CA2246064A1 - Fuel assembly for heavy-water moderated nuclear reactor - Google Patents
Fuel assembly for heavy-water moderated nuclear reactor Download PDFInfo
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- CA2246064A1 CA2246064A1 CA002246064A CA2246064A CA2246064A1 CA 2246064 A1 CA2246064 A1 CA 2246064A1 CA 002246064 A CA002246064 A CA 002246064A CA 2246064 A CA2246064 A CA 2246064A CA 2246064 A1 CA2246064 A1 CA 2246064A1
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- Prior art keywords
- fuel
- heavy
- rods
- water
- fuel rods
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- 239000000446 fuel Substances 0.000 title claims abstract description 243
- XLYOFNOQVPJJNP-ZSJDYOACSA-N Heavy water Chemical compound [2H]O[2H] XLYOFNOQVPJJNP-ZSJDYOACSA-N 0.000 title claims abstract description 100
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 29
- 238000000034 method Methods 0.000 claims description 11
- 125000006850 spacer group Chemical group 0.000 claims description 5
- 230000002093 peripheral effect Effects 0.000 claims description 2
- 239000002915 spent fuel radioactive waste Substances 0.000 abstract description 12
- 230000000712 assembly Effects 0.000 abstract description 10
- 238000000429 assembly Methods 0.000 abstract description 10
- 238000005253 cladding Methods 0.000 description 8
- 239000008188 pellet Substances 0.000 description 7
- 238000009835 boiling Methods 0.000 description 5
- 230000002285 radioactive effect Effects 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 230000005855 radiation Effects 0.000 description 2
- 238000003466 welding Methods 0.000 description 2
- 229910052770 Uranium Inorganic materials 0.000 description 1
- 239000002826 coolant Substances 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000005304 joining Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000003758 nuclear fuel Substances 0.000 description 1
- 239000002901 radioactive waste Substances 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- JFALSRSLKYAFGM-UHFFFAOYSA-N uranium(0) Chemical compound [U] JFALSRSLKYAFGM-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
- G21C3/30—Assemblies of a number of fuel elements in the form of a rigid unit
- G21C3/32—Bundles of parallel pin-, rod-, or tube-shaped fuel elements
- G21C3/34—Spacer grids
- G21C3/344—Spacer grids formed of assembled tubular elements
-
- 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
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- General Engineering & Computer Science (AREA)
- High Energy & Nuclear Physics (AREA)
- Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
- Monitoring And Testing Of Nuclear Reactors (AREA)
Abstract
A fuel assembly for a heavy-water reactor which is composed while using at least partially spent fuel rods (4) from a light-water reactor. The spent fuel rods are obtained from fuel assemblies which comprise a plurality of short fuel units stacked on top of each other. The fuel units comprise fuel rods arranged between two end plates.
Description
.
FUEL ASSEMBLY FOR HEAVY-WATER MODERATED NUCLEAR REACTOR
TECHNICAL FIELD
The present invention relates to a fuel assembly for insertion into a pressure tube in a heavy-water moderated reactor, wherein the fuel assembly is composed while using spent fuel rods from a light-water reactor.
BACKGROUND ART
Since heavy water is a moderator with less neutron absorption than light water, a heavy-water moderated reactor may be operated with a lower content of fissile material than a light-water moderated reactor. A light-water reactor requires fuel which is enriched to a certain level. Therefore, the possibility of using spent fuel from light-water reactors as fuel in heavy-water moderated nuclear reactors has been discussed. Since the reactors are composed in completely different ways, also the fuel looks different. To be able to use fuel from a light-water reactor in a heavy-water reactor, the fuel must be reconstituted and adapted to the new reactor. This is a great problem since the fuel emits high amounts of radioactive radiation. It is preferable to handle the spent fuel as little as possible.
A large number of different solutions have been proposed as regards how to reconstitute the spent fuel, but these different methods all have the above-mentioned disadvantage of requiring a great deal of handling of the radioactive fuel.
