US20020196890A1 - Dry radioactive substance storage facility - Google Patents
Dry radioactive substance storage facility Download PDFInfo
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- US20020196890A1 US20020196890A1 US09/961,299 US96129901A US2002196890A1 US 20020196890 A1 US20020196890 A1 US 20020196890A1 US 96129901 A US96129901 A US 96129901A US 2002196890 A1 US2002196890 A1 US 2002196890A1
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C19/00—Arrangements for treating, for handling, or for facilitating the handling of, fuel or other materials which are used within the reactor, e.g. within its pressure vessel
- G21C19/02—Details of handling arrangements
- G21C19/06—Magazines for holding fuel elements or control elements
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
Definitions
- the present invention relates to a dry radioactive substance storage facility and, more particularly, to a radioactive substance storage facility for storing radioactive substance including high-level radioactive wastes and radioactive substance produced in nuclear power plants.
- a dry radioactive substance storage facility stores vitrified radioactive wastes and aggregate of radioactive substance while cooling the same by air that flows around the same. Dry radioactive substance storage facilities are disclosed in Japanese Patent Laid-open Nos. Hei 5-273392 and Hei 8-43591.
- the dry radioactive substance storage facility disclosed in Japanese Patent Laid-open No. Hei 5-273392 has a concrete building having partition walls of a radiation shielding substance and defining a storage room. Many storage tubes are placed in the storage room and aggregates of radioactive substance are contained in the storage tubes. Decay heat generated by the radioactive substance contained in the storage tubes is dissipated into cooling air for cooling. The cooling air flows horizontally through spaces between the storage tubes in a cooling air passage between the ceiling slab and the floor slab of the storage room.
- the storage facility disclosed in Japanese Patent Laid-open No. Hei 8-43591 relates to a shielding structure.
- the dry radioactive substance storage facility disclosed in Japanese Patent Laid-open No. Hei 8-43591 is characterized by the use of a heat-resistant resin for forming a structure for enclosing radioactive substance therein.
- the dry radioactive substance storage facility disclosed in Japanese Patent Laid-open No. Hei 5-273392 has walls capable of shielding radioactive rays emitted by radioactive substance. However, nothing is mentioned in Japanese Patent Laid-open No. Hei 5-273392 about the improvement of radiation shielding ability.
- the present invention provides a dry radioactive substance storage facility comprising a plurality of first radiation shielding members disposed in a storage room on the side of an air inlet duct through which air is supplied into the storage room, a plurality of second radiation shielding members disposed in the storage room on the side of an stack through which air is discharged outside, in which first air passages are formed between the first radiation shielding members, and second air passages are formed between the second radiation shielding members.
- the air inlet duct can be shielded from radioactive rays by the first radiation shielding members, and the stack can be shielded from radioactive rays by the second radiation shielding members. Accordingly, the amount of radiation reaching the outside through the air inlet duct and the stack is attenuate greatly, whereby the radiation shielding performance of the dry radioactive substance storage facility is improved. Since air flows through spaces between the first and the second radiation shielding members, there is no possibility that the ability to cool the radioactive substance contained in the storage tubes is attenuate significantly.
- the first and the second radiation shielding members are arranged in a plurality of rows in the flowing direction of air, the first radiation shielding members in the row on the upstream side with respect to the flow of air are disposed opposite to spaces between the first radiation shielding members in the row on the downstream side with respect to the flow of air, and the second radiation shielding members in the row on the downstream side with respect to the flow of air are disposed opposite to spaces between the second radiation shielding members in the row on the upstream side with respect to the flow of air.
- the first radiation shielding members in the row on the upstream side are disposed opposite to spaces between the first radiation shielding members in the row on the downstream side, the first radiation shielding members on the upstream side are able to intercept radiation through the spaces toward the air inlet duct. Since the second radiation shielding members in the row on the downstream side are disposed opposite to spaces between the second radiation shielding members in the row on the upstream side, the second radiation shielding members on the downstream side are able to intercept radiation propagating through the spaces toward the stack.
- the dry radioactive substance storage facility has a further improved radiation shielding ability.
- the first radiation shielding members are thermally connected to storage tubes on the upstream side of the storage tubes
- the second radiation shielding members are thermally connected to the storage tubes on the downstream side of the storage tubes. Since the radiation shielding members are thermally connected to the storage tubes, the radiation shielding members are cooled by air. Consequently, the reduction of cooling ability due to the partial covering of the storage tubes with the radiation shielding members can be avoided.
- a plurality of first baffling members are disposed on the side of the air inlet duct in the storage room
- a plurality of second baffling members are disposed on the side of the stack in the storage room
- each of the first and the second baffling members comprises a neutron shielding member and a gamma ray shielding member.
- the first baffling members exercise the same function as the first radiation shielding members
- the second baffling members exercise the same function as the second radiation shielding members.
- the first and the second baffling members are capable of shielding neutrons and gamma rays.
- the first and the second baffling members are formed by covering a neutron shielding member with a gamma ray shielding member. Since the neutron shielding member is covered with the gamma ray shielding member, the gamma ray shielding member can easily be attached to the neutron shielding member.
- upper ones of the plurality of the second baffling members overlap more deeply and are dislocated more greatly toward the stack. Since upper ones of the plurality of the second baffling members overlap more deeply and are dislocated more greatly toward the stack, radiation propagating toward the stack are intercepted by the second baffling members, which enhances the effect of shielding radiation propagating toward the stack.
- the first baffling members are disposed in an inclined position so as to guide air supplied through the air inlet duct toward an upper region of the storage room. Since the first baffling members are disposed in an inclined position so as to guide air supplied through the air inlet duct toward an upper region of the storage room, the first baffling members utilizes a radiation attenuating function and a radiation reflecting function for shielding radiation. Consequently, the amount of radiation propagating toward the air inlet duct can greatly be attenuate. Part of radiation propagating toward the first baffling members is attenuated as the same permeates the first baffling members, and part of radiation is reflected downward by the inclined first baffling members. Consequently, the amount of radiation propagating toward the air inlet duct can greatly be attenuate.
- radiation scattering members are disposed in the storage room on the side of the air inlet duct relative to the first radiation shielding members, and on the side of the stack relative to the second radiation shielding members.
- the radiation scattering members scatters radiation propagated through the spaces between the adjacent baffling members to attenuate the amount of radiation propagating toward the air inlet duct and the stack.
- each of the radiation scattering members comprises a neutron shielding member and a gamma ray shielding member.
- the radiation scattering member is formed by covering the neutron shielding member with the gamma ray shielding member.
- a surface of the radiation scattering member facing the fuel storage room has a shape to reflect radiation downward.
- FIG. 1 is a longitudinal sectional view of a dry radioactive substance storage facility in a preferred embodiment according to the present invention
- FIG. 2 is a cross-sectional view of a storage room for storing radioactive substance in the radioactive substance storage facility of FIG. 1;
- FIG. 3 is a cross-sectional view of a radiation shielding member
- FIG. 4 is a cross-sectional view of a storage room in a dry radioactive substance storage facility in a second embodiment according to the present invention.
