JPH0318795A - Reactor - 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 [Industrial Application Field] The present invention relates to a nuclear reactor equipped with a reactor moderator cover gas device that uses heavy water or light water as a moderator. The present invention relates to a nuclear reactor equipped with a reactor moderator cover gas device suitable for preventing nuclear power generation.

(Conventional technology) Conventionally, reactor moderator cover gas devices have been designed to prevent deterioration of the moderator, and since the cover gas is used in areas with high radiation density near the reactor, chemically An inert gas is used that is stable and difficult to activate.In addition, in nuclear reactors that use heavy water or light water as a moderator, the moderator is decomposed by radiation, producing deuterium or hydrogen (hereinafter referred to as hydrogen) and oxygen. and is released into the cover gas.

At this time, when the hydrogen and oxygen concentrations in the cover gas fall within a certain range, hydrogen and oxygen react violently, causing a hydrogen explosion. For this reason, in the commentary on the "Technical Standards for Nuclear Power Generation Equipment" (Ordinance of the Ministry of International Trade and Industry) (edited by the Agency for Natural Resources and Energy, Ministry of International Trade and Industry, Nuclear Power Generation Safety Management Division, Public Utilities Department), Article 32, Reactor Containment Vessel Facilities, etc. It is assumed that the hydrogen concentration in the reactor containment vessel is less than 4% and/or the oxygen concentration is less than 5%.

Furthermore, in a mixture of flammable gas and air (or oxygen), a concentration limit appears where flame propagation no longer occurs, whether the concentration of flammable gas is too low or too high. The explosive range of hydrogen or deuterium is 4 to 75 vofl%, and the Bureau of Mines' Z
"Flamma-bility Characterist of Combustible Gases and Steam"
ics of Combustible Gases
andVapours (1965) published in J.

From the above, the reactor moderator cover gas device is provided with hydrogen and oxygen processing equipment such as a recombiner, and the concentrations of hydrogen and oxygen in the cover gas are maintained at predetermined values or below.

For example, in a new converter reactor that uses heavy water as a moderator, a device that circulates helium is used as a reactor moderator cover gas device. This equipment (hereinafter referred to as this system) consists of a calandria tank (tank containing moderator), a heavy water cooling system,
Helium is circulated as a cover gas in the heavy water purification system and other heavy water-based equipment to prevent deterioration of heavy water, and the explosive gases of deuterium and oxygen produced by radiolysis of heavy water are recombined and returned to heavy water. Keep the plant cheap. An overview of this system is shown in Figure 2, and a diagram of its principle is shown in Figure 3. This system consists of a blower 1 (2 out of 4 spares), two blower separators 2 connected to the discharge side of the blower 1 via a discharge valve 1o, and an outlet side of the blower separator 2. two helium gas preheaters 3 connected to each other via a preheater inlet valve l1, and two recombiners connected to each outlet side of the helium gas preheater 3 via a preheater outlet valve 12. 4, two coolers 5 connected to the outlet sides of the recombiners 4 via recombiner outlet valves 13, and two coolers 5 connected to the outlet sides of the coolers 5 via the cooler outlet valves l4. A cover gas return pipe 15 connected to the portion of the calandria tank 9 above the moderator (heavy water) liquid level is connected to the inlet side of the blower 1 and the portion of the calandria tank 9 above the moderator liquid level via the suction valve 17. The cover gas outlet pipe 16 is connected to the cover gas outlet pipe 16. In this system with the above structure, the calandria tank 9
Helium gas, which is filled as a cover gas for the moderator (heavy water) 18, is supplied to the cover gas outlet pipe 16 and the suction valve 1.
7, the helium gas is sucked into the blower 1, and the helium gas discharged from the blower 1 is removed from the heavy water sealed in the blower 1 by a blower separator 2. The helium gas that has exited the blower separator 2 is then preheated in a helium gas preheater 3 and then guided to a recombiner 4, where deuterium and oxygen in the helium produced by radiolysis are transferred to the recombiner. By the catalyst in 4, it is recombined to become heavy water. The helium gas heated by the heat of binding is cooled by the cooler 5 and then returned to the moderator liquid level in the calandria tank 9 through the cover gas return pipe 15. This system keeps the deuterium concentration in the cover gas below about 3 no Q% during reactor operation, and even if one blower 1 stops, the standby unit is activated to keep the deuterium concentration in the cover gas at the explosive limit. We maintain safe operation of the reactor by maintaining the following conditions to prevent hydrogen explosions. Furthermore, in the invention described in JP-A No. 61-260195, as shown in FIG. 4, by using pure hydrogen gas as the cover gas, the hydrogen concentration of the cover gas is made to be above the hydrogen explosion range, and a hydrogen explosion is caused. At the same time, the oxygen generated by radiolysis is immediately recombined with hydrogen, reducing the release of oxygen into the cover gas (gas phase).