A heavy-water moderated reactor of a so-called CANDU type comprises a plurality of horizontal cylindrical pressure tubes. Each one of the pressure tubes have an inlet end into which fresh fuel assemblies are inserted with the aid of a special fuel charging/discharging machine, and an outlet end from which burnt-out fuel assembiies emerge. A fuel assembly has a length of about half a metre. A pressure tube at the same time contains a plurality of fuel assemblies with different degrees of burnup. The fuel assemblies have a circular cross section and the fuel rods are arranged in a polar lattice.
In a light-water reactor, the core comprises a plurality of fuel assemblies arranged vertically in the core in a certain spaced relationship to each other. A fuel assembly comprises a plurality of fuel rods, each of which contains a stack of pellets of a nuclear fuel arranged in a cladding tube. The length of the fuel assembly corresponds to the height of the core and is about 4 m. When the fuel is spent, the whole fuel assembly is replaced by a fresh assembly. The fuel assembly has a square cross section and the fuel rods are arranged in an orthogonal lattice.
The fuel assemblies for a light-water moderated reactor and a heavy-water moderated reactor differ from each other primarily in that the latter is much shorter and in that they have different lattices and different external shape.
The journal "Nuclear Europe Worldscan", No. 3-4 March-April 1997, contains on page 58 an article entitled "Progress report on Canada/Korea/US study of PWR spent fuel in Candu".
It describes a method in which spent nuclear fuel from a pressurized-water reactor (PWR) is reconstituted into fuel for a heavy-water reactor. The method comprises the following steps:
- removing the cladding on the old pellets, - converting the old pellets by a special process into a powder capable of being sintered, - manufacturing new pellets by means of sintering of this powder, - inserting the pellets into new cladding tubes, - assembling the fuel assembly, and - taking care of old cladding and other radioactive waste for deposition.
One of the disadvantages of this method is that it takes about ten years before the radioactivity in the fuel has decayed to a sufficient extent for a reconstitution of the fuel to be carried out.
In article entitled "CANDU Fuel Cycle Flexibility" by D.F.
Torgerson, P.G. Boczar, A.R. Dastur, presented at the ninth Pacific Basin Nuclear Conference in Sydney, Australia, 1994 May 1-6, the possibility is mentioned of reconstituting fuel rods from PWR reactors by first shortening them and then assembling a fuel assembly adapted for a heavy-water reactor with the shortened fuel rods. In this way, it is not necessary to manufacture new pellets from the used fuel. A
problem in this connection is how to achieve a tight cladding around the shortened fuel rod in a simple manner. A solution which is mentioned comprises inserting the shortened rod into a new cladding tube which is then sealed at the ends with new end plugs. This results in the fuel rod having double cladding tubes, which leads to a deteriorated heat transfer between the fuel and the coolant, and increased neutron absorption.
Common to these solutions is that they are based on PWR fuel assemblies which have fuel rods, the length of which corresponds to the length of the fuel assemblies. One of the problems which arises is that the fuel rods are too long to fit in a heavy-water reactor.
Patent document PCT/SE95/01478 shows a fuel assembly for a boiling water reactor (BWR) which comprises a plurality of fuel units, stacked on top of each other, each of which comprising a plurality of fuel rods extending between a top 5 tie plate and a bottom tie plate. The fuel units are surrounded by a common fuel channel with a substantially square cross section.
PCT/SE97/01082 (WO 97/49098) shows a fuel assembly for a PWR, 10 which also comprises a plurality of fuel units stacked on top of each other, each one comprising a plurality of fuel rods extending between a top nozzle and a bottom nozzle.
SU~ARY OF THE INVENTION
The invention aims to provide a method for rapidly and simply reconstituting spent nuclear fuel from a light-water reactor to a fuel assembly for a heavy-water reactor.
20 The invention also aims to provide a fuel assembly intended for use in a heavy-water reactor which comprises a plurality of spent fuel rods from a light-water reactor.
What characterizes a method and a fuel assembly according to 25 the invention will become clear from the appended claims.
According to the invention, the starting-point are fuel rods which have been included in a fuel assembly which is composed of a plurality of short fuel units. In this way, the problem 30 of having to shorten fuel rods is avoided.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows a known fuel assembly for a boiling water 35 reactor moderated by light water.
Flgure 2 shows a section A-A through the fuel assembly in Figure 1.