- FIG. 5 is a diagram showing the dependence of surface increase in temperature in storage tubes and radiation attenuation ratio on the thickness of a radiation shielding member
- FIG. 6 is a cross-sectional view of a storage room in a dry radioactive substance storage facility in a third embodiment according to the present invention.
- FIG. 7 is a cross-sectional view of a storage room in a dry radioactive substance storage facility in a fourth embodiment according to the present invention.
- FIG. 8 is a cross-sectional view of a storage room in a dry radioactive substance storage facility in a fifth embodiment according to the present invention.
- FIG. 9 is a cross-sectional view of a storage room in a dry radioactive substance storage facility in a sixth embodiment according to the present invention.
- FIG. 10 is a sectional view of a dry radioactive substance storage facility in a seventh embodiment according to the present invention.
- FIG. 11 is a sectional view of baffling plates included in the dry radioactive substance storage facility of FIG. 10;
- FIG. 12 is a fragmentary sectional view of a radiation scattering member included in the dry radioactive substance storage facility of FIG. 10;
- FIG. 13 is a fragmentary, longitudinal sectional view of an air inlet duct and associated parts in the radioactive substance storage facility of FIG. 10;
- FIG. 14 is a fragmentary sectional view of a modification of the radiation scattering member.
- a dry radioactive substance storage facility removes decay heat generated by radioactive substance stored therein by air flow. Therefore, the dry radioactive substance storage facility needs openings that serve as an air inlet and an air outlet. The greater the openings or the straighter an air passage for air flow, the less flow resistance against air flow and the higher the efficiency of cooling the radioactive substance stored in a storage room. On the other hand, the greater the openings or the straighter an air passage, the less the radiation shielding ability of the dry radioactive substance storage facility. The dry radioactive substance storage facility must be satisfactory in both cooling performance and radiation shielding performance.
- the inventors of the present invention made studies to cope with both cooling performance and radiation shielding performance and found that both cooling performance and radiation shielding performance can be coped with by disposing radiation shielding members on the inlet and the outlet side of an air passage in the storage room. Dry radioactive substance storage facilities based on findings obtained by studies will be described hereinafter.
- a dry radioactive substance storage facility 1 in a first embodiment according to the present invention stores spent fuel assemblies, i.e., radioactive substance produced in nuclear power plants.
- the dry radioactive substance storage facility 1 has a building of reinforced concrete construction having a fuel storage room 3 .
- the fuel storage room extends between a ceiling slab 10 and a floor slab 11 .
- Many storage tubes 2 are arranged in the storage room 3 extending under the ceiling slab 10 .
- An air inlet duct 8 has an opening 8 A opening into the storage room 3 .
- An stack 9 has an opening 9 A opening into the storage room 3 .
- a plurality of radiation shielding members 6 a are disposed on the side of the air inlet duct 8 in the storage room 3 .
- a plurality of radiation shielding members 6 b are disposed on the side of the stack 9 in the storage room 3 .
- the radiation shielding members 6 a and 6 b are round rods.
- the storage tubes 2 are disposed between the radiation shielding members 6 a and the radiation shielding members 6 b in the storage room 3 .
- the air inlet duct 8 has an air inlet 4 opening outside.
- the stack 9 has an air outlet 5 opening outside.
- the spent fuel assemblies transported from a nuclear power plant to the dry radioactive substance storage facility 1 are handled in a fuel handling room 20 to put the same into the storage tubes 2 .
- the spent fuel assemblies are stored temporarily in the storage tubes 2 .
- Outside air taken through the air inlet 4 into the air inlet duct 8 flows in air flow 7 through the air inlet duct 8 and spaces between the radiation shielding members 6 a into spaces between the storage tubes 2 .
- the air flow 7 flowing through the spaces between the storage tubes 2 cools the storage tubes 2 to remove decay heat generated by the spent fuel assemblies contained in the storage tubes 2 .
- the air heated by the decay heat flows through spaces between the radiation shielding members 6 b and the stack 9 and is discharged outside through the air outlet 5 .
- the amount of radiation propagating toward the opening of the air passage in the amount of radiation emitted by the spent fuel assemblies contained in the storage tubes 2 is the sum of the amount of radiation propagated directly from the storage tubes 2 and the amount of radiation propagated through the spaces between the radiation shielding members.
- the ratio between those amounts is dependent on the ratio between a solid angle defined by the opening and the storage tube 2 and a solid angle defined by the radiation shielding member taking into consideration of the transmittance of the radiation shielding members. Accordingly, the amount of radiation that propagates toward the opening can be attenuate by reducing the amount of radiation that passes the spaces between the radiation shielding members or by reducing the solid angle defined by the opening and the storage tube.
- the radiation shielding members 6 a are arranged in two rows on the side of the air inlet duct, and the radiation shielding members 6 b are arranged in two rows on the side of the stack.
- the radiation shielding members 6 a and 6 b are arranged in a triangular array arrangement; that is, the radiation shielding members 6 a and 6 b are arranged on the vertices of equilateral triangles.
- the radiation shielding members 6 a in the upstream row are disposed so as to cover spaces between the radiation shielding members 6 a in the downstream row.
- the radiation shielding members 6 b in the downstream row are disposed so as to cover spaces between the radiation shielding members 6 b in the upstream row.
- the amount of radiation by the spent fuel assemblies stored in the storage room 3 and propagates toward the openings 8 A and 9 A can greatly be attenuate and, consequently, the amount of radiation that propagates through the air inlet 4 and the air outlet 5 outside the dry radioactive substance storage facility 1 can greatly be attenuate.
- the radiation shielding members 6 a and 6 b disposed on the upstream and the downstream side of the storage tubes 2 increase resistance against air flow.
- the increment of the resistance can be limited to a small value by forming the radiation shielding members 6 a and 6 b in the same cross-sectional shape as the storage tubes 2 . Consequently, the amount of radiation that propagates toward the openings 8 A and 9 A can greatly be attenuate without involving significant reduction in air-cooling performance.
- Expression (1) represents the relation between the thickness a of the radiation shielding members, i.e., the size along the direction of propagation of radiation, and the amount of radiation transmitting the radiation shielding members. ⁇ ⁇ 0 ⁇ exp ⁇ [ - ⁇ a ⁇ ( E ) ⁇ a ] ( 1 )
- a is the thickness of the radiation shielding members along the direction of propagation of radiation
- ⁇ a (E) is the absorption coefficient of the radiation shielding members with radiation having energy E
- ⁇ 0 is the amount of radiation before transmitting the radiation shielding members
- ⁇ is the amount of radiation transmitting the radiation shielding members.
- Expression (1) It is known from Expression (1) that the greater radiation shielding members have higher radiation shielding ability.
- the thickness of the radiation shielding members necessary to secure the least necessary radiation shielding ability can be determined by using Expression (1).
- the upstream side surfaces of the radiation shielding members 6 a and 6 b employed in this embodiment are curved so that the level of resistance exerted by the radiation shielding members 6 a and 6 b against the air flow is low and pressure loss in the air passage is low. Forming the downstream side surfaces of the radiation shielding members 6 a and 6 b in a curved surface is also effective in reducing pressure loss in the air passage.
- a radiation shielding member 6 in a modification has the shape of a round tube.
- the wall thickness a of the radiation shielding member 6 is a thickness necessary to secure necessary radiation shielding effect determined by using Expression (1).
