JPH1194992A - Catalyst type recombiner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently process burnable gas by providing an iodine filter at the positions upstream of the catalyst inside a chimney wherein burnable gas flows. SOLUTION: Catalyst 1 is supported at the sides of a chimney 2 and the chimney 2 body is placed on a structure wall in the containment with support members 8. The chimney inlet 3 and the chimney outlet 4 are opened and burnable gas contained in the atmosphere in the containment can flow in from below the catalyst 1. Inside the chimney 2, an iodine filter 5 is provided upstream of the catalyst 1. For the iodine filter 5, an equivalent of charcoal filter used in an emergency gas processing system of conventional boiling water reactors, for example is used. By this, iodine being the cause of degrading the performance of catalyst 1 is captured with the iodine filter 5 and simultaneously mixing in the reactor containment is promoted to effectively reduce the burnable gas concentration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalytic recombiner for recombining flammable gas generated at the time of an accident in a nuclear reactor plant by using a catalyst. It relates to a suitable catalytic recombiner.

[0002]

2. Description of the Related Art In a reactor plant, for example, a conventional boiling water reactor, when a coolant loss accident assumed in design occurs, a portable recombination device is transported to a reactor building. Carry in and install. FIG. 2 shows a schematic system diagram of a combustible gas concentration control system using a portable recombining device.
The system configuration includes a blower 15, a heater 16, a thermal reaction type recombiner 17, a cooler 18, a separator 19, piping valves, and a measurement control device.

In the event of a coolant loss accident, the following flammable gas is assumed to be generated. First, the reactor pressure vessel 1
When the fuel temperature within 0 rises, zirconium and water in the fuel cladding react with each other to generate hydrogen gas. In addition, radioactive substances released from the pipe breakage flow into the pressure suppression pool, and hydrogen gas and oxygen gas are generated by radiolysis of water.

[0004] When the concentrations of hydrogen gas and oxygen gas increase in the containment vessel 11 and reach a flammable limit (hydrogen gas concentration of 4% or more and oxygen gas concentration of 5% or more), spontaneous ignition occurs. As a result, the possibility that the integrity of the reactor containment vessel 11 is impaired increases. For this reason, in the conventional flammable gas concentration control system, 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 heated by the recombiner 17 through the heater 16. Recombined by reaction. The steam generated by the recombination reaction is supplied to the cooler 1
After being condensed in 8, water is removed by the separator 19,
The remaining gas is returned to the wet well 13 which is a gas phase space of the suppression chamber.

Further, as a method of reducing the concentration of combustible gas at the time of an accident, Proceedings of the 2nd ASME / JSME Nu
clear Engineering Joint Conference (ICONE2) Vol.
1 (1993), pages 435-438, etc., there is an example in which a catalytic recombiner for recombining a combustible gas with a catalyst such as palladium is installed in a reactor containment vessel. In the case of this catalytic recombiner, the catalyst is housed in the chimney communicating with the space inside the reactor containment vessel. The combustible gas flowing into the chimney reacts on the catalyst to form steam. Further, the natural convection induced by the reaction heat of the combustible gas is formed, thereby promoting the mixing of the atmospheric gas in the containment vessel.

[0006] For this reason, the blower, heater, cooler and the like used in the conventional portable recombination device become unnecessary. Further, since piping and valves for guiding the combustible gas to the outside of the containment vessel can be omitted, simplification of equipment and improvement in maintainability can be expected.

[0007]

In the event of a coolant loss accident, the fission products present in the reactor coolant and the fission products released from the fuel rods are released to the reactor containment vessel. It is assumed in the design. Of the fission products released into the gas phase in the reactor containment, iodine is thought to adhere to the catalyst by the flow formed in the reactor containment by the catalytic recombiner, The reaction of the combustible gas on the catalyst may be alienated.

[0008] Further, even when an oil fire or a cable fire occurs, there is a possibility that the performance of the catalyst may be deteriorated due to the adhesion of oil and soot to the catalyst. In addition, in the event of a coolant loss accident, the steam inside the reactor containment vessel is condensed,
Since the containment spray for removing iodine floating in the gas phase operates, water droplets and the like are also floating in the atmosphere in the reactor containment vessel. If a large amount of moisture that flows in with the combustible gas adheres to the catalyst, the catalyst temperature decreases, and thus the activation time of the catalyst may be delayed until the attached moisture evaporates. However, in the above documents, the effects of reaction inhibitors such as iodine, oil and soot, and the effects of water droplets and the like were not clearly described.

