JPH09292491A - Flammability gas concentration reducer and its control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently process excess hydrogen gas when a large amount of hydrogen gas is produced in a severe accident in a flammability gas concentration reducer. SOLUTION: A plurality of flammability gas concentration reduces 100, are disposed in a reactor containment vessel houses a catalyst 1 for reacting hydrogen gas with oxygen gas in a housing vessel 3. The flammability gas concentration reducer 100 comprises a gas supply means having nozzles 3, tubing 4 and valves 6 for supplying gas containing oxygen to the catalyst 1, a concentration detection means having a detection tube 7 and a concentration meter 8 for detecting concentration of flammability gas (hydrogen and oxygen) in the containment vessel, and a control system (dotted line) for opening and closing the valves 6 on the basis of gas concentration detected with the concentration detection means. When excess hydrogen gas exists, oxygen gas is supplied to the housing vessel 3, and reacted with the excess hydrogen gas by the catalyst 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for reducing flammable gas in a nuclear reactor containment vessel and a control method when a severe accident exceeding a design standard occurs.

[0002]

2. Description of the Related Art In the safety design of a nuclear reactor, the following flammable gas is assumed to be generated in the containment vessel when a loss of coolant accident, which is considered as a design reference event, occurs. .

First, when the temperature of the fuel in the reactor pressure vessel rises, zirconium of the fuel coating material reacts with water to generate hydrogen gas. Further, the radioactive substance released from the broken portion of the pipe flows into the pressure suppression pool, and hydrogen gas and oxygen gas are generated by the radiolysis of water. In the boiling water reactor, the nitrogen gas in the reactor containment vessel is replaced during normal operation, so the initial oxygen gas concentration is 3.5.
% Or less.

FIG. 3 shows the relationship between the composition of hydrogen and oxygen and the flammability limit. Due to the accident, the concentrations of hydrogen gas and oxygen gas increase in the containment vessel. When the hydrogen gas concentration reaches 4% or more and the oxygen gas concentration reaches 5% or more, the flammability limit is reached as shown in the figure, and there is a risk of spontaneous ignition and loss of safety of the reactor containment vessel. Therefore, a combustible gas concentration control system for recombining hydrogen gas and oxygen gas is provided.

FIG. 2 shows an outline of a conventional combustible gas concentration control system in a boiling water reactor. The system configuration mainly includes a recombiner, and includes a blower 15, a heater 16, a thermal reaction recombiner 17, a cooler 18, a separator 19, piping valves, and a measurement controller. In the event of a coolant loss accident assumed in the design, the portable recombination equipment will be transported to the reactor building, and will be carried in and installed. Then, the gas in the reactor containment vessel 11 is sucked from the dry well 12 by the blower 15, and the hydrogen gas and the oxygen gas are recombined by the thermal reaction by the recombiner 17 via the heater 16. The vapor generated by the recombination reaction is condensed by the cooler 18 and then separated by the separator 19
The water is removed by and the remaining gas is returned to the wet well 13.

In addition to this, as a method for reducing the concentration of combustible gas at the time of an accident, as described in JP-A-3-200097 and JP-B-4-6950, There is an example in which a hydrogen absorbing device is installed in the middle of a pipe part including a portable recombining device installed outside. Further, as described in JP-A-58-135991,
An example is known in which a catalyst for oxidizing hydrogen gas is installed in the reactor containment vessel 11.

[0007]

If a severe accident that exceeds the accident event that should be assumed in the design occurs and a large amount of hydrogen gas is generated by the reaction between the molten debris and water, it is stored. The amount of hydrogen gas in the container is relatively larger than that of oxygen gas. Therefore, in the above-described recombining apparatus, even if the recombiner 17 causes the hydrogen gas and the oxygen gas to react with each other, excess hydrogen gas remains in the storage container 11. In this state, the non-combustible region shown in FIG. 3 is entered and combustion does not occur immediately, but anxiety about the operation of the reactor remains. However, the conventional recombination device has not considered the treatment of surplus hydrogen gas.

Further, since the conventional recombining device is installed outside the reactor containment vessel, a pipe for guiding the combustible gas and an isolation valve at the penetration portion of the containment vessel are required, so that the facility cost is reduced. Not only does it increase, but maintenance problems also increase. Furthermore, the portable recombining device requires a power source to operate the blower 15, the heater 16, the pump for supplying the cooling water to the cooler 18, and the like.