- the radiation shielding ability of the radiation shielding member 6 having the shape of a round tube is equivalent to that of the radiation shielding members having the shape of a rod.
- a radioactive substance storage facility 1 A in a second embodiment according to the present invention will be described with reference to FIG. 4.
- radiation shielding members 6 a are attached to the upstream side surfaces of storage tubes 2
- radiation shielding members 6 b are attached to the downstream side surfaces of the storage tubes 2 .
- the storage tubes 2 combined with the radiation shielding members 6 a are arranged in two rows adjacent to an opening 8 A
- the storage tubes 2 combined with the radiation shielding members 6 b are arranged in two rows adjacent to an opening 9 A.
- the second embodiment similarly to the first embodiment shown in FIG. 1, is capable of greatly reducing the amount of radiation that reaches the openings 8 A and 8 B.
- ⁇ is increase in temperature
- ⁇ is the thickness of the radiation shielding member
- ⁇ is the thermal conductivity of the radiation shielding member
- the radiation shielding ability and the heat removing ability of the storage tube 2 combined with the radiation shielding member were calculated by using Expressions (1) and (2), in which it was assumed that the energy of radiation is 1 MeV and the radiation shielding member is made of iron. Calculated values are shown in FIG. 5. It is known from FIG. 5 that the radiation attenuation ratio is about 1/100 when the thickness of the radiation shielding member is 10 cm and gamma rays of 1 MeV in energy is radiated. Heat generated by the spent fuel assemblies is transmitted through the storage tube 2 to the radiation shielding member. Increase in temperature of the surface of the storage tube 2 is about 0.1° when the heat flux across the radiation shielding member is 100 W/m, and is about 1° when 1 kW/m. Therefore, increase in temperature of the storage tube 2 is small and the reduction of the heat removing ability of the storage tube 2 is small when the energy of radiation or heat flux is on the level as mentioned above.
- the second embodiment has the following effects. Since the radiation shielding members of the second row are joined to the storage tubes to eliminate spaces between them, the storage room 3 can be formed in a short length, i.e., a size along the direction of flow of air.
- a dry radioactive substance storage facility 1 B in a third embodiment according to the present invention will be described with reference to FIG. 6.
- storage tubes 2 are arranged in lines and rows in a storage room 3 .
- Radiation shielding members 6 a are arranged in a single row on the side of an opening 8 A so as to correspond directly to the adjacent storage tubes 2 , respectively.
- Radiation shielding members 6 b are arranged in a single row on the side of an opening 9 A so as to correspond directly to the adjacent storage tubes 2 , respectively.
- the radioactive substance storage facility 1 B in the third embodiment differs from the radioactive substance storage facility 1 in the first embodiment in the arrangement of the storage tubes 2 .
- the dry radioactive substance storage facility in the third embodiment attenuates the amount of radiation reaching the openings 8 A and 9 A by the radiation shielding members 6 a and 6 b more effectively than the conventional dry radioactive substance storage facility, the amount of radiation reaching the openings 8 A and 9 A in the dry radioactive substance storage facility 1 B in the third embodiment is greater than that in the dry radioactive substance storage facility 1 in the first embodiment.
- a dry radioactive substance storage facility 1 C in a fourth embodiment according to the present invention will be described with reference to FIG. 7.
- storage tubes 2 are arranged, similarly to those of the dry radioactive substance storage facility 1 B, in lines and rows.
- Radiation shielding members 6 a on the side of an opening 8 A are arranged in two rows in a triangular array arrangement.
- Radiation shielding members 6 b on the side of an opening 9 A are arranged in two rows in a triangular array arrangement.
- the dry radioactive substance storage facility 1 C is the same in effect as the dry radioactive substance storage facility 1 .
- a dry radioactive substance storage facility 1 D in a fifth embodiment according to the present invention will be described with reference to FIG. 8.
- Radiation shielding members 6 a and 6 b are arranged in two rows in a triangular array arrangement in a storage room 3 of the dry radioactive substance storage facility 1 D.
- the radiation shielding members 6 a and 6 b have an oval cross section elongated in the direction of air flow 7 .
- the dry radioactive substance storage facility 7 D is the same in effect as the dry radioactive substance storage facility 1 .
- the radiation shielding members 6 a and 6 b in the fifth embodiment elongated in the direction of air flow 7 have increased radiation attenuating effect. Therefore, the amount of radiation reaching the openings 8 A and 9 A in the dry radioactive substance storage facility 1 D is less than that in the dry radioactive substance storage facility 1 .
- a dry radioactive substance storage facility 1 E in a sixth embodiment according to the present invention will be described with reference to FIG. 9.
- Storage tubes 2 are arranged in a storage room 3 of the dry radioactive substance storage facility 1 E in an arrangement similar to that of the storage tubes 2 of the dry radioactive substance storage facility 1 A.
- Radiation shielding members 6 a similarly to those of the dry radioactive substance storage facility 1 A shown in FIG. 4, are attached to the upstream side surfaces of the storage tubes 2 in two rows adjacent to an opening 8 A.
- Radiation shielding members 6 b similarly to those of the dry radioactive substance storage facility 1 A, are attached to the downstream side surfaces of the storage tubes 2 in two rows adjacent to an opening 9 A.
- the radiation shielding members 6 a and 6 b have a wedge-shaped cross section.
- the dry radioactive substance storage facility 1 E is the same in effect as the dry radioactive substance storage facility 1 A. Since the radiation shielding members have a wedge-shaped cross section, the radiation shielding members 6 a are disposed with their edges directed in a direction opposite the direction of air flow 7 and the radiation shielding members 6 b are disposed with their edges direction in the direction of air flow 7 , the radiation shielding members 6 a and 6 b exert less resistance against the air flow 7 .
- a dry radioactive substance storage facility 1 F in a seventh embodiment according to the present invention will be described with reference to FIG. 10.
- the dry radioactive substance storage facility 1 F has a building of reinforced concrete institution having a fuel storage room 3 . Only matters relating to the dry radioactive substance storage facility 1 F different from those of the dry radioactive substance storage facility 1 will be described.
- a plurality of baffling plates 6 d are arranged in the storage room 3 near an air inlet duct.
- a plurality of baffling plates 6 d are arranged in the storage room 3 near an stack.
- Radiation scattering member 21 A is disposed on the side of the air inlet duct with respect to the baffling plates 6 c and is attached to a side wall of the storage room 3 , facing the baffling plates 6 c.
- Radiation scattering member 21 B is disposed on the side of the stack with respect to the baffling plates 6 d and is attached to a side wall of the storage room 3 , facing the baffling plates 6 d.
- each of the baffling plates 6 c and 6 d is formed by covering a neutron shielding member 12 with a gamma ray shielding member 13 .
- the neutron shielding member 12 is made of a stainless steel containing a neutron absorbing substance, such as boron.
- the stainless steel containing boron is strong and is suitable for forming the structural member of the baffling plate.
- the neutron shielding member 12 may be formed of a substance containing iron, such as a carbon steel.
- the gamma ray shielding member 13 may be formed of a hydrogen compound, such as a hydrocarbon.