[Problem to be solved by the invention]

In the above conventional technology shown in Figure 2, processing equipment for (heavy) hydrogen and oxygen such as a recombiner is provided, but there are problems in terms of equipment costs, operating costs, etc., and operational operability. .

As a countermeasure to improve this, we have proposed a method for unexamined patent application published in 1986, as shown in Fig. 4.
The invention described in Publication No. 260195 has been proposed, but since pure (deuterium) hydrogen gas is used as the cover gas, hydrogen gas supply equipment is required, and hydrogen must be exhausted during maintenance etc. When handling, care must be taken to ensure that the hydrogen gas concentration does not reach the explosive range.

The object of the present invention is to reduce the amount of (heavy) hydrogen and oxygen generated by radiolysis while reducing the capacity of the hydrogen gas supply equipment described above and improving the handling of the cover gas. The goal is to reduce the capacity (especially the recombiner capacity).

[Means to solve the problem]

The above-mentioned problem is solved by a nuclear reactor equipped with a reactor moderator consisting of heavy water or light water and a container containing a moderator cover gas that covers the surface of the reactor moderator. This is achieved by using a mixed gas of an inert gas and hydrogen, setting the concentration of deuterium or hydrogen in the mixed gas to be below the hydrogen explosion limit, and setting the pressure of the mixed gas to a pressure exceeding 1 atmosphere.

The above problem is also solved by the nuclear reactor according to claim 1, which has means for maintaining the pressure in the gas phase of the container containing the reactor moderator and the reactor moderator cover gas at a pressure exceeding 1 atmosphere. is also achieved.

The above object is further achieved by the nuclear reactor according to claim 1 or 2, wherein a deoxo device is provided connected to the gas phase part of the container containing the reactor moderator and the reactor moderator cover gas. be done.

The above problem can also be solved by providing a blower device connected to the gas phase portion of the container containing the reactor moderator and the reactor moderator cover gas, and the discharge side of the blower device being connected to the liquid phase portion of the container. This can also be accomplished by a nuclear reactor according to claim 1 or 2, which is connected to a nuclear reactor.

The above problem can be further solved by reducing the concentration of deuterium or hydrogen in the reactor moderator cover gas to below the explosion limit and by increasing the pressure of the reactor moderator cover gas. This can also be achieved by increasing the concentration of hydrogen and suppressing the generation of oxygen gas due to radiolysis of the reactor moderator.

[Effect]

When water molecules, which are moderators, are irradiated with neutrons or gamma rays, the orbital electrons of the water molecules are ejected by Compton scattering and the photoelectric effect. These electrons initially have high energy and high speed when ejected, but due to electromagnetic interaction they lose energy and ionize other water molecules in an extremely small area.

As a result, following the ionization reaction of water molecules, D, O"') D"+OD+e-a g, D, ○D-? What will happen? In addition, D2,O is produced as a primary product, and the primary products further react with each other, resulting in O,,0
2-, Do. , Do, -, D,02 and other decomposition products are produced.

On the other hand, if the surface of the moderator under such conditions is covered with a high-pressure mixed gas of helium and deuterium D2, D2 will dissolve in the moderator in proportion to the partial pressure of deuterium D2, and near the water surface, etc. The following elementary reactions occur.