Further, even when a catalyst is installed inside the containment vessel as in Japanese Patent Laid-Open No. 58-135991, the effect of dust adhering to the catalyst during normal operation and the catalyst function during regular inspections, etc. There is a problem that the deterioration of can not be inspected.

A first object of the present invention is to provide a large amount of hydrogen gas such as a severe accident,
Efficiently process excess hydrogen gas in the reactor containment vessel,
An object of the present invention is to provide a combustible gas concentration reducing device and a control method thereof.

A second object of the present invention is to provide a highly reliable flammable gas concentration reduction device which facilitates prevention of deterioration of the flammable gas treatment function or maintenance and inspection.

[0012]

A first object of the present invention is to provide a catalyst for reacting hydrogen gas and oxygen gas, and a storage container storing the catalyst, and a plurality of flammable materials arranged in the reactor containment vessel. In the gas concentration reducing device, this is achieved by disposing a hydrogen gas absorber below the catalyst in the storage container.

As a function of this configuration, the heat of reaction between hydrogen and oxygen in the catalyst forms a circulating flow of gas in the storage container, and the amount of flammable gas flowing into the storage device increases. Therefore, by installing the hydrogen gas absorber in the storage container, it becomes easy to absorb the hydrogen gas. Furthermore, the gas temperature rises at the catalyst outlet due to the reaction heat of hydrogen and oxygen. However, since the hydrogen absorber is provided below the catalyst, it is possible to prevent the hydrogen gas from being released again from the absorber due to the temperature rise.

According to this, even if a relatively large amount of hydrogen gas is generated during a severe accident, the hydrogen gas is temporarily
The hydrogen gas concentration can be reduced by selective absorption by the hydrogen gas absorber, and the reaction with the catalyst is performed after bringing the ratio of hydrogen and oxygen close to each other. Therefore, the excess hydrogen gas can be efficiently reduced with an extremely simple configuration.

The above first object can also be achieved by the following configuration according to the present invention. That is, in a combustible gas concentration reducing device having a catalyst for reacting hydrogen gas and oxygen gas and a storage container containing the catalyst, and a plurality of flammable gas concentration reducing devices arranged in the reactor containment vessel, oxygen or a gas containing oxygen is added to the catalyst. An oxygen gas supply means for supplying and a concentration detection means for detecting the concentration of the flammable gas (hydrogen and oxygen) in the storage container are provided, and the oxygen gas is supplied by the oxygen gas supply means based on the detected gas concentration. It is achieved by controlling.

According to this, the concentration detecting means detects that the hydrogen gas concentration is relatively higher than the oxygen gas concentration. In the oxygen gas supply means for supplying oxygen gas or air containing oxygen, when the hydrogen gas concentration is high, the oxygen gas is supplied into the storage container containing the catalyst according to the ratio with the oxygen gas, and the excess catalyst is used. By reacting with hydrogen gas,
Excess hydrogen gas can be treated efficiently.

The above-mentioned second object is that in the apparatus for reducing the concentration of combustible gas for the above-mentioned first object, the inlet / outlet portion of the storage container which is in a closed state during the normal operation is inside the storage container at the time of an accident. This is achieved by having a mechanism that detects an increase in temperature or pressure and releases the pressure.

According to this, the entrance / exit of the storage container, which is closed during normal operation, has a mechanism for detecting an increase in temperature or pressure in the storage container at the time of an accident and opening it. It is possible to prevent dusts during operation from adhering to the surface of the catalyst and prevent functional deterioration of the catalyst that acts in the event of an accident.

The second purpose is to provide a test gas supply means for supplying a combustible gas of a known concentration below the catalyst and an upper part of the catalyst in the combustible gas concentration reducing apparatus for the above first purpose. It is achieved by providing a means for detecting the hydrogen gas concentration.

According to this, at the time of periodical inspection of the nuclear power plant, the inspection gas is supplied from below the catalyst with the inlet / outlet portion of the storage container closed, and the catalyst reacts the inspection gas to cause the storage container to react. By detecting the hydrogen gas concentration at the outlet, the reaction efficiency of the catalyst can be evaluated, and the inspection and inspection of the combustible gas concentration reduction device becomes easy.

