JP6624584B2 - Recombination device - Google Patents

Description

  The present invention relates to a recombination device for bonding hydrogen and oxygen using a catalyst.

  In a radioactive waste storage tank storing a high level of radioactive waste, it is conceivable that hydrogen is generated in the radioactive waste storage tank by radioactive decomposition of water. If the internal hydrogen concentration increases with time and reaches the explosion limit, a hydrogen explosion may occur in the storage tank. When a hydrogen explosion occurs in a radioactive waste storage tank, the function of confining radioactive materials is lost, and radioactive materials may be released to the outside.

  In order to prevent such a hydrogen explosion, there is a need for a means for reducing the hydrogen concentration so that the hydrogen concentration in the radioactive waste storage tank does not reach the explosion limit.

  Conventionally, as a countermeasure against a severe accident in a nuclear power plant, a device has been known in which a large amount of hydrogen generated by a zirconium-water reaction is recombined with oxygen using a catalyst to reduce the hydrogen concentration (Patent) Reference 1).

JP 2011-174773 A

  However, existing recombination devices developed as a countermeasure for severe accidents are installed inside the reactor containment vessel or reactor building, and are not compatible with installation in radioactive waste storage tanks. That is, the existing recombination device cannot be installed in a facility such as a radioactive waste storage tank where the internal space area is narrow and airtightness is required.

  In addition, in containers and tanks other than radioactive waste storage tanks where hydrogen is generated inside and the hydrogen concentration may increase over time, the hydrogen concentration is reduced before the hydrogen concentration reaches the explosion limit. We need some means to make it happen.

  However, such containers and tanks usually do not have a large internal space such as a reactor containment vessel, and are required to be airtight. For this reason, it is difficult or impossible to install a large-scale reconnection device already developed as a measure against severe accidents.

  The present invention has been made in view of the above-described problems of the related art, and has a small internal space area such as a radioactive waste storage tank and a catalyst suitable for installation in equipment requiring airtightness. It is an object of the present invention to provide a recombination device of the type.

  In order to solve the above-mentioned problem, the present invention according to a first aspect is a recombination device attached to a container to combine hydrogen generated inside the container with oxygen using a catalyst, wherein A first cylindrical body through which the gas containing hydrogen and oxygen flows, and connected to an outlet of the first cylindrical body, the gas flowing from the first cylindrical body is filled with the gas. And a return section for returning to the container, wherein the first cylindrical body has a catalyst section on the inlet side for binding the hydrogen and the oxygen.

  The present invention according to a second aspect is the invention according to the first aspect, wherein the return portion is formed so as to surround an outer surface of the first cylindrical body, It is characterized by having a direction change part connected to one cylindrical body and changing the direction of the gas flowing from the first cylindrical body and flowing out the gas to the second cylindrical body.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the first tubular body and the return portion are configured to be integrally detachable from the container. It is characterized by.

  The present invention according to a fourth aspect is characterized in that the first cylindrical body and / or the return portion include an opening sealing member that hermetically seals an opening formed in the container. And

  According to a fifth aspect of the present invention, in the present invention according to any one of the first to fourth aspects, the catalyst section has a large number of through holes carrying the catalyst on a surface thereof, and includes the hydrogen and the oxygen. It is characterized by having a substantially plate-like or tubular member for introducing the gas to be treated and recombining the hydrogen and the oxygen.

  The present invention according to a sixth aspect is the invention according to any one of the first to fifth aspects, wherein the catalyst portion is formed by separating through holes adjacent to each other with thin walls. And

  The present invention according to a seventh aspect is the invention according to the sixth aspect, wherein a cross section of the catalyst part is polygonal.

  According to an eighth aspect of the present invention, in the invention according to the sixth or seventh aspect, the plurality of through holes are formed by buoyancy of a gas caused by heat generated by a recombination reaction between the hydrogen and the oxygen in the catalyst section. The effective length of the first cylindrical body and the thickness of the catalyst portion are set such that natural convection occurs in the first cylindrical body against the flow resistance in the holes. Features.

  The invention according to a ninth aspect is the invention according to the eighth aspect, wherein the thickness of the catalyst part is about 5 mm.

  ADVANTAGE OF THE INVENTION According to this invention, the space area | regions, such as a radioactive waste storage tank, are narrow, and the catalyst-type recombination apparatus suitable for installation in the facilities which require airtightness can be provided.