An object of the present invention is to use a circulating flow formed by the heat of reaction of a combustible gas to capture or remove substances which are considered to suppress the reaction in the catalyst on the upstream side of the catalyst. An object of the present invention is to provide a catalytic recombiner for efficiently treating combustible gas.

[0010]

The object of the present invention is to provide a catalyst for causing a recombination reaction of combustible gas generated in the event of a nuclear reactor plant accident, and a chimney for accommodating the catalyst.
In a large number of catalytic recombiners located inside the reactor containment vessel, install an iodine filter, a particle filter, and a moisture removal device at a position upstream of the catalyst inside the chimney through which pre-flammable gas flows. Can be achieved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment corresponding to the object of the present invention will be described with reference to FIGS.

FIG. 1 shows a schematic diagram of a catalytic recombiner in a first embodiment. In this embodiment, the catalyst 1 using platinum or palladium is formed into a plurality of plates and housed inside the chimney 2. The catalyst 1 is supported on the side surface of the chimney 2, and the chimney 2 itself is installed on a structural wall in the containment vessel by a support member 8.
The chimney inlet 3 and the chimney outlet 4 are open, and have a structure in which flammable gas contained in the atmosphere in the containment vessel can flow in from below the catalyst 1. An iodine filter 5 is provided inside the chimney 2 and upstream of the catalyst 1. As the elementary filter 5, for example, a filter equivalent to a charcoal filter used in an emergency gas treatment system of a conventional boiling water reactor is used.

When an accident occurs, the concentration of flammable gas increases in the containment vessel and flows into the chimney 2 together with steam and nitrogen gas. The combustible gas passes through the iodine filter 5 and reaches the catalyst 1, but iodine contained in the mixed gas is captured by the iodine filter 5. Due to the reaction heat on the catalyst 1, the gas temperature at the upper end of the catalyst 1 is about 300 ° C.
As a result, the density difference from the mixed gas outside the chimney 2 increases, and a circulating flow in the containment vessel is formed by buoyancy. The flow induced by this heat of reaction is
This has the same effect as installing a blower in the containment vessel, and has the effect of actively sucking the gas around the chimney 2. Accordingly, iodine, which is one of the factors that degrade the performance of the catalyst 1, is captured by the iodine filter 5, and at the same time, the mixing in the reactor containment vessel is promoted to effectively reduce the flammable gas concentration.

FIG. 3 shows a structure in which the chimney 2 can be divided by the area of the catalyst 1 and the iodine filter 5 in the first embodiment. The chimney 2 can be divided and assembled by hooks and screws. By forming such a chimney 2 in a divided structure, inspection and replacement work of the catalyst 1 and the iodine filter 5 can be easily performed.

FIG. 4 shows a second embodiment of the present invention. The difference from the first embodiment shown in FIG. 1 is that a particle filter 6 is provided upstream of the iodine filter 5. By installing the particle filter 6, even if a fire occurs in the containment vessel, particles such as oil and soot can be easily adsorbed. The chemical form of iodine released into the containment vessel includes particulate CsI. Most of the particulate CsI is removed by containment spray, but some of it may float in the reactor containment. For this reason, the particle filter 6 can capture not only particles such as oil and soot but also suspended particulate CsI, thereby preventing the iodine filter 5 from being clogged.
It is possible to prevent the performance of the catalyst 1 from deteriorating more than the embodiment.

FIG. 5 shows a third embodiment of the present invention. The difference from the second embodiment is that the inlet of the chimney 2 is a horizontal duct, and a moisture separator 7 is provided near the chimney inlet 3 and upstream of the particle filter 6 and the iodine filter 5. It is that you are. The moisture separating device 7 includes a chimney 2
Since water droplets such as spray water contained in the mixed gas flowing into the catalyst are removed, adhesion of water droplets to the catalyst 1 is prevented. In addition, since the moisture separator 7 is installed vertically in a horizontal duct near the chimney inlet, even if water droplets adhere, they flow down due to gravity, so that the water droplets can be efficiently removed. . Furthermore, since the performance of the iodine filter 5 is not sufficiently exhibited when the humidity is high, the performance of the iodine filter 5 can be improved by installing the moisture separating device 7 on the upstream side of the iodine filter 5. Also contributes.

It is considered that such an iodine filter 5, a particle filter 6, and a moisture separator 7 can be used as those substantially equivalent to those used in the above-mentioned emergency gas processing system. Further, the pressure loss of these filters is small (about 0.05 kg / cm ^{2 in the} conventional emergency gas processing system as a whole), and the influence on the flow rate of the circulating flow induced by the heat of reaction is small.