The above-mentioned respective configurations of the present invention can be appropriately combined.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a plurality of embodiments of the present invention will be described in detail with reference to the drawings.

[Embodiment 1] Embodiment 1 mainly corresponds to the first object, and will be described with reference to FIGS. 1 and 3 to 7.

FIG. 1 shows a schematic structure of a combustible gas concentration reducing device. In the apparatus 100 for reducing the concentration of combustible gas, the catalyst 1 is arranged in the storage container 3 and fixed by the support structure 2. As the material of the catalyst 1, as is well known in the art,
Platinum or palladium, which can operate even when the concentration of combustible gas is low, shall be used. The catalyst 1 is formed into a plurality of plates and has a structure in which flammable gas flows through the gaps between the plates. In order to reduce the flow resistance when the flammable gas flows, the catalyst 1 may have a wire mesh structure.

A pipe 4 and a nozzle 5 for supplying a gas containing oxygen (for example, air) are provided below the catalyst 1, and a flammable gas concentration detector 8 and its detector are provided at the entrance of the storage container 3. A detection pipe 7 is provided, and a control system (abbreviated with a dotted line) for adjusting the opening degree of the valve 6 provided in the pipe 4 based on the detected hydrogen gas / oxygen gas concentrations is also provided.

FIG. 4 shows the internal structure of the reactor containment vessel in which the combustible gas concentration reducing device is arranged. Primary containment vessel 11
Inside, more storage containers 3 of the combustible gas concentration reducing apparatus 100 are arranged above the dry wells 12 and the wet wells 13 where hydrogen gas easily collects. this house,
The storage container 3 arranged in the dry well 12 is arranged opposite to the inlet pipe portion of the heat exchanger 30 in the cooling water pool 34 outside the reactor containment vessel 11.

As means for supplying oxygen gas to the storage container 3, the reactor containment vessel 1 which is normally replaced with nitrogen gas is used.
A containment vessel air-conditioning system that exhausts nitrogen gas and raises the oxygen concentration is used so that an inspector can enter during the regular inspection. That is, the blower 22 of the containment vessel air conditioning system, the pipes 23 and 24, and the pipe 4 of the combustible gas concentration reducing apparatus 100 are connected. Alternatively, a small air cylinder or oxygen cylinder may be installed in the storage container 11 and connected to the pipe 4.

By the way, in a design standard accident such as a loss of coolant accident, it is assumed in the safety analysis that 0.73% of zirconium present in the core reacts with water. For example, in the case of a 1.3 million kWh class reactor, about 150
Hydrogen gas of Nm ³ is generated. In the radiolysis of water, 16N after 1000 seconds from the reactor scrum.
Hydrogen gas of m ³ / h (half that of oxygen gas) is generated, but the gas generation amount decreases with time. The amount of hydrogen gas generated by this water-metal reaction and radiolysis is very smaller than the volumes of the dry well 12 and the wet well 13 in the storage container 11. Therefore, the initial hydrogen gas concentration is about 3% on the dry well 12 side, and the rate of increase in the hydrogen gas concentration thereafter becomes slow. The initial oxygen gas concentration in the storage container 11 is maintained at about 3.5% or less because it is replaced with nitrogen gas during normal operation, and then the oxygen gas concentration gradually increases due to radiolysis.

In this embodiment, the container 3 accommodating the catalyst 1 which operates from a concentration lower than the flammability limit (hydrogen gas concentration 4% or more and oxygen gas concentration 5% or more) shown in FIG. Since a large number are arranged in the upper position of, the low concentration hydrogen gas and oxygen gas generated in the design standard accident react with the catalyst 1. Therefore, hydrogen gas can be processed without supplying oxygen gas from the gas supply pipe 4.

Next, it is assumed that molten debris reacts with water to generate a large amount of hydrogen gas and steam, as in a severe accident. The strictest assumption is that if the reaction rate of water and zirconium is 100%, it will be about 200.
Since hydrogen gas of 00 Nm ³ (about 900 kg) is generated, the hydrogen gas concentration sharply increases. In this case, since the hydrogen gas concentration is relatively higher than the oxygen gas concentration,
Excess hydrogen gas remains even after the oxygen gas is completely reacted by the catalyst 1. In this case, since the amount of oxygen is small, the flammability limit has not been reached, but surplus hydrogen gas remains.