- the baffling plates 6 c and 6 d are arranged vertically so as to overlap each other between the ceiling slab 10 and the floor slab 11 . Some of the baffling plates 6 d are arranged so that upper ones are shifted toward the stack relative to the lower ones. The baffling plates 6 c are inclined upward toward the storage tubes 2 .
- the radiation scattering member 21 B similarly to the baffling plates 6 c and 6 d, is formed by covering a neutron shielding member 12 with a gamma ray shielding member 13 .
- the radiation scattering member 21 A is the same in construction as the radiation scattering member 21 B.
- Each of the radiation scattering members 21 A and 21 B has inclined surfaces 14 facing obliquely downward and horizontal surfaces 15 facing upward on its side facing the baffling plates.
- the inclined surfaces 14 and the horizontal surfaces 15 form a sawtoothed side surface.
- Air supplied through the air inlet duct 8 flows through spaces between the baffling plates 6 c into spaces between the storage tubes 2 disposed in the storage room 3 .
- the air flowing through the spaces between the storage tubes 2 cools the storage tubes 2 and remove decay heat generated by the spent fuel assemblies contained in the storage tubes 2
- the air heated by decay heat flows through spaces between the baffling plates 6 d and the stack 9 and is discharged outside.
- the baffling plates 6 c and 6 d formed by combining the neutron shielding member 12 and the gamma ray shielding member 13 are capable of shielding neutrons and gamma rays.
- the baffling plates 6 c and 6 d has a radiation shielding function to intercept neutrons and gamma rays. Therefore, the baffling plates need not be arranged at small intervals and hence do not cause pressure loss. Therefore, cooling ability to cool the spent fuel assemblies contained in the storage tubes 2 is not attenuate by the baffling plates 6 c and 6 d and radiation can be intercepted efficiently.
- the gamma ray shielding member 13 can be easily fixed to the neutron shielding member 12 .
- the gamma ray shielding member 13 may be attached to the surface to the neutron shielding member 12 via an adhesive.
- the baffling plates 6 c and 6 d correspond to the radiation shielding members 6 a and 6 b used in the dry radioactive substance storage facility 1 , respectively.
- Radioactive rays (neutrons and gamma rays) emitted by the spent fuel assemblies stored in the storage room 3 are intercepted by concrete walls defining the storage room 3 including the ceiling slab 10 and the floor slab 11 . Radiation that propagate toward the stack 9 is intercepted by the baffling plates 6 d.
- the baffling plates 6 d formed by combining the neutron absorbing member and the gamma ray absorbing member are capable of efficiently shielding neutrons and gamma rays. The radiation shielding function of the baffling plates 6 d will be described with reference to FIG.
- the radiation shielding ability of the baffling plate 6 d is expressed by: ⁇ ⁇ 0 ⁇ exp ⁇ [ - 1 ⁇ 2 ⁇ ⁇ ⁇ a ⁇ ( E ) ⁇ a + ⁇ b ⁇ ( E ) ⁇ b ⁇ ] ( 3 )
- b is the thickness of the neutron shielding member 12 of the baffling plate 63 along the path of the radiation 16
- a is the thickness of the gamma ray shielding member 13 along the path of the radiation 16
- ⁇ 0 is the amount of energy of the radiation 16 before transmitting the baffling plate 6 B
- ⁇ is the amount of energy of the radiation 16 transmitting throgh the baffling plate 6 B
- ⁇ b is the absorption coefficient of the neutron shielding member 12 to the radiation 16 having energy E
- ⁇ a is the absorption coefficient of the gamma ray shielding member 13 to the radiation 16 .
- the radiation shielding ability increases with the increase in the thicknesses of the neutron shielding member 12 and the gamma ray shielding member 13 . Since the baffling plates 6 d are arranged vertically so as to overlap each other and some of the baffling plates 6 d are arranged so that upper ones are shifted toward the stack relative to the lower ones, the radiation 16 propagating obliquely upward are intercepted by the plurality of baffling plates 6 d. Accordingly, the radiation (neutrons and gamma rays) propagating toward the stack 9 can efficiently be intercepted.
- the radiation reflected by the inclined baffling plates 6 c does not propagate toward the air inlet duct 8 and propagate downward necessarily.
- the baffling plates 6 c exercise both a radiation attenuating function and a radiation reflecting function, whereby the radiation propagating toward the air inlet duct 8 is attenuate significantly.
- the function of the radiation scattering member 21 B will be explained.
- the radiation 17 propagated through spaces between the baffling plates 6 d is attenuated by the neutron shielding member 12 and the gamma ray shielding member 13 of the radiation scattering member 21 B.
- Part of radiation 19 falling on the inclined surfaces 14 are reflected downward and is attenuated by lower portions of the radiation scattering member 21 B below the inclined surfaces 14 reflecting the radiation 19 or by the floor slab 11 .
- the radiation scattering member 21 B does not reflect the radiation upward, the amount of the radiation propagating toward the stack 9 is further attenuate.
- the radiation scattering member 21 B Since the radiation scattering member 21 B is disposed in an inherently dead space through which air flows scarcely, the radiation scattering member 21 B does not increase pressure loss in the air passage and does not attenuate the ability to cool the spent fuel assemblies. Since the radiation scattering member 21 B is formed by covering the neutron shielding member 12 with the gamma ray shielding member 13 , similarly to the baffling plates, the gamma ray shielding member 13 can simply be attached to the neutron shielding member 12 .
- the radiation scattering member 21 A is the same in function as the radiation scattering member 21 B and attenuates the amount of radiation that propagates toward the air inlet duct 8 .
- a radiation scattering member 21 C in a modification has a surface facing the baffling plates and having the shape of comb teeth.
- the radiation scattering member 21 C is formed, similarly to the radiation scattering members 21 A and 21 B, by covering a neutron shielding member 12 with a gamma ray shielding member 13 .
- the present invention has been described in its preferred embodiments as applied to cooling the storage tubes 2 containing the spent fuel assemblies, the present invention is effectively applicable also to storing vitrified radioactive wastes instead of the spent fuel assemblies.
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Abstract
Description
- The present invention relates to a dry radioactive substance storage facility and, more particularly, to a radioactive substance storage facility for storing radioactive substance including high-level radioactive wastes and radioactive substance produced in nuclear power plants.
- Aggregate of radioactive substance used as fuel assemblies in a nuclear power plant is reprocessed to recover fissionable nuclear fuel substance including uranium and plutonium. High-level radioactive wastes resulting from the reprocessing of radioactive substance are vitrified. Since the vitrification of radioactive wastes generates decay heat, the vitrified radioactive wastes must be stored and cooled until the heat generation rate of the radioactive wastes decreases to an extent that permits disposal. Aggregate of radioactive wastes is kept in a storage pool in the nuclear power plant. The amount of aggregates of radioactive substance increases year by year and, eventually, exceeds the capacity of the storage pool of the nuclear power plant. Therefore, it is desired to construct a new storage facility capable of storing a large amount of aggregate of radioactive substance for a long time.
- A dry radioactive substance storage facility stores vitrified radioactive wastes and aggregate of radioactive substance while cooling the same by air that flows around the same. Dry radioactive substance storage facilities are disclosed in Japanese Patent Laid-open Nos. Hei 5-273392 and Hei 8-43591.
