JPH01110294A - Structural material of reactor primary cooling system - Google Patents

Abstract

PURPOSE:To prevent the accumulation of radioactivity by forming a metal film on the surface of a structural material coming in contact with coolant. CONSTITUTION:A separable metal film layer or more of noble metal and the like such as austenite stainless steel or platinum are formed on the inner surface of various apparatuses and a tubing of a boiling water reactor 1, a reactor condensing system 24, a reactor water feeding system 23, a reactor recirculating system 25 and a reactor cooling and purification system 33 in the structures of a reactor primary cooling system. Therefore, since the noble metals are not corroded, radioactivity is not accumulated. Since in the case of austenite stainless steel a tubing is disassembled and metal films are separated when the radioactivity level of corrosion films formed as surface layers exceeds prescribed level, the radioactivity can be removed up to approximately 100% and produced waste quantity is small.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to a structural material for a nuclear reactor primary cooling system, and in particular, the present invention relates to a structural material for a nuclear reactor primary cooling system, and in particular, to prevent radioactivity The present invention relates to a structural material for a nuclear reactor primary cooling system suitable for reducing accumulation.

(Prior art) In general, particulate and ionic radioactivity circulates in the primary cooling system of a boiling water nuclear reactor, and the radioactivity accumulates on the inner surface of the primary cooling system structure through various mechanisms. increasing radiation dose rates in structures.

For example, in a stainless steel structure with the largest wetted surface area among primary cooling system structures, high-temperature, high-pressure water (70 atm, 2
(50°C or higher), a corrosive oxide film containing iron, chromium, and nickel as main components is formed on the inner surface of stainless steel.

Ionic radioactivity is taken in during the growth of the corrosive oxide film. This ionic radioactivity may also be incorporated by isotope exchange as described below.

60co2++co, 60co+co2+Furthermore, particulate radioactivity accumulates in the form of deposits on the corroded oxide film.

In other words, the presence of this corrosive oxide film causes ionic and particulate radioactivity to accumulate on the inner surface of the reactor primary cooling system structure. As a result, when inspecting the reactor primary cooling system, there is a risk that workers performing the inspection work may be exposed to radiation.

There is also the problem that maintenance costs increase in order to avoid exposure to radiation.

(Problem to be solved by the invention) Therefore, various methods have been researched to remove radioactivity by mechanically or chemically treating the surface of structural materials where radioactivity has accumulated, and some plants have actually It is carried out in However, these techniques are still under development and have not been established.

In other words, mechanical decontamination attempts to remove the film by polishing the surface, and although it is effective in a plant that is being dismantled, it is practically impossible in a plant that is in operation. on the other hand,
In chemical decontamination, a chemical solution is circulated to dissolve the surface film, and the radioactivity contained in the solution is recovered using ion exchange resin, etc., but it is commonly effective for various materials. It is difficult to select a chemical solution, and there are also reports that impurities that remain after decontamination due to the chemical solution not being completely cleaned can cause stress corrosion cracking. Additionally, chemical decontamination typically has a low radioactivity removal rate.

As described above, the decontamination methods currently being researched and considered not only pose considerable problems when implemented, but are also expected to require considerably large-scale equipment and costs when actually implemented.

The present invention was made in consideration of the above circumstances, and it is possible to prevent radioactivity from accumulating on the inner surface of the structural material of the reactor primary cooling system, and even if it does accumulate, it can be easily removed. It is an object of the present invention to provide a structural material for a primary cooling system of a nuclear reactor, which can reduce the amount of II exposed to workers during inspections, etc., and reduce maintenance costs.

[Structure of the invention]

(Means for Solving the Problems) The structural material of the nuclear reactor primary cooling system according to the present invention consists of a main steam system that guides the steam generated in the reactor to the turbine, and a main steam system that condenses the steam that has done work in the turbine. , a reactor condensate system and reactor water supply system that guide this condensate to the reactor, a reactor recirculation system that forcibly circulates the coolant in the reactor to the reactor core, and a reactor recirculation system that removes impurities generated within the reactor. In the structural materials of the reactor primary cooling system that constitutes the reactor primary cooling system, which includes a reactor coolant purification system that purifies the coolant, on the inner surface of the structural material that comes into contact with the coolant containing radioactive impurities. , - layer or multilayer metal film is formed.