FIG. 5 shows a method of controlling the supply of the gas containing oxygen in the excess hydrogen gas state. Detecting a hydrogen gas concentration and the oxygen gas concentration in the concentration detector 8 (S1), H ₂ concentration or more than a predetermined amount, H ₂ concentration is determined whether the O ₂ concentration or more (S2,
S3), when those conditions are satisfied, the valve 6 is opened and O ₂ gas is supplied (S4).

For example, only when the hydrogen gas concentration is 4% or higher and the oxygen gas concentration is 3.5% or lower during normal operation, which is very low compared to the hydrogen gas concentration, the valve provided in the gas supply pipe 4 6 is opened, and oxygen gas (may be air) is gradually injected from the nozzle 5 into the storage container 3 from the air conditioning system of the storage container. As a result, the oxygen gas injected into the storage container 3 can be surely reacted with the hydrogen gas by the catalyst 1 without being diffused into the storage container 11. By supplying the gas containing oxygen from the valve 6 provided in the gas supply pipe 4 until the hydrogen gas concentration reaches a sufficiently low level (for example, 4% or less), the surplus hydrogen gas is efficiently processed using the catalyst 1. it can.

By the way, in the catalyst 1, water vapor is generated by the reaction of hydrogen gas and oxygen gas, and the concentration of the combustible gas in the storage container 11 is reduced. However, since the vapor partial pressure in the containment vessel 11 increases, the containment vessel pressure is reduced by the heat exchanger outside the containment vessel. In the present embodiment, in order to accelerate the pressure reduction and to settle the accident, the outlet of the combustible gas concentration reduction device 3 of the dry well 12 and the external heat exchanger 30.
The inlet piping parts of are facing each other.

FIG. 6 is a conceptual diagram for explaining the arrangement and operation of the heat exchanger and the combustible gas concentration reducing device outside the containment vessel. The storage container 3 of the apparatus 100 for reducing the concentration of combustible gas is arranged such that the outlet portion thereof faces the inlet pipe 31 of the heat exchanger 30. Further, the inlet pipe 31 has a jet pump shape. As a result, the ascending flow generated at the outlet of the catalyst 1 by the reaction heat of the hydrogen gas and the oxygen gas is used to
The gas in the storage container 11 around the inlet of the
It can be led to the heat exchanger 30.

In the heat exchanger 30, steam is condensed in the heat transfer tubes due to the temperature difference between the heat exchanger 30 and the cooling water pool 34. Heat exchanger 3
At the bottom header of No. 0, the condensed water and the non-condensable gas such as nitrogen gas are separated, and the condensed water is supplied from the pipe 33 to the reactor pressure vessel 1
0, etc., and the non-condensable gas is discharged from the pipe 32 to the wet well 13. As described above, by disposing the combustible gas concentration reducing device 100 so as to face the inlet pipe section of the condensing heat exchanger 30, the amount of gas flowing into the condensing heat exchanger 30 can be increased, and thus the heat exchanger can be increased. The condensation heat transfer performance of 30 is also improved, and the reduction of the pressure of the containment vessel 11 due to the reduction of the vapor volume can be promoted.

[Embodiment 2] The apparatus for reducing the concentration of combustible gas according to Embodiment 2 is another alternative mainly corresponding to the first object.

FIG. 7 is a schematic configuration diagram of the combustible gas concentration reducing apparatus according to this embodiment. In the combustible gas concentration reduction device 200, the hydrogen gas absorber 9 is arranged below the catalyst 1 in the storage container 3 and, like the catalyst 1, is fixed by the support structure 2. The difference from Embodiment 1 (FIG. 1) described above is that a hydrogen gas absorber 9 is provided instead of the oxygen gas supply means.

As the hydrogen gas absorber 9, it is preferable to use a hydrogen storage metal such as Mg or a Mg—Ni alloy, which has a high storage capacity and a high dissociation temperature for releasing the absorbed hydrogen gas again. In this example, the hydrogen gas absorber 9 is formed into a plurality of plates like the catalyst 1, and the combustible gas flows through the gaps between the plates.