FIG. 6 shows a dispersed arrangement of the catalytic recombiner of the present invention in a reactor containment vessel 11 of a boiling water reactor.
In this embodiment, in the area of the dry well 12, it is installed near the biological shielding wall 29 surrounding the reactor pressure vessel 10, and in the wet well 13, a catalytic recombiner is installed near the inner wall 30 of the suppression chamber. Are distributed. In addition, even when the containment vessel spray is activated, the distance between the spray headers 27 and 28 arranged near the wall of the containment vessel 11 should be increased in order to reduce the possibility that the spray water scatters on the catalyst 1. I have to.

Thus, inside the chimney 2,
By providing a filter at a position upstream of the catalyst 1 for capturing and removing a substance that degrades the catalytic performance, the function of treating a flammable gas at the time of an accident can be favorably maintained. Also, as in the case of the coolant loss accident,
Even if an event that iodine is released inside is assumed, the iodine filter 5 built in the chimney 2 efficiently captures iodine by a blower action utilizing the reaction heat of the catalytic recombiner. Can be adsorbed.

As a result, the amount of leakage of iodine from the reactor containment vessel 11 to the reactor building is reduced. Therefore, even when air in the reactor building is processed through the emergency gas processing system, the Exposure to the area around the plant site will be further reduced, contributing to improved safety of the reactor plant.

Although the embodiments of the present invention have been described for a boiling water reactor, the catalytic recombiner of the present invention can be similarly applied to a pressurized water reactor and the like.

[0022]

According to the first aspect of the present invention, iodine is located at a position upstream of the catalyst in a chimney that contains a catalyst for causing a recombination reaction of combustible gas generated at the time of an accident in a nuclear reactor plant. By installing the filter, it is possible to prevent a decrease in catalyst performance. In addition, iodine released into the gas phase of the containment vessel can be captured and adsorbed by the catalytic recombiner with an iodine filter, so the amount of iodine leaking from the containment vessel to the reactor building And the amount of exposure around the site of the nuclear reactor plant is further reduced. According to the second aspect of the present invention, in addition to the effects of the first aspect, by installing a particle filter on the upstream side of the iodine filter, when a fire occurs in the reactor containment vessel, In addition to adsorbing oil and soot and the like, it also traps particulate CsI, thereby preventing clogging of the iodine filter 5 and more effectively preventing deterioration in catalyst performance.

According to the third aspect of the present invention, in addition to the effects of the first or second aspect of the present invention, by installing a moisture separator upstream of the iodine filter, the inside of the reactor containment vessel can be improved. In addition to efficiently removing water droplets contained in the atmospheric gas, the start of the catalyst is not delayed, and the performance of the iodine filter is improved.

According to the fourth aspect of the present invention, since the chimney has a structure that can be divided in the region of the catalyst and the filter, inspection and replacement of the catalyst and the filters can be easily performed.

[Brief description of the drawings]

FIG. 1 is a schematic view of a catalytic recombiner according to a first embodiment of the present invention.

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

FIG. 3 is a schematic diagram showing a case where a chimney is divided in the first embodiment.

FIG. 4 is a schematic view of a catalytic recombiner according to a second embodiment of the present invention.

FIG. 5 is a sectional view of a catalytic recombiner according to a third embodiment of the present invention.

FIG. 6 is a cross-sectional view when the catalytic recombiner of the present invention is disposed in a containment vessel.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Catalyst, 2 ... Chimney, 3 ... Chimney inlet, 4 ... Chimney outlet, 5 ... Iodine filter, 6 ... Particle filter, 7
... Moisture separator, 8 ... Support member, 10 ... Reactor pressure vessel, 11 ... Reactor containment vessel, 12 ... Dry well, 13
... wet well, 14 ... suppression pool, 15 ... blower, 16 ... heater, 17 ... recombiner, 18 ... cooler, 1
9 ... separator, 20, 21 ... isolation valve, 22, 23, 2
4 ... Valve, 25 ... Pump, 26 ... Heat exchanger, 27, 28 ...
Spray header, 29: living body shielding wall, 30: pressure suppression indoor wall.

Claims (4)

[Claims] 1. A catalytic recombiner comprising a catalyst for recombining flammable gas generated in an accident of a nuclear reactor plant and a chimney for accommodating the catalyst and arranged in a large number in a reactor containment vessel. 3. The catalytic recombiner according to claim 1, wherein an iodine filter is installed at a position upstream of the catalyst inside the chimney through which the combustible gas flows. 2. The catalytic recombiner according to claim 1, wherein a particle filter is provided upstream of said iodine filter. 3. The catalytic recombiner according to claim 1, wherein a moisture separator is provided upstream of the iodine filter. 4. The catalytic recombiner according to claim 1, wherein said chimney is divided into a catalyst and a filter region.