Figure 3 shows a fuel assembly for a heavy-water moderated nuclear reactor according to a first embodiment of the invention.
Figure 4 shows a fuel assembly for a heavy-water moderated nuclear reactor according to a second embodiment of the invention.
Figures 5 and 6 show in a section B-B through the fuel assembly in Figure 3 two different lattice configurations for the fuel rods.
Figure 7 shows a fuel assembly for a heavy-water moderated nuclear reactor according to a third embodiment of the invention.
Figure 8 shows a fuel assembly for a heavy-water moderated nuclear reactor according to a fourth embodiment of the invention.
Figure 9 shows a section C-C through the fuel assembly in Figure 7.
Figure 10 shows a section D-D through the fuel assembly in Figure 8.
Figures 11-13 show additional lattice configurations for the fuel rods.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 shows a known fuel assembly for a boiling water reactor moderated by light water (BWR). The fuel assembly comprises an upper handle 1, a lower end portion 2 and a plurality of fuel units 3 stacked on top of each other. Each fuel unit comprises a plurality of fuel rods 4 arranged in parallel and in a definite space relationship to each other in a given lattice, and a top tie plate 5 and a bottom tie plate 6 for attachment of the fuel rods in their respective positions in the lattice. The fuel units 3 are stacked on top of each other in the longitudinal direction of the fuel assembly and they are stacked in such a way that the top tie plate 5 in one fuel unit is facing the bottom tie plate 6 in the next fuel unit in the stack, and such that the fuel rods in all the fuel elements are parallel to each other. A fuel rod 4 comprises fuel in the form of a stack of pellets 7 of uranium arranged in a cladding tube 10.
Figure 2 shows a section A-A through the fuel assembly in Figure 1. The fuel units are enclosed in a fuel channel 8 with a substantially s~uare cross section. The fuel channel is provided with a support member 9 of cruciform cross section which is secured to the four walls of the fuel channel. The fuel channel with the support member surrounds four vertical channel-formed parts 11, so-called sub-channels, with an at least substantially square cross section. The four sub-channels each contain a stack of fuel units. Each fuel unit comprises 24 fuel rods 4 arranged in a symmetrical 5x5 lattice.
According to the invention, a heavy-water moderated fuel assembly is composed of fuel rods from burnt-out fuel units, for example those shown in Figures 1 and 2. One of the problems which have to be solved when using fuel rods from light-water reactors in a fuel assembly for a heavy-water reactor is how to design the fuel assembly for guiding towards the pressure tube and for support between the rods.
In a fuel assembly for a heavy-water reactor, each fuel rod is provided with a number of support pads for these purposes.
No such pads are provided on light-water fuel rods.
Admittedly, it is possible to add pads to the spent light-water fuel, but because of the radioactive radiation, it is preferable to avoid this.
In one embodiment of the invention, the fuel unit is dismantled by removing the bottom tie plate and the top tie plate from the fuel rods. The end surfaces of the fuel rods are prepared for new welding. Thereafter, the fuel rods are arranged in a new lattice configuration and new end plates, intended for the heavy-water reactor, are welded on.
Figure 3 shows a fuel assembly for a heavy-water moderated reactor in which all the fuel rods 4 originate from the BWR
units 3 in Figure 1. In this embodiment, the fuel rods in the fuel units have a length corresponding to the length of a heavy-water fuel assembly, that is, about 0.5 m. The fuel assembly comprises a fuel unit 16c which comprises a plurality of BWR fuel rods 4 arranged in parallel with each other between two end plates 13a and 13b. The end plates are provided with support surfaces 15 for guiding towards the pressure tube. To keep the fuel rods spaced apart from each other and provide support for the fuel rods, a spacer 12 is arranged between the end plates. The spacer is designed so as also to function as support against the pressure tube. Thus, such a fuel assembly have three support surfaces against the pressure tube, two on the end plates and one on the spacer.
This is sufficient to guide the assembly towards the pressure tube.
Figure 4 also shows a fuel assembly for a heavy-water moderated reactor in which all the fuel rods 4 ori~inate from the fuel units 3 in Figure 1. In this embodiment, the fuel rods in the fuel units have a length corresponding to half the length of a heavy-water fuel assembly, that is, about 0.25 m. The fuel assembly comprises two fuel units 16a and 16b, each of which comprises a plurality of spent BWR fuel rods 4 arranged between two end plates 14a, 14b, 14c and 14d.