Each elementary reaction is 2D2+20D→2D20+2D D 102 →DO2 D +D02→D202 D20■ →2D○, and as a result of the apparent progression of 2D, +02→2D20, it reacts with oxygen. In the above reaction, ○D apparently acts as a catalyst, but D20 produced in the core becomes a source of ○D through the equilibrium reaction of D202 ″ 20D ← .

As described above, when the concentration of dissolved hydrogen in the moderator increases, oxygen generated by radiolysis of the moderator immediately recombines with hydrogen, reducing the release of oxygen into the cover gas (gas phase).

〔Example〕

A first embodiment of the present invention will be explained with reference to FIG.

The reactor shown in the figure has a moderator holding tank 9 which is a container containing heavy water 18 which is a moderator and a moderator cover gas 19.
, a pressure pipe 8 provided vertically penetrating the moderator storage tank 9, and a nuclear fuel 7 housed in the pressure pipe 8;
It is equipped with The heavy water T8 is not filled into the moderator holding tank 9, in order to allow the liquid level to fluctuate due to temperature fluctuations, etc.
A space is left at the top, and the moderator cover gas (
19 (hereinafter referred to as cover gas) is filled.

A gas phase portion of the moderator storage tank 9 is supplied with a cover gas supply pipe 24 and a pressure regulating valve 22, 23 as a means for maintaining the pressure of the gas phase portion at a pressure exceeding 1 atmosphere (absolute pressure).
A high-pressure vessel 20 containing high-pressure helium and a high-pressure vessel 21 containing high-pressure deuterium are connected to each other.

In this nuclear reactor, neutrons emitted from the nuclear fuel in the pressure tube 8 are decelerated by heavy water outside the pressure tube, and then become thermal neutrons, causing a chain reaction in the nuclear fuel 7. The heat generated in the nuclear fuel 7 by the chain reaction is transmitted to the coolant flowing in the pressure pipe 8, transferred outside the nuclear reactor, and used for a desired purpose.

The cover gas 19 is a mixture of helium and 3 moQ% deuterium, and the pressure is maintained at 70 kg/cd (absolute pressure) by the pressure regulating valves 22 and 23. At this time, since the concentration of deuterium gas in the cover gas is 3moQ%, the partial pressure of deuterium gas is 70X0.03=2.1
kg/cii, and the solubility of deuterium gas in heavy water is more than double that of the example described in JP-A-61-260195 in which pure deuterium gas was used as a cover gas at atmospheric pressure.
The recombination effect of deuterium and oxygen in heavy water is improved. Therefore, the oxygen concentration in the heavy water and the cover gas becomes saturated at a low value, and the oxygen concentration in the cover gas is maintained below the explosive limit without using deuterium and oxygen processing equipment such as a recombiner.

In the second embodiment shown in FIG. 5, a deoxo device IO for removing oxygen is connected to the gas phase portion of the moderator holding tank 9.
The cover gas 9 is configured to circulate between the gas phase portion of the moderator holding tank 9 and the deoxo apparatus. In this embodiment, of deuterium and oxygen produced by radiolysis of the moderator, only oxygen is removed by the deoxo unit 110, and the concentration of deuterium gas increases. In order to prevent the concentration of deuterium gas from exceeding the hydrogen explosion limit, the pressure of the cover gas is adjusted by a cover gas pressure adjustment means (not shown), and the progress state of recombination is adjusted.6 In this embodiment, Since deuterium produced by radiolysis is used as deuterium for recombination, there is no need for initial filling of deuterium gas.

FIG. 6 shows a third embodiment of the present invention, and the nuclear reactor shown in this figure is provided with a plurality of tubular protrusions 25 at the top of the moderator holding tank 9 that protrudes upward from the tank. The top of the gas phase forms the gas phase containing the cover gas. The suction side of a blower 1, which is an air blower, is connected to the gas phase section through a cover gas take-off pipe 16 and a suction valve 17, and the discharge side of the blower 1 is connected to the moderator storage tank 9 through a cover gas return pipe L5A. Connected to the bottom. The pressure pipe 8 containing fuel is installed in the same manner as in the first embodiment, but its explanation will be omitted.

