JPS61129598A - Method of inhibiting storage of radioactivity to nuclear reactor primary system - 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 reactor primary system in which an oxide film is formed on the inner surface of the reactor primary system equipment and piping in a boiling water nuclear power plant (hereinafter referred to as a BWR plant). The present invention relates to a radioactive M product suppression method.

[Technical background of the invention and its problems] Generally, in an 8WR plant, an oxide film is formed on the inner surface of equipment and piping used in the reactor primary system because the plant is exposed to high temperature water during plant output operation. . When this oxide film is formed, radioactive metals in the reactor water, such as
Cobalt-60, cobalt-58, manganese-54, etc. are incorporated into the coating and increase the radiation m rate on the inner surface of the reactor primary system equipment and piping.

This is known to lead to increased radiation exposure for workers who inspect reactor system equipment and piping during regular plant inspections. Efforts have been made to reduce the concentration of radioactive metals in reactor water as a target for reducing the radiation dose rate of primary reactor equipment and piping. It is being implemented in an actual plant.

However, these measures have not necessarily been able to sufficiently reduce the radiation dose rate on the surfaces of equipment and piping.

On the other hand, as another method to reduce the radiation dose rate of equipment and piping, an oxide film is formed on the inner surface of equipment and piping before radioactive metal substances are generated, and the One possible method is to reduce the rate of oxide film formation on the inner surface and to suppress the amount of radioactive metal substances incorporated into this oxide film.

However, in order to put this method of forming an oxide film into practical use, especially in a BWR plant, it is necessary to secure a heat source and supply dissolved oxygen for the oxidation treatment, but it is difficult to operate other systems. There are many situations where we have no choice but to depend on them. Therefore, it can be imagined that major operational problems will arise during the construction and trial run of a BWR plant.

[Objective of the Invention] The present invention was conceived in view of this point, and it is possible to prevent radioactive metals such as cobalt-60, cobalt-58, manganese-54, etc. from being accumulated on the inner surfaces of piping and equipment of a BWR plant, and to reduce the radiation WAm rate. An object of the present invention is to provide a method for suppressing the accumulation of radioactivity in the primary system of a nuclear reactor, which prevents workers from being exposed to radiation without increasing the amount of radioactivity.

i "Summary of the Invention" In order to achieve the above object, the present invention provides a recirculation system (P
(LR) pump continuously recirculates the reactor water, and the Joule heat generated during operation of the PLR pump maintains the reactor water filled in the reactor at the BWR plant normal operating temperature before the nuclear heating of the reactor, and By maintaining the dissolved oxygen concentration under the same conditions, an oxide film is formed on the inner surface of the reactor primary system equipment and piping before the nuclear heating of the plant, and radioactive metal materials generated after the nuclear heating of the reactor plant are removed. This is a method of suppressing the accumulation of radioactivity in the primary system of a nuclear reactor, which suppresses accumulation on the piping surface.

Examples of the invention] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

The figure is a basic system diagram of a BWR plant.

In normal plant nuclear heating operation, steam generated by the nuclear heating material in the core 2 located in the reactor 1 is transferred to the main steam line 3.
, which rotates the turbine 4 and drives the generator 5 to supply electricity. The steam after doing work in the turbine 4 becomes condensed water in the main condenser 6. The condensate is purified by a condensate purification device 7, heated by a feed water heater 8, and returned to the reactor 1, forming a circulation system.

In the present invention, the above system is used, but the method of use is completely different from normal nuclear heating operation. The goal is to operate the reactor under normal BWR operating conditions, which remove radioactivity from the reactor water, without burning the nuclear fuel in the reactor core 2. That is, the Joule heat generated by operating the PLR pump 9 without using the nuclear fuel in the reactor core 2 raises the water temperature to the same temperature as under normal BWR operating conditions, and oxygen is supplied using the reactor water sampling line 10. The aim is to continue operation for N hours with the dissolved oxygen concentration in the reactor water being the same as under normal BWR operating conditions.

The present invention is carried out, for example, as follows.

Fill the reactor with water to below the level of main steam line 3.

At this time, the water supply stop valve 11 is kept closed. Next, the main steam isolation valve 12 and the turbine bypass valve 13 are opened by the main steam stop 14.
The reactor system and turbine system are maintained in a vacuum by closing the reactor system and operating the vacuum pump 15. hot well 16
The hot well 1 is filled with water and passed through the condensate purification device 7 by operating the condensate pump 17, purifying the water.
Perform angular circulation operation to return water to step 6. This hot well 1
Since the turbine gland seal water flows into the turbine gland 6, the excess water passes through the condensate purification device 7 and is collected in the condensate tank 18. Thereby, the water circulating through the bot well 16 can be maintained in a state of low dissolved oxygen.

Next, the reactor water is heated by Joule heat generated by continuous operation of the PLR pump 9, dissolved oxygen in the reactor water is degassed through the main steam line 3, and the dissolved oxygen concentration is adjusted under the BWR energized operating conditions. be equal to or less than. Thereafter, the main steam isolation valve 12 is closed, the control rod drive pump 19 is operated, and degassed condensate is injected from the control rod drive mechanism 20 until the reactor 1 is full. This method of injection into the reactor results in dissolved oxygen in the reactor water being equal to or lower than dissolved oxygen levels under normal BWR operating conditions.

If the dissolved oxygen is below the BWR normal operating conditions, dissolved oxygen is injected from the reactor water sampling line 10 to maintain the dissolved oxygen level equivalent to the 8WR normal operating conditions. Purification of the reactor water is carried out by the reactor purification system 21, and the reactor water quality is maintained in the same manner as under normal BWR operating conditions.

Through these operations, dissolved oxygen and water quality in the reactor water are reduced to B.
WR PL with maintenance control under normal operating conditions
BW is increased by continuous operation of R pump 9 and pump Joule heat.
R Increase the temperature to normal operating conditions.

The water temperature is balanced by draining high-temperature reactor water into the main condensate volume 14 through the reactor purification system 21 and injecting condensate from the control rod drive mechanism 20 for 6920 minutes.

In this way, the Joule heat generated by the continuous operation of the PLR pump 9 can be used to maintain and control the reactor water quality under the same conditions as under normal BWR operation.

By continuing this operation for about 100 hours or more, an oxide film is formed on the surfaces of the reactor primary system equipment and piping 22 and on the inner surface of the reactor before the nuclear heating of the plant occurs, that is, in the absence of radioactive metal 1. I can do it.

[Effects of the Invention] As explained above, by forming an oxide film by the method of the present invention before nuclear heating, the formation of an oxide film is suppressed after the nuclear heating of the plant. The amount of radioactive metal that accumulates on the surface of the reactor primary system equipment/piping 22 and the reactor during the formation stage is similarly suppressed. As a result, the increase in radiation dose rate to the inner surface of the reactor primary system equipment and piping is suppressed, and the radiation exposure of plant workers is reduced, which is an extremely useful effect on BWR plant operation.

[Brief explanation of the drawing]

The figure is a system diagram for explaining an example of the method for suppressing radioactivity accumulation in the primary system of a nuclear reactor according to the present invention.

Claims (1)

[Claims] (1) A nuclear reactor primary system characterized by forming an oxide film on the inner surface of reactor primary system equipment and piping using Joule heat generated during operation of a reactor water recirculation pump in a boiling water nuclear power plant. Method for suppressing radioactivity accumulation in the system.