(Function) Since a -layer or multilayer metal film is formed on the inner surface of the structural material of the reactor primary cooling system that comes into contact with the coolant containing radioactive impurities, a metal that does not corrode is used as the metal film. This can prevent radioactivity from accumulating on the inner surface of the structural material.

Further, when a corroding metal is used for the metal film, the radioactivity can be easily removed by peeling off the metal film in which radioactivity has accumulated. In this case, if the metal film is one layer, after removing the metal film, the metal film is formed again on the inner surface of the structural material. On the other hand, if the metal film is multilayered, only the negative layer can be peeled off and used as is.

In this way, it is possible to prevent radioactivity from accumulating on the inner surface of structural materials, and even if it does accumulate, it can be easily removed, reducing the amount of radiation exposure of workers during inspections, etc. Furthermore, maintenance costs can be reduced.

(Example) An example of the structural material of the nuclear reactor primary cooling system according to the present invention will be described with reference to the drawings.

FIG. 1 is a system diagram showing a nuclear reactor primary cooling system equipped with equipment and piping using the structural material of the nuclear reactor primary cooling system according to the present invention.

A reactor pressure vessel 3 of a boiling water nuclear reactor 1 includes a reactor core 5 and a coolant 7 therein.

The reactor core 5 generates heat by a nuclear reaction of nuclear fuel such as uranium, heats the coolant 7, and generates steam. The generated steam is separated from water in a steam/water separator (not shown) and then dried in a steam dryer (not shown). The dry steam is guided to a steam turbine 13 through a main steam system 11 consisting of a main steam pipe 9 and the like, and rotates the steam turbine 13.

The steam that has done work in the steam turbine 13 becomes condensed water in the condenser 15. This condensate is purified in a demineralizer 17, boosted in pressure by a feed water pump 19, heated through a feed water heater 21, and then introduced into the reactor 1. These condenser 15, demineralizer 1
7. Water supply pump 19 and condensate system pipe 2 connecting these
0 constitutes the reactor condensate system 24. Further, a reactor water supply system 23 is constituted by the water supply pump 19, the water supply heater 21, and the water supply system pipe 22 that connects the water supply pump 19, the water supply heater 21, and the reactor 1.

On the other hand, the water separated by the steam separator flows down and becomes integrated with the coolant 7, and the reactor recirculation system 25 forcibly circulates the coolant integrated with this water into the reactor pressure vessel 3. The reactor recirculation system 25 includes a jet pump 27 disposed in a downcomer section within the reactor pressure vessel 3, and a recirculation pump 31 connected to the jet pump 27 via a recirculation system pipe 30. . Lower plenum 29 of reactor pressure vessel 3
The cooling water inside is passed through a recirculation system pipe 30 to a recirculation pump 31.
The pressure is increased by the jet pump 27, and the water becomes the driving water.
It is squirted on top of the. Due to the depressurizing effect of this jet flow, water as a coolant in the reactor pressure vessel 3 reaches the lower plenum 29 via the jet pump 27, and is guided to the reactor core 5 from there.

Further, the water as a coolant in the lower plenum 29 is transferred to the demineralizer 3 through the purification system pipe 34 of the reactor coolant purification system 33.
Guided to 5th class. The coolant 7 has impurities removed by a demineralizer 35, and is then supplied into the reactor 1 via a purification system pipe 34 and a water supply pipe 22.

By the way, among the structures of the reactor primary cooling system, various equipment of the boiling water reactor 1, the reactor condensation system 24, the reactor water supply system 23, the reactor recirculation system 25, and the reactor coolant purification system 33, The piping is in contact with water as a coolant. The parts that come into contact with the liquid are mainly made of stainless steel.

In this example, on the inner surfaces of the various devices and piping mentioned above,
- forming layered or multilayered peelable metal films; As a metal film, the inner body of the film does not corrode and no film is formed.
It is best to use a metal that does not become radioactive even if it is eluted into the coolant and brought into the reactor 1, and does not absorb neutrons. However, in actual application, all There is no need to be prepared. Specifically, austenitic stainless steel is suitable for the metal film.