FIG. 2 is a front view showing the catalytic recombination device according to the first embodiment of the present invention mounted on a radioactive waste storage tank. FIG. 2 is a top view of the recombination device shown in FIG. 1. FIG. 2 is a longitudinal sectional view of the recombination device shown in FIG. 1. FIG. 4 is an arrow view along the line IV-IV in FIG. 1. FIG. 6 is an arrow view along the line VV in FIG. 5. FIG. 2 is a top view illustrating a catalyst holder of the recombination apparatus illustrated in FIG. 1. FIG. 7 is a longitudinal sectional view of the catalyst holder shown in FIG. 6. FIG. 7 is a bottom view of the catalyst holder shown in FIG. 6. FIGS. 2A and 2B are diagrams for explaining the structure of a catalyst unit of the recombination apparatus shown in FIG. 1, wherein FIG. 1A is a plan view schematically showing the catalyst unit, and FIG. . 9A is an enlarged plan view of a portion Xa in FIG. 9A, and FIG. 9B is a longitudinal sectional view showing an enlarged portion Xb of FIG. 9B. FIG. 4 is an enlarged longitudinal sectional view of a part XI in FIG. 3. 4 is a graph showing the relationship between the thickness of a catalyst unit and the amount of hydrogen treatment. FIG. 2 is a schematic diagram illustrating a flow path configuration model of the recombination apparatus illustrated in FIG. 1. 2 is a graph showing an optimum range of the recombination device shown in FIG. 1.

  Hereinafter, a catalytic recombination device according to an embodiment of the present invention will be described with reference to the drawings.

  The recombination device according to the present embodiment is a device for combining hydrogen and oxygen using a catalyst, and is particularly suitable for installation in a radioactive waste storage tank. In particular, it is suitable for mounting on a nozzle provided in a radioactive waste storage tank.

  However, the recombination device according to the present invention can be installed not only in the radioactive waste storage tank but also in a container or a tank in which hydrogen is generated inside and the hydrogen concentration may increase with time.

  As shown in FIGS. 1 and 3, a cylindrical nozzle 51 is provided at the upper part of the radioactive waste storage tank 50, and the recombination device 1 according to the present embodiment is detachably attached to the nozzle 51. It is installed.

  As shown in FIGS. 1 and 3, the recombination apparatus 1 according to the present embodiment has a first cylindrical body 2 through which a gas to be treated including hydrogen and oxygen flows. The first cylindrical body 2 is formed of a cylindrical member. However, the member forming the first cylindrical body 2 is not limited to a cylindrical member, and for example, a cylindrical member having a square cross section can be used.

  As shown in FIGS. 1 to 4, the flow direction of the gas flowing out of the first cylindrical body 2 is changed at the outlet of the first cylindrical body 2 and returned to the radioactive waste storage tank again. A return section is provided. Specifically, the return portion includes a second cylindrical member 4 formed so as to surround the outer surface of the first cylindrical member 2 and a head plate (return member) connected to an upper portion of the second cylindrical member. Part) 3 (shape of a bowl), the gas flowing out from the upper part of the first cylindrical body spreads in the radial direction in the direction changing part of the end plate part, and spreads vertically upward from vertically downward. The flow direction is changed to flow downward in the flow path between the first tubular body and the second tubular body, and returned to the radioactive waste storage tank again. The second cylindrical body 4 has a flange portion 5 formed at a lower end.

  The flange portion 5 of the second cylindrical body 4 is fixed to the flange portion 52 formed at the upper end of the nozzle 51 of the radioactive waste storage tank 50 with bolts 6. An airtight seal is formed between the flange portions 5 and 52, thereby ensuring airtightness inside the radioactive waste storage tank 50.

  As shown in FIGS. 3 and 4, the inner peripheral surface of the second cylindrical body 4 and the outer peripheral surface of the first cylindrical body 2 are formed in an elongated plate shape arranged at 90 ° intervals in the circumferential direction. They are connected by an internal connecting member 7.

  As shown in FIG. 1, the upper half of the first cylindrical body 2 is disposed inside the nozzle 51 of the radioactive waste storage tank 50, and the inner peripheral surface of the nozzle 51 and the second cylindrical body 4. An annular gas flow path 8 is formed between the first cylindrical body 2 and the outer peripheral surface of the first cylindrical body 2. The gas that has flowed upward from the upper end opening of the first cylindrical body 2 changes its flow downward in the flow direction changing part (return part) 3 and returns to the radioactive waste storage tank 50 through the annular flow path 8. I do.