- The dry radioactive substance storage facility disclosed in Japanese Patent Laid-open No. Hei 5-273392 has a concrete building having partition walls of a radiation shielding substance and defining a storage room. Many storage tubes are placed in the storage room and aggregates of radioactive substance are contained in the storage tubes. Decay heat generated by the radioactive substance contained in the storage tubes is dissipated into cooling air for cooling. The cooling air flows horizontally through spaces between the storage tubes in a cooling air passage between the ceiling slab and the floor slab of the storage room.
- The storage facility disclosed in Japanese Patent Laid-open No. Hei 8-43591 relates to a shielding structure.
- The dry radioactive substance storage facility disclosed in Japanese Patent Laid-open No. Hei 8-43591 is characterized by the use of a heat-resistant resin for forming a structure for enclosing radioactive substance therein.
- The dry radioactive substance storage facility disclosed in Japanese Patent Laid-open No. Hei 5-273392 has walls capable of shielding radioactive rays emitted by radioactive substance. However, nothing is mentioned in Japanese Patent Laid-open No. Hei 5-273392 about the improvement of radiation shielding ability.
- In the dry radioactive substance storage facility disclosed in Japanese Patent Laid-open No. Hei 8-43591, some of structural members are formed of a substance capable of shielding radioactive rays. Therefore, the number of structures only for radioactive ray interception can be attenuate. However, nothing is mentioned in Japanese Patent Laid-open No. Hei 8-43591 about cooling ability.
- In those prior art dry radioactive substance storage facilities, structure is discussed only on the basis of examination of cooling structure or shielding ability, and nothing is discussed on the interception of radioactive rays.
- Accordingly, it is an object of the present invention to provide a dry radioactive substance storage facility capable of improving radioactive ray shielding ability without significantly reducing cooling performance.
- With the foregoing object in view, the present invention provides a dry radioactive substance storage facility comprising a plurality of first radiation shielding members disposed in a storage room on the side of an air inlet duct through which air is supplied into the storage room, a plurality of second radiation shielding members disposed in the storage room on the side of an stack through which air is discharged outside, in which first air passages are formed between the first radiation shielding members, and second air passages are formed between the second radiation shielding members.
- The air inlet duct can be shielded from radioactive rays by the first radiation shielding members, and the stack can be shielded from radioactive rays by the second radiation shielding members. Accordingly, the amount of radiation reaching the outside through the air inlet duct and the stack is attenuate greatly, whereby the radiation shielding performance of the dry radioactive substance storage facility is improved. Since air flows through spaces between the first and the second radiation shielding members, there is no possibility that the ability to cool the radioactive substance contained in the storage tubes is attenuate significantly.
- Preferably, the first and the second radiation shielding members are arranged in a plurality of rows in the flowing direction of air, the first radiation shielding members in the row on the upstream side with respect to the flow of air are disposed opposite to spaces between the first radiation shielding members in the row on the downstream side with respect to the flow of air, and the second radiation shielding members in the row on the downstream side with respect to the flow of air are disposed opposite to spaces between the second radiation shielding members in the row on the upstream side with respect to the flow of air.
- Since the first radiation shielding members in the row on the upstream side are disposed opposite to spaces between the first radiation shielding members in the row on the downstream side, the first radiation shielding members on the upstream side are able to intercept radiation through the spaces toward the air inlet duct. Since the second radiation shielding members in the row on the downstream side are disposed opposite to spaces between the second radiation shielding members in the row on the upstream side, the second radiation shielding members on the downstream side are able to intercept radiation propagating through the spaces toward the stack. Thus, the dry radioactive substance storage facility has a further improved radiation shielding ability.
- Preferably, the first radiation shielding members are thermally connected to storage tubes on the upstream side of the storage tubes, and the second radiation shielding members are thermally connected to the storage tubes on the downstream side of the storage tubes. Since the radiation shielding members are thermally connected to the storage tubes, the radiation shielding members are cooled by air. Consequently, the reduction of cooling ability due to the partial covering of the storage tubes with the radiation shielding members can be avoided.
- Preferably, a plurality of first baffling members are disposed on the side of the air inlet duct in the storage room, a plurality of second baffling members are disposed on the side of the stack in the storage room, and each of the first and the second baffling members comprises a neutron shielding member and a gamma ray shielding member. The first baffling members exercise the same function as the first radiation shielding members, and the second baffling members exercise the same function as the second radiation shielding members. The first and the second baffling members are capable of shielding neutrons and gamma rays.
- Preferably, the first and the second baffling members are formed by covering a neutron shielding member with a gamma ray shielding member. Since the neutron shielding member is covered with the gamma ray shielding member, the gamma ray shielding member can easily be attached to the neutron shielding member.
- Preferably, upper ones of the plurality of the second baffling members overlap more deeply and are dislocated more greatly toward the stack. Since upper ones of the plurality of the second baffling members overlap more deeply and are dislocated more greatly toward the stack, radiation propagating toward the stack are intercepted by the second baffling members, which enhances the effect of shielding radiation propagating toward the stack.
- Preferably, the first baffling members are disposed in an inclined position so as to guide air supplied through the air inlet duct toward an upper region of the storage room. Since the first baffling members are disposed in an inclined position so as to guide air supplied through the air inlet duct toward an upper region of the storage room, the first baffling members utilizes a radiation attenuating function and a radiation reflecting function for shielding radiation. Consequently, the amount of radiation propagating toward the air inlet duct can greatly be attenuate. Part of radiation propagating toward the first baffling members is attenuated as the same permeates the first baffling members, and part of radiation is reflected downward by the inclined first baffling members. Consequently, the amount of radiation propagating toward the air inlet duct can greatly be attenuate.
- Preferably, radiation scattering members are disposed in the storage room on the side of the air inlet duct relative to the first radiation shielding members, and on the side of the stack relative to the second radiation shielding members. The radiation scattering members scatters radiation propagated through the spaces between the adjacent baffling members to attenuate the amount of radiation propagating toward the air inlet duct and the stack.
- Preferably, each of the radiation scattering members comprises a neutron shielding member and a gamma ray shielding member. Preferably, the radiation scattering member is formed by covering the neutron shielding member with the gamma ray shielding member. Preferably, a surface of the radiation scattering member facing the fuel storage room has a shape to reflect radiation downward.