The two fuel units 16a, 16b are joined into a fuel assembly.
The joining of the fuel units takes place by welding together two end plates. All the end plates are provided with support surfaces 15 for guiding towards the pressure tube.
It is also possible to start from a BWR fuel with a rod length different from that of the above example, if only these together result in the same core length and the fuel discharging machine may be adapted thereto.
Figures 5 and 6 show two feasible lattice configurations for the fuel assemblies shown in Figures 3 and 4. Since BWR fuel rods are normally thinner than fuel rods intended for heavy-water reactors, a larger number of fuel rods are required in a fuel assembly with recycled BWR fuel than in a fuel assembly with fresh fuel. Figure 5 shows a fuel assembly with 52 fuel rods arranged in an orthogonal lattice. An advantage of such a lattice is that a spacer for intermediate support may be designed in accordance with well-known BWR technology.
Figure 6 shows a fuel assembly with 55 fuel rods arranged in a polar lattice.
Figures 7 and 8 show two embodiments of a fuel assembly according to the invention which comprises both spent BWR
fuel rods 4 and fresh fuel rods 23, 24 intended for a heavy-water reactor. The spent fuel rods are arranged in the central part of the fuel assembly and the fresh ones are arranged in the peripheral part of the fuel assembly. The fresh fuel rods are provided with support pads 17 for supporting against the pressure tube and adjacent fuel rods.
Figure 7 shows a fuel assembly in which the spent fuel rods 4 have a length which is equal to the length of the fuel assembly. The fuel assembly has two end plates 18. These need not be provided with support surfaces as in the preceding example since the outer fuel rods are provided with support pads. Figure 9 shows a section through the fuel assembly in Figure 7. The fuel assembly contains 28 BWR fuel rods 4, the diameter of which is 9 mm and 32 fresh heavy-water fuel rods 23, the diameter of which is 10 mm. The fuel assembly has a diameter which is 102 mm.
In another embodiment of the invention, the fuel unit is not dismantled, but instead the whole fuel unit is used as it is.
The fuel unit is thus allowed to retain its original lattice configuration and its BWR end plates. A fuel assembly for a heavy-water reactor is composed by mounting fresh heavy-water fuel 24 around the BWR fuel unit.
PCT/SE97/02020 (WO 98/28753) shows a fuel assembly for a boiling water reactor which comprises a plurality of short fuel units stacked on top of each other. The fuel units have fuel rods arranged in a polar lattice between two end plates.
Such a fuel unit already has a lattice which is suitable for a heavy-water reactor and according to one embodiment of the invention, it is reconstructed into a fuel assembly for a heavy-water reactor without being dismantled. Fresh fuel rods are mounted around the fuel unit and new end plates are welded together with the old BWR end plates to keep the fresh fuel in position.
Figure 8 shows two such BWR fuel units 21 and 22 which are joined to each other. The fuel units together have a length which corresponds to the length of a heavy-water fuel rod 23.
The BWR end plates 19 are joined to new annular end plates 20. Before the end plates are welded together, an adjustment of the outer contours of the BWR end plates takes place.
- 35 Figure 10 shows a section through the fuel assembly which is shown in Figure 8. The BWR fuel units contain 28 fuel rods 4, the diameter of which is 9 mm and they are surrounded by 16 fresh heavy-water rods 24 with a diameter which is 14 mm. The diameter of the fuel assembly is 102 mm.
Figures 11, 12 och 13 show three different embodiments wherein a BWR fuel unit 30 with an orthogonal lattice has been rebuilt into a fuel assembly for a heavy-water reactor.
The fuel unit 30 is not dismantled but the whole unit is used as it is. The BWR fuel unit contains 24 fuel rods 26, the diameter of which is 10 mm.