  As shown in FIGS. 1 and 3, a dome in which the end plate portion 4 </ b> A of the second cylindrical body 4, that is, the portion facing the outlet of the first cylindrical body 2 is inclined downward from the center toward the outside. It is formed in a shape.

  As shown in FIGS. 1 and 3, a catalyst structure 9 is provided on the inlet side (lower end side) of the first cylindrical body 2. The catalyst structure 9 has the catalyst holder 10 shown in FIGS. 6 to 8 and the substantially disk-shaped or substantially cylindrical catalyst part 11 shown in FIG.

The catalyst section 11 is formed by filling a gas passage with a small-diameter pebble carrying a catalyst on the surface, or arranging a plate carrying the catalyst on the surface, or a large number of honeycombs carrying the catalyst on the surface. -Shaped wall surfaces are arranged.
The catalyst holder 10 is formed of a substantially annular frame-shaped holding member that holds a peripheral portion of the catalyst portion 11, and the substantially disk-shaped or substantially cylindrical catalyst portion 11 is fitted into a concave portion of the catalyst holder 10. The catalyst holder can be formed of, for example, a stainless steel material.

  Hereinafter, a catalyst unit having a honeycomb structure that is likely to be small and high in performance and a structure related thereto will be described.

  A large number of through holes (flow paths) provided in the catalyst section 11 have a polygonal shape such as a triangle, a quadrangle, a pentagon, or a hexagon in cross section, and flow paths adjacent to each other are partitioned by thin walls. (Honeycomb structure). The catalyst section uses porous ceramics, stainless steel, or the like as a support. That is, a large number of through holes 12 are formed in the catalyst section 11 as shown in FIG. The through-hole 12 extends along the direction of introduction of the gas to be treated into the first tubular body 2 (in this example, the axial direction of the first tubular body 2), and the inside thereof is treated. The target gas (including hydrogen and oxygen) flows.

  The catalyst is provided at least on the inner peripheral surface of each through hole 12 in the catalyst portion. By adopting the honeycomb structure, the specific surface area (surface area per unit volume) of the catalyst section 11 can be increased, so that the contact efficiency between the gas to be treated and the catalyst can be greatly increased.

  FIG. 11 shows a mounting structure of the catalyst structure 9 to the first tubular body 2. An annular projection 13 is formed on the inner peripheral surface of the first cylindrical body 2. Below the annular protrusion 13, a short cylindrical support member 15 having an annular support portion 14 formed at the upper end is disposed. The peripheral portion of the catalyst structure 9 is arranged between the annular protrusion 13 and the annular support portion 14. The short tubular support member 15 is fixed to the first tubular body 2 with bolts 16, and the catalyst structure 9 is fixed to the tubular portion 2.

  Next, the recombination action of hydrogen and oxygen in the recombination device 1 according to the present embodiment will be described.

  The recombination device 1 according to the present embodiment does not require a power source when used, and utilizes natural convection in the first cylindrical body 2 as a driving force. That is, the buoyancy of the gas caused by the heat generated by the recombination reaction of hydrogen and oxygen in the catalyst structure 9 prevents the flow resistance in the plurality of through holes 12 of the catalyst portion 11 from flowing through the first cylindrical body 2. The effective length of the first cylindrical body 2 (the length of a portion contributing to the generation of natural convection) and the thickness of the catalyst portion 11 are set so that natural convection occurs.

  That is, the gas to be treated containing high-concentration hydrogen generated in the radioactive waste storage tank 50 and accumulated in the upper part of the storage tank flows from the lower end inlet of the first cylindrical body 2 and passes through the catalyst structure 9. Then, water vapor is generated by a recombination reaction between hydrogen and oxygen. In the presence of a catalyst, the recombination reaction occurs even at room temperature. The gas is heated by the heat generated by the recombination reaction to generate buoyancy due to the density difference, and natural convection is generated using the buoyancy as a driving force (chimney effect).

  The treated gas containing water vapor generated by the recombination reaction is discharged upward from the upper end opening of the first cylindrical body 2. The released gas changes its flow downward and returns to the radioactive waste storage tank 50 through the annular flow path 8.

  FIG. 12 shows the relationship between the catalyst height (height of the catalyst section 11) and the amount of hydrogen treatment in the case of a hydrogen concentration of 4 vol%, a reaction rate of 100%, and natural convection. The hydrogen treatment amount indicates a treatment amount (kg / h) per unit inflow area of the gas to be treated into the recombination device 1.