Since the gas heat at the outlet of the catalyst 1 rises due to the reaction heat of the hydrogen gas and the oxygen gas in the catalyst 1, the absorber 9 is used to prevent the hydrogen gas from dissociating due to the temperature rise. Install it below. Further, since the circulation flow passing through the storage container 3 is induced in the storage container 11 by being induced by the reaction heat of the hydrogen gas and the oxygen gas in the catalyst 1, the hydrogen gas absorber 9 is arranged in the storage container 3. Since the hydrogen gas can be selectively absorbed by preliminarily setting the hydrogen gas concentration, the hydrogen gas concentration can be easily reduced.

If a large amount of hydrogen gas generated at the time of severe accident is dealt with only by the hydrogen gas absorber 9, the hydrogen storage capacity of Mg is 7.6% by weight, and therefore, about 1%.
1800 kg of Mg is required. Although it is possible to disperse about 11800 kg of the hydrogen gas absorber 9 in the storage container 11, the amount of the hydrogen gas absorber 9 increases.
Therefore, by using the hydrogen gas absorber 9 and the catalyst 1 together as in the present embodiment, the physical quantity of the hydrogen gas absorber 9 can be significantly reduced. Moreover, since it has no control mechanism, maintenance becomes easy.

FIG. 8 shows a schematic configuration of a combustible gas concentration reducing device according to an alternative of this embodiment. The combustible gas concentration reducing apparatus 300 of this example is a combination of the combustible gas concentration reducing apparatus shown in FIG. 1 and the hydrogen gas absorber 9 (thus, it is also an alternative to the first embodiment).

When compared with the apparatus 100 for reducing the concentration of combustible gas in FIG. 1, the concentration of the excess hydrogen gas in the storage container 11 can be easily reduced by the absorber 9, so that the oxygen gas necessary for treating the excess hydrogen gas is required. The amount of supply can be reduced. FIG.
When compared with the combustible gas concentration reducing device 200 of No. 2, the amount of the hydrogen gas absorber 9 can be reduced.

[Third Embodiment] A combustible gas concentration reducing apparatus according to the third embodiment mainly corresponds to the second object. Hereinafter, an example of the combustible gas concentration reducing device 300 (FIG. 8) having a combination of the oxygen gas supply means and the hydrogen gas absorber 9 will be described, but the device 100 of FIG. 1 or the device 200 of FIG. Good.

FIG. 9 shows a schematic configuration of the combustible gas concentration reducing apparatus of this embodiment. Combustible gas concentration reduction device 30
0, in addition to the configuration of FIG. 8, the storage container 3 is provided with a storage container inlet plate 50 and a storage container outlet plate 51. Entrance plate 50
The outlet plate 51 is formed in a door shape, and is fixed to a position shown by a dotted line with a specific substance (not shown) during normal operation, and the inside of the storage container 3 is isolated from the storage container 11.

When an accident occurs, the temperature and pressure of the storage container 11 rise. As the gas temperature in the storage container 11 rises, a specific substance (for example, a substance having a low melting point such as rubber) that has fixed the inlet plate 50 and the outlet plate 51 is melted, so that the inlet plate 50 and the inlet plate 50 are separated by gravity. The outlet plate 51 rotates to the position shown by the solid line, and the atmosphere of the storage container 11 and the storage container 3
The inside communicates. When using the pressure increase,
It is possible to connect the atmosphere of the storage container 11 and the inside of the storage container 3 by composing the inlet plate 50 and the outlet plate 51 with a rupture disc.

As described above, the entrance and exit of the storage container 3 which is in the closed state during the normal operation is provided with a mechanism for detecting an increase in the temperature or pressure in the storage container at the time of an accident and opening it. It is possible to prevent such substances from adhering to the surface of the catalyst 1 and prevent functional deterioration of the catalyst 1 that acts at the time of an accident.
This improves the reliability of the combustible gas concentration reducing device.

[Embodiment 4] The combustible gas concentration reducing apparatus of Embodiment 3 mainly corresponds to the second object, and is equipped with a test facility for catalyst function. In the following, the flammable gas concentration reducing device shown in FIG. 9 will be described as an example, but it is also applicable to the other embodiments described above (FIGS. 1, 7, and 8).