With austenitic stainless steel, it is possible to industrially produce thin plates of 0.05 m or less at the current technological level. The metal film layer is formed by, for example, lining the inner surface of the primary pipe or the like with a thin plate of austenitic stainless steel. When the metal films are formed in multiple layers, they are formed so that they can be mutually peeled off.

Next, the operation of the above embodiment will be explained.

Normally, during the operation of an atomic coupler, dissolved oxygen is approximately 200p1)b and dissolved hydrogen is approximately 25p due to radiolysis of water.
PB is present, and when a plant is operated for a certain period of time in this environment, a corrosion film is formed on the surface of the metal film, and radioactivity is taken in.

This corrosion film is caused by the alloy components of the austenitic stainless steel diffusing to the surface of the metal film, where they combine with the m element in the coolant and depositing on the surface, and is a black or red oxide film.

If the radioactivity contained in the corroded film exceeds the permissible level due to continued operation of the plant, the piping section will be disassembled and the metal film will be peeled off and recovered. Since radioactivity is contained in the gold bottom film, it is possible to remove nearly 100% of radioactivity. The removed metal membrane is solid waste, but because it is very thin, it can be made very compact by compression processing, and it is much smaller than the total volume of waste generated by conventional decontamination methods. be.

After removing the decontaminated metal film, if the structure is a multi-layer metal film, the piping section is reassembled, and if it is a negative layer, it is lined with a new metal film.

According to the above embodiment, radioactivity accumulated on the inner surface of the reactor primary cooling system piping, etc. can be easily removed.
It is possible to reduce the radiation exposure of workers during inspections and the like, and it is also possible to reduce maintenance costs.

In addition, by forming a metal film on the inner surface of the piping in the primary cooling system, there is no need to use stainless steel as the piping material for the primary cooling system. can be used. Therefore, it becomes possible to reduce production costs.

In the above embodiments, austenitic stainless steel was used as the metal film, but noble metals such as platinum may also be used as the metal film. When noble metals are used, since they do not corrode, almost no radioactivity accumulates in the metal film, so there is no need to disassemble and replace the metal film. Therefore, when a noble metal is used, the metal film may have a single layer structure. In other words, there are effects similar to those of the above embodiment.

〔Effect of the invention〕

The structural material of the reactor primary cooling system according to the present invention has a -layer or multilayer metal film formed on the inner surface of the structural material that comes into contact with the coolant containing radioactive impurities. It is possible to prevent radioactivity from accumulating on the inner surface, and even if it does accumulate, it can be easily removed.As a result, it is possible to reduce the amount of radiation exposure of workers during inspections, etc., and to reduce maintenance costs. can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a nuclear reactor primary cooling system equipped with an embodiment of the structural material of the nuclear reactor primary cooling system according to the present invention. 1... Boiling water reactor, 3... Reactor pressure vessel, 1
1... Main steam system, 13... Steam turbine, 15...
- Condenser, 23... Reactor water supply system, 24... Reactor condensate system, 25... Reactor recirculation system, 33... Reactor coolant purification system.

Claims (1)

[Scope of Claims] 1. A main steam system that guides steam generated in a nuclear reactor to a turbine, a reactor condensation system that converts steam that has done work in the turbine into condensate, and guides this condensate to a nuclear reactor, and a nuclear reactor. It has a water supply system, a reactor recirculation system that forcibly circulates the coolant in the reactor to the reactor core, and a reactor coolant purification system that purifies the coolant by removing impurities generated within the reactor. In the structural material of the reactor primary cooling system constituting the nuclear reactor primary cooling system, an atom characterized in that a single layer or multilayer metal film is formed on the inner surface of the structural material that comes into contact with the coolant containing radioactive impurities. Structural material for the furnace primary cooling system. 2. The structural material for a nuclear reactor primary cooling system according to claim 1, wherein the metal film is made of austenitic stainless steel and is formed to be peelable. 3. A structural material for a nuclear reactor primary cooling system according to claim 1, wherein the metal film is made of a noble metal such as platinum.