In Figure 11 the fuel unit is surrounded by 12 fresh heavy-water rods 27, the diameter of which is 13 mm and 9 heavy-water rods 28, the diameter of which is 10 mm. In Figure 12 the fuel unit is surrounded by 16 fresh heavy-water rods, the diameter of which is 13 mm. In Figure 13 the fuel unit is surrounded by 12 fresh heavy-water rods 29, the diameter of which is 14 mm, plus any completion of fuel rod in the oblique corner.
The embodiments shown above are based on fuel assemblies for boiling water reactors. PCT/SE97/01082 (WO 97/49098) shows a fuel assembly for a PWR which also comprises a plurality of short fuel units stacked on top of each other, each fuel unit comprising a plurality of fuel rods extending between a top tie plate and a bottom tie plate. The invention is, of course, also applicable to short fuel units intended for a pressurized-water reactor.
One condition for the invention is that the length of the fuel rods in the light-water fuel assembly has been chosen such that they may be used in a heavy-water reactor without having to open and modify the fuel rods.
FUEL ASSEMBLY FOR HEAVY-WATER MODERATED NUCLEAR REACTOR
TECHNICAL FIELD
The present invention relates to a fuel assembly for insertion into a pressure tube in a heavy-water moderated reactor, wherein the fuel assembly is composed while using spent fuel rods from a light-water reactor.
BACKGROUND ART
Since heavy water is a moderator with less neutron absorption than light water, a heavy-water moderated reactor may be operated with a lower content of fissile material than a light-water moderated reactor. A light-water reactor requires fuel which is enriched to a certain level. Therefore, the possibility of using spent fuel from light-water reactors as fuel in heavy-water moderated nuclear reactors has been discussed. Since the reactors are composed in completely different ways, also the fuel looks different. To be able to use fuel from a light-water reactor in a heavy-water reactor, the fuel must be reconstituted and adapted to the new reactor. This is a great problem since the fuel emits high amounts of radioactive radiation. It is preferable to handle the spent fuel as little as possible.
A large number of different solutions have been proposed as regards how to reconstitute the spent fuel, but these different methods all have the above-mentioned disadvantage of requiring a great deal of handling of the radioactive fuel.
A heavy-water moderated reactor of a so-called CANDU type comprises a plurality of horizontal cylindrical pressure tubes. Each one of the pressure tubes have an inlet end into which fresh fuel assemblies are inserted with the aid of a special fuel charging/discharging machine, and an outlet end from which burnt-out fuel assembiies emerge. A fuel assembly has a length of about half a metre. A pressure tube at the same time contains a plurality of fuel assemblies with different degrees of burnup. The fuel assemblies have a circular cross section and the fuel rods are arranged in a polar lattice.
In a light-water reactor, the core comprises a plurality of fuel assemblies arranged vertically in the core in a certain spaced relationship to each other. A fuel assembly comprises a plurality of fuel rods, each of which contains a stack of pellets of a nuclear fuel arranged in a cladding tube. The length of the fuel assembly corresponds to the height of the core and is about 4 m. When the fuel is spent, the whole fuel assembly is replaced by a fresh assembly. The fuel assembly has a square cross section and the fuel rods are arranged in an orthogonal lattice.
The fuel assemblies for a light-water moderated reactor and a heavy-water moderated reactor differ from each other primarily in that the latter is much shorter and in that they have different lattices and different external shape.
The journal "Nuclear Europe Worldscan", No. 3-4 March-April 1997, contains on page 58 an article entitled "Progress report on Canada/Korea/US study of PWR spent fuel in Candu".
It describes a method in which spent nuclear fuel from a pressurized-water reactor (PWR) is reconstituted into fuel for a heavy-water reactor. The method comprises the following steps:
- removing the cladding on the old pellets, - converting the old pellets by a special process into a powder capable of being sintered, - manufacturing new pellets by means of sintering of this powder, - inserting the pellets into new cladding tubes, - assembling the fuel assembly, and - taking care of old cladding and other radioactive waste for deposition.
One of the disadvantages of this method is that it takes about ten years before the radioactivity in the fuel has decayed to a sufficient extent for a reconstitution of the fuel to be carried out.
In article entitled "CANDU Fuel Cycle Flexibility" by D.F.