  As can be seen from FIG. 12, as the catalyst height (height of the catalyst portion 11) increases, the hydrogen treatment amount decreases. Since the reaction between hydrogen and oxygen is very fast, the reaction is substantially completed immediately after the gas to be treated is introduced into the catalyst unit 11. Therefore, even if the height of the catalyst is increased, there is almost no contribution to the promotion of the reaction. Rather, since the flow resistance in the catalyst unit 11 increases, the flow rate of the gas to be treated decreases, and as a result, the amount of hydrogen treatment decreases.

  Therefore, even if the height of the catalyst section is larger than 5 mm, the hydrogen processing capacity is reduced, while the size of the recombination device is increased, whereas if the height of the catalyst section is smaller than 5 mm, the hydrogen processing capacity is reduced. It can be seen that the size of the recombination device is improved and the size of the recombination device is reduced.

  Next, a desirable range (dimensions of main parts) as the recombination device in the present embodiment will be examined.

  FIG. 13 shows a flow path configuration model of the recombination apparatus 1 according to the present embodiment.

  The buoyancy caused by the heat generated by the catalytic reaction between hydrogen and oxygen is expressed by the following equation (1) when the flow is in a laminar flow region.

P _A = Δρ × g × h ₂ (1)
here,
P _A : Buoyancy [N / m ² ] due to heat generated by catalytic reaction
Δρ: density difference ρ _IN −ρ _OUT [kg / m ³ ]
ρ _IN : Inlet gas density [kg / m ³ ]
ρ _OUT : Outlet gas density [kg / m ³ ]
g: Gravitational acceleration [m / s ² ]
h _2: chimney height [m]
Note that the chimney height is an effective height corresponding to a portion where the chimney effect occurs inside the tubular portion 2.

  The flow resistance in the catalyst section 11 is represented by the following equation (2).

_{P B = 32 × μ × h} 1 × V IN / d 1 2 ···· (2)
here,
P _B : Flow resistance [N / m ² ]
μ: viscosity coefficient [Pa · s]
h ₁ : catalyst height [m]
V _IN : Inlet flow rate [m / s]
d ₁ : equivalent diameter of catalyst channel [m]
Assuming that the buoyancy P _A due to heat generated by the catalyst and the flow resistance P _B in the catalyst section 11 are balanced (P _A = P _B ), the following is obtained from the equations (1) and (2).

_{h 2 / h 1 = 32 ×} μ × V IN / d 1 2 / (Δρ × g) ···· (3)
Further, if H = h ₁ + h ₂ , the following is obtained.

_{H / h 1 = 32 × μ} × V IN / d 1 2 / (Δρ × g) +1 ··· (4)
FIG. 14 shows a desirable range (black portion in the graph) for the recombination device 1 according to the present embodiment based on the equation (4).

In FIG. 14, 300 mm for the size reduction of the recombination device the upper limit of H, due to the 3mm from limitations in manufacturing the lower limit of _{h 1,} in FIG. 14, H / _{h 1,} for the upper limit is 100, the lower limit is , H = h ₁ (h ₂ = 0 mm). In addition, the lower limit of _VIN is set to 0.3 m / s in consideration of the hydrogen throughput of the existing recombination device. The upper limit of d ₁ has a 1.79mm based on manufacturable catalyst unit.

  As described above, according to the catalytic recombination device 1 of the present embodiment, the return portion 3 is provided at the outlet of the first cylindrical body 2 provided with the catalyst structure 9, and the return Since the opening of the nozzle 51 of the waste storage tank 50 is hermetically sealed, even in the radioactive waste storage tank 50 where the internal space area is narrow and airtightness is required, the recombination device 1 can be attached without any trouble. .

  By attaching the recombination device 1 to the radioactive waste storage tank 50 in this manner, the concentration of hydrogen generated inside the radioactive waste storage tank 50 is controlled to prevent the explosion limit from being reached, and the occurrence of a hydrogen explosion Possibilities can be excluded. In the recombining apparatus 1 according to the present embodiment, in order to ensure a reliable natural circulation force, the temperature of the gas between the first cylindrical body 2 and the second cylindrical body 4 is maintained at a low temperature. If necessary, the second cylindrical body 4 is forcibly cooled by providing a cooling fan (independent of the recombining device, not shown) around the second cylindrical body 4 as necessary. However, even if such a cooling mechanism is provided, the radioactive waste storage tank including the recombination device can have an airtight structure, and the cooling mechanism is also simple, so it is very simple compared to the conventional one. Hydrogen explosion can be prevented by a simple recombination device.

