liquid injection port 16. gas cylinder 19
A gas supply line 20 having a valve 24 is connected thereto.

Thus, the recirculation line 8 is filled with decontamination liquid from the decontamination liquid tank 18 through the decontamination liquid tank 16 .

Next, the gas in the gas cylinder 19 is blown into the recombination line 8 through the gas inlet 17. At least one gas selected from nitrogen, oxygen, hydrogen, or argon is used as this gas to maintain the state of the oxide film on the piping. It is desirable to use sintered metal for the gas inlet 17, which has a great effect of making gas bubbles. It is desirable that the gas inlet 17 be installed at a plurality of locations so that air bubbles flow throughout the reactor recirculation line 8. By introducing air bubbles into the decontamination liquid in this manner, it is possible to cause the decontamination liquid to move, thereby increasing the stirring effect. In addition, the cleaning effect of the bubbles themselves is added, and the decontamination effect is significantly better than that of conventional methods. Further, as the decontamination liquid flows, the inner surface of the pipe is uniformly decontaminated, and as a result, there is no opening for corrosion of the pipe metal, and material deterioration can be prevented.

Next, a specific embodiment of the method of the present invention for -C decontamination by supplying a decontamination liquid while feeding air bubbles into a recirculation line will be described below. The target is the reactor system of the BWR plant, specifically the decontamination of the reactor recirculation line ε3. A chemical decontamination solution for this decontamination is poured into a small area a by one line. This chemical decontamination liquid then flows into the reactor recirculation lines 8a J) and 1811.
1. In order to prevent gas from flowing into the reactor pressure vessel 1, gas is forced into the reactor pressure vessel 1 at a constant pressure. For this reason, during the chemical decontamination period, Φ of the gas blown into the decontamination liquid as bubbles is extracted from the gas pressure control valve 13 in the reactor pressure vessel to keep the gas pressure in the reactor pressure vessel 1 constant. to η. The results of decontamination conducted using this method are shown in the table below. This is shown in comparison with the results of the conventional method, that is, a method that does not blow air bubbles into the decontamination solution.

Δ, B, C1D, E to examine the radioactivity removal effect lj
The radiation dose on the pipe surface was measured at point 5B.

In the present invention, the radiation dose decreased to 3 to 10IIIR/hr after decontamination at the five measured points.

Compared to the conventional method, which is 5 to 351 R/hr as shown in the table, the decontamination effect of the present invention is increased, and the radiation ω is reduced to the extent of C in each location. γ is praised.

[Effects of the Invention] According to the present invention, the decontamination time can be shortened by blowing air bubbles into the decontamination liquid, and the inner surface of the target piping can be uniformly decontaminated. It has the effect that the decontamination liquid does not attack the base metal and does not have any adverse effects on the materials.

[Brief explanation of the drawing]

The figure is a small system diagram of one nuclear reactor system of BWR/Run 1- for explaining the method of decontaminating reactor system piping according to the present invention. 1......Reactor pressure vessel 2...
......Furnace core 3...Jet pump 4...
...... Gas-liquid separator 5 ......
・Steam dryer 6... Main steam line 7... Water supply line 8...
・・・・・・Reactor recirculation line 9・・・・・・・・・
... Recirculation pump 10 ...... Valve 11 ...... Gas supply line for reactor pressure adjustment 12 ...... ... Gas supply pump 13 for reactor pressure adjustment ... Gas pressure control valve 14 ...
・・・・・・・・・Bypass line 15・・・・・・
・・・・・・Switching valve 16・・・・・・・・・・・・
Decontamination liquid injection dust 17... Gas inlet a ...... Decontamination liquid filling range △,
B, C, D, E -M Ray m +11 Localization 16

Claims (2)

[Claims] (1) In a method of chemically decontaminating the inner surface of the reactor system piping of a boiling water nuclear power plant, a chemical decontamination liquid flows into the reactor system piping, and air bubbles are formed in the chemical decontamination liquid. A method of decontaminating nuclear reactor system piping characterized by injecting. (2) The method for decontaminating nuclear reactor system piping according to claim 1, wherein the gas to be blown is at least one type of gas selected from air, nitrogen, oxygen, hydrogen, and argon.