In this embodiment, the cover gas held at high pressure in the gas phase inside the tubular protrusion 25 is sucked by the blower 1, and
The moderator is blown into the bottom moderator of the moderator holding tank 9. In the process of the cover gas rising from the bottom of the tank to the gas phase of the tubular protrusion 25, deuterium in the cover gas dissolves into the moderator, increasing the dissolved deuterium concentration, and causing the oxygen generated by radiolysis to increase. Deuterium recombination occurs quickly.

In the first to third embodiments described above, since a recombiner is not provided, the equipment is simple, and furthermore, since oxygen and deuterium are recombined in the moderator, the concentration of dissolved oxygen in the moderator is As a result, corrosion of members in contact with the moderator is reduced. Further, even if the cover gas leaks to the outside, the deuterium gas concentration in the cover gas is below 4 moQ% (hydrogen explosion limit), and there is no risk of a hydrogen explosion after the leak.

〔Effect of the invention〕

According to the present invention, in a nuclear reactor using heavy water or light water as a moderator, the moderator cover gas is a mixed gas of an inert gas and deuterium or hydrogen at a concentration below the hydrogen explosion limit, and the mixed gas pressure is 1. Since it is used at a pressure above atmospheric pressure (absolute pressure), the concentration of dissolved deuterium or hydrogen in the moderator increases without increasing the concentration of deuterium or hydrogen in the cover gas, and the oxygen generated by radiolysis is removed from the moderator. in,
It is possible to reduce the amount of oxygen gas released into the cover gas by recombining it with deuterium or hydrogen, and the capacity of the recombiner to recombine deuterium or hydrogen and oxygen in the cover gas. This has the effect of simplifying equipment by reducing or omitting it.

[Brief explanation of drawings]

FIG. 1 is a system diagram including a sectional view of the first embodiment of the present invention;
2, 3, and 4 are sectional views and system diagrams showing the prior art, FIG. 5 is a system diagram including a sectional view showing a second embodiment of the present invention, and FIG. 6 is a system diagram including a sectional view showing the second embodiment of the present invention. FIG. 3 is a system diagram including a cross-sectional view showing a third embodiment of the present invention. 1... Air blower (blower), 9... Container (tank holding moderator), 10... Deoxo device, 18... Moderator, 19... Cover gas, 20.21... High pressure Container, 22, 23...pressure regulating valve.

Claims (1)

[Claims] 1. In a nuclear reactor equipped with a reactor moderator made of heavy water or light water and a container containing a moderator cover gas that covers the surface of the reactor moderator, the moderator cover gas is an inert gas. and deuterium or an inert gas and hydrogen; the concentration of deuterium or hydrogen in the mixed gas is below the hydrogen explosion limit; and the pressure of the mixed gas exceeds 1 atmosphere. A nuclear reactor characterized by: 2. The nuclear reactor according to claim 1, further comprising means for maintaining the pressure in the gas phase of the container containing the reactor moderator and the reactor moderator cover gas at a pressure exceeding 1 atmosphere. 3. The nuclear reactor according to claim 1 or 2, further comprising a deoxo device connected to a gas phase portion of a container containing a reactor moderator and a reactor moderator cover gas. 4. A blower device is provided connected to the gas phase portion of the container containing the reactor moderator and the reactor moderator cover gas, and the discharge side of the blower device is connected to the liquid phase portion of the container. The nuclear reactor according to claim 1 or 2, characterized in that: 5. Lower the concentration of deuterium or hydrogen in the reactor moderator cover gas to below the explosion limit and increase the pressure of the reactor moderator cover gas to reduce the concentration of dissolved deuterium or hydrogen in the reactor moderator. A method to suppress the generation of oxygen gas due to radiolysis of nuclear reactor moderator