  Further, the recombination apparatus 1 according to the present embodiment can be mounted on the existing nozzle 51 provided on the upper part of the radioactive waste storage tank 50, so that a special structure for installing the recombination apparatus 1 is required. In addition, labor and cost for installation work can be reduced.

  In addition, the recombination apparatus 1 according to the present embodiment uses a catalyst unit in which a large number of through holes 12 are formed along the direction in which the gas to be treated is introduced into the first cylindrical body 2 as the catalyst unit 11. As a result, the natural convection due to the Chimney effect can be ensured, and the amount of hydrogen treatment per unit volume of the catalyst can be greatly increased as compared with the conventional recombination device.

  As a result, the size of the catalyst structure 9 including the catalyst portion 11 can be significantly reduced as compared with the case of a conventional catalytic recombining device. This makes it possible to reduce the size and weight of the entire device. Even if a cooling fan is required, the installation and removal of the device can be facilitated independently of the need for a cooling fan due to the reduction in size and weight of the reconnection device 1, and the exposure of workers due to shortening of the operation time is reduced. Can also be reduced.

  Further, according to the recombination device 1 according to the present embodiment, since the catalyst structure 9 is detachably mounted inside the first tubular body 2, the catalyst structure 9 is removed from the first tubular body 2. By removing the catalyst, the catalyst can be easily replaced.

  Further, according to the recombination device 1 according to the present embodiment, the end plate portion 4A of the second cylindrical body 4, that is, the portion facing the outlet of the first cylindrical body 2 is directed downward from the center toward the outside. Since the water vapor is cooled by the end plate portion 4A of the second cylindrical body 4 and condensed water adheres to the surface of the end plate portion 4A, the condensed water is formed on the surface of the end plate portion 4A in the radial direction. It flows outward. Therefore, it is possible to prevent the condensed water from dropping into the upper end opening of the first cylindrical body 2 and prevent the water from adhering to the catalyst and hindering the basic reaction.

DESCRIPTION OF SYMBOLS 1 Catalytic recombination device 2 Cylindrical part 3 Return part (opening sealing member, end plate, flow direction change part)
Reference Signs List 4 Second cylindrical body 4A End plate part of second cylindrical body 5 Flange part 6 Bolt 7 Internal connecting member 8 Annular flow path 9 Catalyst structure 10 Catalyst holder 11 Catalyst part 12 Through hole of catalyst part 13 Annular projection Part 14 Annular support part 15 Short cylindrical support member 16 Bolt 50 Radioactive waste storage tank 51 Nozzle 52 Flange part

Claims (8)

A recombination device attached to a container to combine hydrogen generated inside the container with oxygen using a catalyst,
A first cylindrical body through which the gas containing the hydrogen and the oxygen flowing from the container flows,
A return portion connected to an outlet of the first cylindrical body and returning gas flowing out of the first cylindrical body to the container,
Said first tubular body, have a catalyst unit for coupling the hydrogen and the oxygen to the inlet side,
The return portion is a second tubular body formed to surround the outer surface of the first tubular body, and is connected to the first tubular body and flows out of the first tubular body. A direction changing unit that changes the direction of the gas and flows into the second cylindrical body,
The recombination device , wherein the second tubular body is attached to the container . It said first cylindrical body and the back portion is configured so as to be removably attached to the container as a unit, the recombination device according to claim 1. The recombination device according to claim 2, wherein the first cylindrical body and / or the return portion includes an opening sealing member that hermetically seals an opening formed in the container. The catalyst section has a large number of through-holes carrying the catalyst on its surface, and has a substantially plate-like or cylindrical member that introduces the gas containing the hydrogen and the oxygen and recombines the hydrogen and the oxygen. The recombination device according to any one of claims 1 to 3 . The recombination device according to any one of claims 1 to 4 , wherein the catalyst portion is formed by separating through holes adjacent to each other with a thin wall. The recombination device according to claim 5 , wherein a cross section of the catalyst unit is a polygon. Due to the buoyancy of the gas caused by the heat generated by the recombination reaction between the hydrogen and the oxygen in the catalyst section, natural convection occurs in the first cylindrical body against the flow resistance in the plurality of through holes. as the effective length and thickness of the catalyst portion of the first tubular member is set, the recombination device according to claim 5 or 6. The recombination device according to claim 7 , wherein the thickness of the catalyst part is about 5 mm or less.