- FIG. 1 is a longitudinal sectional view of a dry radioactive substance storage facility in a preferred embodiment according to the present invention;
- FIG. 2 is a cross-sectional view of a storage room for storing radioactive substance in the radioactive substance storage facility of FIG. 1;
- FIG. 3 is a cross-sectional view of a radiation shielding member;
- FIG. 4 is a cross-sectional view of a storage room in a dry radioactive substance storage facility in a second embodiment according to the present invention;
- FIG. 5 is a diagram showing the dependence of surface increase in temperature in storage tubes and radiation attenuation ratio on the thickness of a radiation shielding member;
- FIG. 6 is a cross-sectional view of a storage room in a dry radioactive substance storage facility in a third embodiment according to the present invention;
- FIG. 7 is a cross-sectional view of a storage room in a dry radioactive substance storage facility in a fourth embodiment according to the present invention;
- FIG. 8 is a cross-sectional view of a storage room in a dry radioactive substance storage facility in a fifth embodiment according to the present invention;
- FIG. 9 is a cross-sectional view of a storage room in a dry radioactive substance storage facility in a sixth embodiment according to the present invention;
- FIG. 10 is a sectional view of a dry radioactive substance storage facility in a seventh embodiment according to the present invention;
- FIG. 11 is a sectional view of baffling plates included in the dry radioactive substance storage facility of FIG. 10;
- FIG. 12 is a fragmentary sectional view of a radiation scattering member included in the dry radioactive substance storage facility of FIG. 10;
- FIG. 13 is a fragmentary, longitudinal sectional view of an air inlet duct and associated parts in the radioactive substance storage facility of FIG. 10; and
- FIG. 14 is a fragmentary sectional view of a modification of the radiation scattering member.
- A dry radioactive substance storage facility removes decay heat generated by radioactive substance stored therein by air flow. Therefore, the dry radioactive substance storage facility needs openings that serve as an air inlet and an air outlet. The greater the openings or the straighter an air passage for air flow, the less flow resistance against air flow and the higher the efficiency of cooling the radioactive substance stored in a storage room. On the other hand, the greater the openings or the straighter an air passage, the less the radiation shielding ability of the dry radioactive substance storage facility. The dry radioactive substance storage facility must be satisfactory in both cooling performance and radiation shielding performance. The inventors of the present invention made studies to cope with both cooling performance and radiation shielding performance and found that both cooling performance and radiation shielding performance can be coped with by disposing radiation shielding members on the inlet and the outlet side of an air passage in the storage room. Dry radioactive substance storage facilities based on findings obtained by studies will be described hereinafter.
- Referring to FIG. 1, a dry radioactive substance storage facility1 in a first embodiment according to the present invention stores spent fuel assemblies, i.e., radioactive substance produced in nuclear power plants. The dry radioactive substance storage facility 1 has a building of reinforced concrete construction having a
fuel storage room 3. The fuel storage room extends between aceiling slab 10 and a floor slab 11.Many storage tubes 2 are arranged in thestorage room 3 extending under theceiling slab 10. Anair inlet duct 8 has anopening 8A opening into thestorage room 3. Anstack 9 has anopening 9A opening into thestorage room 3. A plurality ofradiation shielding members 6 a are disposed on the side of theair inlet duct 8 in thestorage room 3. A plurality ofradiation shielding members 6 b are disposed on the side of thestack 9 in thestorage room 3. Theradiation shielding members storage tubes 2 are disposed between theradiation shielding members 6 a and theradiation shielding members 6 b in thestorage room 3. Theair inlet duct 8 has anair inlet 4 opening outside. Thestack 9 has anair outlet 5 opening outside. - The spent fuel assemblies transported from a nuclear power plant to the dry radioactive substance storage facility1 are handled in a
fuel handling room 20 to put the same into thestorage tubes 2. The spent fuel assemblies are stored temporarily in thestorage tubes 2. Outside air taken through theair inlet 4 into theair inlet duct 8 flows inair flow 7 through theair inlet duct 8 and spaces between theradiation shielding members 6 a into spaces between thestorage tubes 2. Theair flow 7 flowing through the spaces between thestorage tubes 2 cools thestorage tubes 2 to remove decay heat generated by the spent fuel assemblies contained in thestorage tubes 2. The air heated by the decay heat flows through spaces between theradiation shielding members 6 b and thestack 9 and is discharged outside through theair outlet 5. - In the dry radioactive substance storage facility1 thus constructed, the amount of radiation propagating toward the opening of the air passage in the amount of radiation emitted by the spent fuel assemblies contained in the
storage tubes 2 is the sum of the amount of radiation propagated directly from thestorage tubes 2 and the amount of radiation propagated through the spaces between the radiation shielding members. The ratio between those amounts is dependent on the ratio between a solid angle defined by the opening and thestorage tube 2 and a solid angle defined by the radiation shielding member taking into consideration of the transmittance of the radiation shielding members. Accordingly, the amount of radiation that propagates toward the opening can be attenuate by reducing the amount of radiation that passes the spaces between the radiation shielding members or by reducing the solid angle defined by the opening and the storage tube. - As shown in FIG. 2, the
radiation shielding members 6 a are arranged in two rows on the side of the air inlet duct, and theradiation shielding members 6 b are arranged in two rows on the side of the stack. Theradiation shielding members radiation shielding members radiation shielding members 6 a in the upstream row are disposed so as to cover spaces between theradiation shielding members 6 a in the downstream row. Theradiation shielding members 6 b in the downstream row are disposed so as to cover spaces between theradiation shielding members 6 b in the upstream row. - Part of radiation emitted by the spent fuel assemblies contained in the
storage tubes 2 and propagating toward theopening 8A is absorbed and attenuated by theradiation shielding members 6 a disposed on the side of thestorage tubes 2, and the rest propagates through the spaces between theradiation shielding members 6 a disposed on the side of thestorage tubes 2 and is attenuated by theradiation shielding members 6 a disposed on the side of theopening 8A. Since the solid angle directly including thestorage tubes 2 as viewed from theopening 8A is small, the amount of radiation that propagates directly toward theopening 8A without being obstructed by theradiation shielding members 6 a can greatly be attenuate. - Part of radiation by the spent fuel assemblies contained in the
storage tubes 2 and propagating toward theopening 9A is absorbed and attenuated by theradiation shielding members 6 b disposed on the side of thestorage tubes 2, and the rest propagates through the spaces between theradiation shielding members 6 b disposed on the side of thestorage tubes 2 and is attenuated by theradiation shielding members 6 b disposed on the side of theopening 9A. Since the solid angle directly including thestorage tubes 2 as viewed from theopening 9A is small, the amount of radiation that propagates directly toward theopening 9A without being obstructed by theradiation shielding members 6 b can greatly be attenuate. - Thus, the amount of radiation by the spent fuel assemblies stored in the
storage room 3 and propagates toward theopenings air inlet 4 and theair outlet 5 outside the dry radioactive substance storage facility 1 can greatly be attenuate. - The
radiation shielding members storage tubes 2 increase resistance against air flow. The increment of the resistance can be limited to a small value by forming theradiation shielding members storage tubes 2. Consequently, the amount of radiation that propagates toward theopenings - The radiation shielding performance of the radiation shielding members shown in FIG. 2 will be explained in connection with Expression (1). Expression (1) represents the relation between the thickness a of the radiation shielding members, i.e., the size along the direction of propagation of radiation, and the amount of radiation transmitting the radiation shielding members.
- where a is the thickness of the radiation shielding members along the direction of propagation of radiation, σa(E) is the absorption coefficient of the radiation shielding members with radiation having energy E, μ0 is the amount of radiation before transmitting the radiation shielding members and μ is the amount of radiation transmitting the radiation shielding members.
- It is known from Expression (1) that the greater radiation shielding members have higher radiation shielding ability. The thickness of the radiation shielding members necessary to secure the least necessary radiation shielding ability can be determined by using Expression (1).