FIG. 10 shows a schematic configuration of the combustible gas concentration reducing apparatus of this embodiment. In this example, below the catalyst 1 and above the hydrogen gas absorber 9, an inspection gas cylinder 52 containing hydrogen and oxygen whose concentrations are known, a pipe 53, and an inspection gas supply facility including a valve 54, Catalyst 1
A hydrogen gas concentration detector 55, a pipe 57, and a valve 56 are provided at the outlet of the upper storage container 3.

The storage device 3 shown in the drawing shows a state in which the nuclear power plant is under regular inspection, and the inlet and outlet of the storage container 3 are closed by an inlet plate 50 and an outlet plate 51. In order to test the function of the catalyst 1, a test gas having a known combustible gas concentration is introduced from below the catalyst 1, and the hydrogen gas concentration after passing through the catalyst 1 and reacting with oxygen is detected by the detector 55. To detect. Since the reaction efficiency of the catalyst 1 can be evaluated by comparing the hydrogen gas concentration detected by the detector 55 provided inside the sealed storage container 3 with the concentration of the inspected gas that has been introduced, The inspection and inspection of the catalyst 1 becomes easy.

As described above, at the time of periodic inspection, etc., the inspection gas having a known gas concentration is supplied from below the catalyst 1 and the hydrogen gas concentration at the outlet of the catalyst 1 is detected,
The reaction efficiency of the catalyst 1 can be evaluated, and the inspection and inspection of the catalyst 1 becomes easy. This improves the reliability of the combustible gas concentration reducing device.

[0051]

According to the combustible gas concentration reducing apparatus of the present invention, by disposing the hydrogen gas absorber below the catalyst, the hydrogen gas is selectively absorbed by utilizing the circulating flow generated in the catalyst. Therefore, the hydrogen gas concentration can be easily reduced.
Further, since the structure is simple, there is an effect that maintenance is easy.

According to the combustible gas concentration reducing apparatus of the present invention, when excess hydrogen gas remains in the reactor containment vessel due to a severe accident, oxygen gas is injected into the catalyst accommodation vessel to generate excess hydrogen gas. Since the excess hydrogen gas can be reduced by reliably reacting the oxygen gas, the safety of the nuclear reactor is improved. In addition, the concentration of combustible gas (hydrogen, oxygen) in the containment vessel is detected, and the supply of oxygen gas is controlled according to the hydrogen gas amount and the concentration ratio of hydrogen and oxygen. There is an effect that can be removed. Further, since the air in the containment vessel air conditioning system is used as the oxygen gas to be supplied, the configuration is simple and no power source is required.

Further, since the oxygen absorber is arranged below the catalyst in the storage container and oxygen gas is injected into the storage container, the amount of hydrogen gas absorber required for removing the surplus hydrogen gas can be reduced and the cost can be reduced. It will be possible.

According to the combustible gas concentration reducing apparatus of the present invention, since the inlet / outlet portion of the storage container is closed during normal operation, it is possible to prevent dust and the like from adhering to the catalyst surface and deteriorate the catalytic function. You can prevent what you do.

According to the apparatus for reducing the concentration of combustible gas of the present invention, since it is equipped with the means for inspecting the catalyst function used during the regular inspection, the reaction efficiency of the oxidation catalyst can be evaluated, and the inspection and inspection of the catalyst can be performed. This facilitates and improves the reliability of the combustible gas concentration reducing device.

According to the present invention, by disposing the combustible gas concentration reducing device above the storage container space where hydrogen gas is likely to collect, the processing efficiency of the combustible gas is improved.

According to the present invention, the steam discharged from the combustible gas concentration reducing device can be efficiently condensed by the heat exchanger, and the pressure reduction of the containment vessel at the time of an accident can be promoted.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a combustible gas concentration reducing device according to a first embodiment of the present invention.

FIG. 2 is a schematic system diagram of a conventional flammable gas concentration control system.

FIG. 3 is a characteristic diagram showing the relationship between the composition of hydrogen and oxygen and the flammability limit.

FIG. 4 is a layout view of a flammable gas concentration reducing device in a reactor containment vessel.

FIG. 5 is a flowchart showing an oxygen gas supply control method of the combustible gas concentration reducing device.

FIG. 6 is a conceptual diagram showing a pressure reducing action by a combustible gas concentration reducing device and an external heat exchanger.