- The upstream side surfaces of the
radiation shielding members radiation shielding members radiation shielding members - Referring to FIG. 3, a
radiation shielding member 6 in a modification has the shape of a round tube. The wall thickness a of theradiation shielding member 6 is a thickness necessary to secure necessary radiation shielding effect determined by using Expression (1). The radiation shielding ability of theradiation shielding member 6 having the shape of a round tube is equivalent to that of the radiation shielding members having the shape of a rod. - A radioactive substance storage facility1A in a second embodiment according to the present invention will be described with reference to FIG. 4. As shown in FIG. 4,
radiation shielding members 6 a are attached to the upstream side surfaces ofstorage tubes 2, andradiation shielding members 6 b are attached to the downstream side surfaces of thestorage tubes 2. Thestorage tubes 2 combined with theradiation shielding members 6 a are arranged in two rows adjacent to anopening 8A, and thestorage tubes 2 combined with theradiation shielding members 6 b are arranged in two rows adjacent to anopening 9A. The second embodiment, similarly to the first embodiment shown in FIG. 1, is capable of greatly reducing the amount of radiation that reaches theopenings 8A and 8B. -
- where Δθ is increase in temperature, δ is the thickness of the radiation shielding member and λ is the thermal conductivity of the radiation shielding member.
- The radiation shielding ability and the heat removing ability of the
storage tube 2 combined with the radiation shielding member were calculated by using Expressions (1) and (2), in which it was assumed that the energy of radiation is 1 MeV and the radiation shielding member is made of iron. Calculated values are shown in FIG. 5. It is known from FIG. 5 that the radiation attenuation ratio is about 1/100 when the thickness of the radiation shielding member is 10 cm and gamma rays of 1 MeV in energy is radiated. Heat generated by the spent fuel assemblies is transmitted through thestorage tube 2 to the radiation shielding member. Increase in temperature of the surface of thestorage tube 2 is about 0.1° when the heat flux across the radiation shielding member is 100 W/m, and is about 1° when 1 kW/m. Therefore, increase in temperature of thestorage tube 2 is small and the reduction of the heat removing ability of thestorage tube 2 is small when the energy of radiation or heat flux is on the level as mentioned above. - The second embodiment has the following effects. Since the radiation shielding members of the second row are joined to the storage tubes to eliminate spaces between them, the
storage room 3 can be formed in a short length, i.e., a size along the direction of flow of air. - A dry radioactive substance storage facility1B in a third embodiment according to the present invention will be described with reference to FIG. 6. In the radioactive substance storage facility 1B,
storage tubes 2 are arranged in lines and rows in astorage room 3.Radiation shielding members 6 a are arranged in a single row on the side of anopening 8A so as to correspond directly to theadjacent storage tubes 2, respectively.Radiation shielding members 6 b are arranged in a single row on the side of anopening 9A so as to correspond directly to theadjacent storage tubes 2, respectively. The radioactive substance storage facility 1B in the third embodiment differs from the radioactive substance storage facility 1 in the first embodiment in the arrangement of thestorage tubes 2. Although the dry radioactive substance storage facility in the third embodiment attenuates the amount of radiation reaching theopenings radiation shielding members openings - A dry radioactive substance storage facility1C in a fourth embodiment according to the present invention will be described with reference to FIG. 7. In a
storage room 3 of the radioactive substance storage facility 1C,storage tubes 2 are arranged, similarly to those of the dry radioactive substance storage facility 1B, in lines and rows.Radiation shielding members 6 a on the side of anopening 8A are arranged in two rows in a triangular array arrangement.Radiation shielding members 6 b on the side of anopening 9A are arranged in two rows in a triangular array arrangement. The dry radioactive substance storage facility 1C is the same in effect as the dry radioactive substance storage facility 1. - A dry radioactive substance storage facility1D in a fifth embodiment according to the present invention will be described with reference to FIG. 8.
Radiation shielding members storage room 3 of the dry radioactive substance storage facility 1D. Theradiation shielding members air flow 7. The dry radioactive substance storage facility 7D is the same in effect as the dry radioactive substance storage facility 1. Theradiation shielding members air flow 7 have increased radiation attenuating effect. Therefore, the amount of radiation reaching theopenings - A dry radioactive substance storage facility1E in a sixth embodiment according to the present invention will be described with reference to FIG. 9.
Storage tubes 2 are arranged in astorage room 3 of the dry radioactive substance storage facility 1E in an arrangement similar to that of thestorage tubes 2 of the dry radioactive substance storage facility 1A.Radiation shielding members 6 a, similarly to those of the dry radioactive substance storage facility 1A shown in FIG. 4, are attached to the upstream side surfaces of thestorage tubes 2 in two rows adjacent to anopening 8A.Radiation shielding members 6 b, similarly to those of the dry radioactive substance storage facility 1A, are attached to the downstream side surfaces of thestorage tubes 2 in two rows adjacent to anopening 9A. Theradiation shielding members radiation shielding members 6 a are disposed with their edges directed in a direction opposite the direction ofair flow 7 and theradiation shielding members 6 b are disposed with their edges direction in the direction ofair flow 7, theradiation shielding members air flow 7. - A dry radioactive substance storage facility1F in a seventh embodiment according to the present invention will be described with reference to FIG. 10. The dry radioactive substance storage facility 1F has a building of reinforced concrete institution having a
fuel storage room 3. Only matters relating to the dry radioactive substance storage facility 1F different from those of the dry radioactive substance storage facility 1 will be described. A plurality ofbaffling plates 6 d are arranged in thestorage room 3 near an air inlet duct. A plurality ofbaffling plates 6 d are arranged in thestorage room 3 near an stack.Radiation scattering member 21A is disposed on the side of the air inlet duct with respect to thebaffling plates 6 c and is attached to a side wall of thestorage room 3, facing thebaffling plates 6 c.Radiation scattering member 21B is disposed on the side of the stack with respect to thebaffling plates 6 d and is attached to a side wall of thestorage room 3, facing thebaffling plates 6 d. - As shown in FIG. 11, each of the
baffling plates neutron shielding member 12 with a gammaray shielding member 13. Theneutron shielding member 12 is made of a stainless steel containing a neutron absorbing substance, such as boron. The stainless steel containing boron is strong and is suitable for forming the structural member of the baffling plate. Theneutron shielding member 12 may be formed of a substance containing iron, such as a carbon steel. The gammaray shielding member 13 may be formed of a hydrogen compound, such as a hydrocarbon. - The
baffling plates ceiling slab 10 and the floor slab 11. Some of thebaffling plates 6 d are arranged so that upper ones are shifted toward the stack relative to the lower ones. Thebaffling plates 6 c are inclined upward toward thestorage tubes 2. - As shown in FIG. 12, the
radiation scattering member 21B, similarly to thebaffling plates neutron shielding member 12 with a gammaray shielding member 13. Theradiation scattering member 21A is the same in construction as theradiation scattering member 21B. Each of theradiation scattering members surfaces 14 facing obliquely downward andhorizontal surfaces 15 facing upward on its side facing the baffling plates. The inclined surfaces 14 and thehorizontal surfaces 15 form a sawtoothed side surface. - Air supplied through the