FIG. 7 is a schematic configuration diagram of a combustible gas concentration reducing device according to a second embodiment of the present invention.

FIG. 8 is a schematic configuration diagram of a combustible gas concentration reducing device according to an alternative of the first or second embodiment of the present invention.

FIG. 9 is a schematic configuration diagram of a combustible gas concentration reducing device according to a third embodiment of the present invention.

FIG. 10 is a schematic configuration diagram of a combustible gas concentration reducing device according to a fifth embodiment of the present invention.

[Explanation of symbols]

1 ... Catalyst, 2 ... Support structure, 3 ... Storage container, 4 ... Piping,
5 ... Nozzle, 6 ... Valve, 7 ... Piping, 8 ... Concentration detector, 9 ...
Hydrogen gas absorber, 10 ... Reactor pressure vessel, 11 ... Reactor containment vessel, 12 ... Dry well, 13 ... Wet well, 15 ... Blower, 16 ... Heater, 17 ... Recombiner, 1
8 ... Cooler, 19 ... Separator, 20, 21 ... Isolation valve,
22 ... Blower, 23, 24 ... Piping, 30 ... Condensing heat exchanger, 31, 32, 33 ... Piping, 34 ... Cooling water pool, 5
0 ... Storage container inlet plate, 51 ... Storage container outlet plate, 52 ... Inspection gas cylinder, 53, 57 ... Piping, 54, 56 ... Valve,
55 ... Concentration detector.

Claims (9)

[Claims] 1. A combustible gas concentration reducing apparatus comprising a catalyst for reacting hydrogen gas and oxygen gas, and a storage container storing the catalyst, wherein a plurality of flammable gas concentration reducing devices are arranged in a reactor containment vessel. A combustible gas concentration reduction device, characterized in that a hydrogen gas absorber is arranged below the catalyst. 2. A combustible gas concentration reducing apparatus comprising a catalyst for reacting hydrogen gas and oxygen gas, and a container for accommodating the catalyst, wherein a plurality of combustible gas concentration reducing devices are arranged in the reactor containment vessel. An oxygen gas supply means for supplying a gas containing oxygen and a concentration detection means for detecting the concentration of the combustible gas (hydrogen and oxygen) in the storage container, and oxygen based on the detected gas concentration A combustible gas concentration reducing device characterized by controlling gas supply. 3. The combustible gas concentration reducing device according to claim 2, wherein a hydrogen gas absorber is arranged below the catalyst in the storage container. 4. The oxygen gas supply means according to claim 2, wherein the oxygen gas supply means is connected to an air conditioning system of a reactor containment vessel, and air is supplied as the gas containing oxygen. Combustible gas concentration reduction device. 5. The inspection gas supply means for supplying a combustible gas (hydrogen and oxygen) having a known concentration to a position below the catalyst, and an inspection gas supply device to a position above the catalyst according to any one of claims 1 to 4. A combustible gas concentration reducing apparatus comprising a hydrogen gas concentration detecting means and enabling a functional test of the catalyst. 6. The reactor containment vessel according to claim 1, wherein an inlet plate is provided at a lower inlet portion of the storage container, and an outlet plate is provided at an upper outlet portion thereof in a closed state during normal operation. A combustible gas concentration reducing device, characterized in that the inlet plate and the outlet plate are opened according to a rise in temperature or pressure at the time of an accident. 7. The combustible gas concentration reducing device according to claim 1, wherein the combustible gas concentration reducing device is arranged more in a space above the space of the reactor containment vessel. . 8. The combustible gas concentration reducing device according to claim 1, wherein the combustible gas concentration reducing device is provided at a position above a space portion of the reactor containment vessel, and an outlet portion of the accommodating device is provided in the reactor containment vessel. A combustible gas concentration reducing device, which is arranged so as to face an inlet pipe portion of a heat exchanger in a cooling water pool installed outside. 9. A method for controlling a combustible gas concentration reducing apparatus, comprising a plurality of catalysts for reacting hydrogen gas and oxygen gas, and a storage container for storing the catalyst, the control method comprising: When it is detected that the hydrogen gas concentration in the container is 4% or more and the oxygen gas concentration is less than or equal to the hydrogen gas concentration, oxygen gas is supplied into the storage container to reduce the flammable gas concentration. Device control method.