air inlet duct 8 flows through spaces between thebaffling plates 6 c into spaces between thestorage tubes 2 disposed in thestorage room 3. The air flowing through the spaces between thestorage tubes 2 cools thestorage tubes 2 and remove decay heat generated by the spent fuel assemblies contained in thestorage tubes 2 The air heated by decay heat flows through spaces between thebaffling plates 6 d and thestack 9 and is discharged outside. - The
baffling plates neutron shielding member 12 and the gammaray shielding member 13 are capable of shielding neutrons and gamma rays. Thus, thebaffling plates storage tubes 2 is not attenuate by thebaffling plates neutron shielding member 12 is covered with the gammaray shielding member 13, the gammaray shielding member 13 can be easily fixed to theneutron shielding member 12. For example, the gammaray shielding member 13 may be attached to the surface to theneutron shielding member 12 via an adhesive. Thebaffling plates radiation shielding members - Radioactive rays (neutrons and gamma rays) emitted by the spent fuel assemblies stored in the
storage room 3 are intercepted by concrete walls defining thestorage room 3 including theceiling slab 10 and the floor slab 11. Radiation that propagate toward thestack 9 is intercepted by thebaffling plates 6 d. Thebaffling plates 6 d formed by combining the neutron absorbing member and the gamma ray absorbing member are capable of efficiently shielding neutrons and gamma rays. The radiation shielding function of thebaffling plates 6 d will be described with reference to FIG. 11 typically showing thebaffling plates 6 d, and radiation 16 (including neutrons and gamma rays) propagating obliquely upward and falling on thebaffling plates 6 d. The radiation shielding ability of thebaffling plate 6 d is expressed by: - where b is the thickness of the
neutron shielding member 12 of the baffling plate 63 along the path of theradiation 16, a is the thickness of the gammaray shielding member 13 along the path of theradiation 16, μ0 is the amount of energy of theradiation 16 before transmitting thebaffling plate 6B, μ is the amount of energy of theradiation 16 transmitting throgh thebaffling plate 6B, σb is the absorption coefficient of theneutron shielding member 12 to theradiation 16 having energy E, and σa is the absorption coefficient of the gammaray shielding member 13 to theradiation 16. As obvious from Expression (3), the radiation shielding ability increases with the increase in the thicknesses of theneutron shielding member 12 and the gammaray shielding member 13. Since thebaffling plates 6 d are arranged vertically so as to overlap each other and some of thebaffling plates 6 d are arranged so that upper ones are shifted toward the stack relative to the lower ones, theradiation 16 propagating obliquely upward are intercepted by the plurality ofbaffling plates 6 d. Accordingly, the radiation (neutrons and gamma rays) propagating toward thestack 9 can efficiently be intercepted. - Since the
baffling plates 6 c are inclined upward toward thestorage tubes 2, air is supplied into an upper region of thestorage room 3 in which the temperature is high, the temperature of thestorage room 3 can be lowered. The shielding ability of thebaffling plates 6 c will be described. Part ofradiation 17 propagating toward thebaffling plates 6 c and trying to penetrate thebaffling plates 6 c is attenuated by thebaffling plates 6 c, and part of theradiation 17 is reflected downward by the inclined surfaces of thebaffling plates 6 c, theradiation 18 reflected downward is attenuated by thelower baffling plates 6 c. The radiation reflected by theinclined baffling plates 6 c does not propagate toward theair inlet duct 8 and propagate downward necessarily. Thebaffling plates 6 c exercise both a radiation attenuating function and a radiation reflecting function, whereby the radiation propagating toward theair inlet duct 8 is attenuate significantly. - The function of the
radiation scattering member 21B will be explained. Theradiation 17 propagated through spaces between thebaffling plates 6 d is attenuated by theneutron shielding member 12 and the gammaray shielding member 13 of theradiation scattering member 21B. Part ofradiation 19 falling on theinclined surfaces 14 are reflected downward and is attenuated by lower portions of theradiation scattering member 21B below theinclined surfaces 14 reflecting theradiation 19 or by the floor slab 11. Theradiation scattering member 21B does not reflect the radiation upward, the amount of the radiation propagating toward thestack 9 is further attenuate. Since theradiation scattering member 21B is disposed in an inherently dead space through which air flows scarcely, theradiation scattering member 21B does not increase pressure loss in the air passage and does not attenuate the ability to cool the spent fuel assemblies. Since theradiation scattering member 21B is formed by covering theneutron shielding member 12 with the gammaray shielding member 13, similarly to the baffling plates, the gammaray shielding member 13 can simply be attached to theneutron shielding member 12. Theradiation scattering member 21A is the same in function as theradiation scattering member 21B and attenuates the amount of radiation that propagates toward theair inlet duct 8. - Referring to FIG. 14, a radiation scattering member21C in a modification has a surface facing the baffling plates and having the shape of comb teeth. The radiation scattering member 21C is formed, similarly to the
radiation scattering members neutron shielding member 12 with a gammaray shielding member 13. - Although the present invention has been described in its preferred embodiments as applied to cooling the
storage tubes 2 containing the spent fuel assemblies, the present invention is effectively applicable also to storing vitrified radioactive wastes instead of the spent fuel assemblies.
Claims (17)
Priority Applications (1)
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US09/961,299 US6501814B1 (en) | 1998-12-24 | 2001-09-25 | Dry radioactive substance storage facility |
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JP36631798A JP2000187100A (en) | 1998-12-24 | 1998-12-24 | Facility for dry storage of radioactive substance |
JP10-366317 | 1998-12-24 | ||
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JP36895198A JP3921856B2 (en) | 1998-12-25 | 1998-12-25 | Radioactive material dry storage facility |
US09/468,317 US6430248B1 (en) | 1998-12-24 | 1999-12-21 | Dry radioactive substance storage facility |
US09/961,299 US6501814B1 (en) | 1998-12-24 | 2001-09-25 | Dry radioactive substance storage facility |
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US20100163734A1 (en) * | 2006-08-11 | 2010-07-01 | Raymond John Proctor | Bulk material analyzer assembly including structural beams containing radiation shielding material |
US20160163406A1 (en) * | 2013-07-31 | 2016-06-09 | Joint Stock Company "Akme-Engineering" | Method for long-term storage of waste nuclear fuel |
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TW444209B (en) * | 1998-12-24 | 2001-07-01 | Hitachi Ltd | Radioactive material dry storage facility |
FR2814274B1 (en) * | 2000-09-15 | 2002-11-29 | Commissariat Energie Atomique | INSTALLATION FOR STORING IRRADIATED FUEL OR RADIOACTIVE MATERIAL |
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US20100163734A1 (en) * | 2006-08-11 | 2010-07-01 | Raymond John Proctor | Bulk material analyzer assembly including structural beams containing radiation shielding material |
US8138480B2 (en) * | 2006-08-11 | 2012-03-20 | Thermo Fisher Scientific Inc. | Bulk material analyzer assembly including structural beams containing radiation shielding material |
US20160163406A1 (en) * | 2013-07-31 | 2016-06-09 | Joint Stock Company "Akme-Engineering" | Method for long-term storage of waste nuclear fuel |
US9899111B2 (en) * | 2013-07-31 | 2018-02-20 | Joint Stock Company “Akme-Engineering” | Method for long-term storage of waste nuclear fuel |
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