Torgerson, P.G. Boczar, A.R. Dastur, presented at the ninth Pacific Basin Nuclear Conference in Sydney, Australia, 1994 May 1-6, the possibility is mentioned of reconstituting fuel rods from PWR reactors by first shortening them and then assembling a fuel assembly adapted for a heavy-water reactor with the shortened fuel rods. In this way, it is not necessary to manufacture new pellets from the used fuel. A
problem in this connection is how to achieve a tight cladding around the shortened fuel rod in a simple manner. A solution which is mentioned comprises inserting the shortened rod into a new cladding tube which is then sealed at the ends with new end plugs. This results in the fuel rod having double cladding tubes, which leads to a deteriorated heat transfer between the fuel and the coolant, and increased neutron absorption.
Common to these solutions is that they are based on PWR fuel assemblies which have fuel rods, the length of which corresponds to the length of the fuel assemblies. One of the problems which arises is that the fuel rods are too long to fit in a heavy-water reactor.
Patent document PCT/SE95/01478 shows a fuel assembly for a boiling water reactor (BWR) which comprises a plurality of fuel units, stacked on top of each other, each of which comprising a plurality of fuel rods extending between a top 5 tie plate and a bottom tie plate. The fuel units are surrounded by a common fuel channel with a substantially square cross section.
PCT/SE97/01082 (WO 97/49098) shows a fuel assembly for a PWR, 10 which also comprises a plurality of fuel units stacked on top of each other, each one comprising a plurality of fuel rods extending between a top nozzle and a bottom nozzle.
SU~ARY OF THE INVENTION
The invention aims to provide a method for rapidly and simply reconstituting spent nuclear fuel from a light-water reactor to a fuel assembly for a heavy-water reactor.
20 The invention also aims to provide a fuel assembly intended for use in a heavy-water reactor which comprises a plurality of spent fuel rods from a light-water reactor.
What characterizes a method and a fuel assembly according to 25 the invention will become clear from the appended claims.
According to the invention, the starting-point are fuel rods which have been included in a fuel assembly which is composed of a plurality of short fuel units. In this way, the problem 30 of having to shorten fuel rods is avoided.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows a known fuel assembly for a boiling water 35 reactor moderated by light water.
Flgure 2 shows a section A-A through the fuel assembly in Figure 1.
Figure 3 shows a fuel assembly for a heavy-water moderated nuclear reactor according to a first embodiment of the invention.
Figure 4 shows a fuel assembly for a heavy-water moderated nuclear reactor according to a second embodiment of the invention.
Figures 5 and 6 show in a section B-B through the fuel assembly in Figure 3 two different lattice configurations for the fuel rods.
Figure 7 shows a fuel assembly for a heavy-water moderated nuclear reactor according to a third embodiment of the invention.
Figure 8 shows a fuel assembly for a heavy-water moderated nuclear reactor according to a fourth embodiment of the invention.
Figure 9 shows a section C-C through the fuel assembly in Figure 7.
Figure 10 shows a section D-D through the fuel assembly in Figure 8.
Figures 11-13 show additional lattice configurations for the fuel rods.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 shows a known fuel assembly for a boiling water reactor moderated by light water (BWR). The fuel assembly comprises an upper handle 1, a lower end portion 2 and a plurality of fuel units 3 stacked on top of each other. Each fuel unit comprises a plurality of fuel rods 4 arranged in parallel and in a definite space relationship to each other in a given lattice, and a top tie plate 5 and a bottom tie plate 6 for attachment of the fuel rods in their respective positions in the lattice. The fuel units 3 are stacked on top of each other in the longitudinal direction of the fuel assembly and they are stacked in such a way that the top tie plate 5 in one fuel unit is facing the bottom tie plate 6 in the next fuel unit in the stack, and such that the fuel rods in all the fuel elements are parallel to each other. A fuel rod 4 comprises fuel in the form of a stack of pellets 7 of uranium arranged in a cladding tube 10.
Figure 2 shows a section A-A through the fuel assembly in Figure 1. The fuel units are enclosed in a fuel channel 8 with a substantially s~uare cross section. The fuel channel is provided with a support member 9 of cruciform cross section which is secured to the four walls of the fuel channel. The fuel channel with the support member surrounds four vertical channel-formed parts 11, so-called sub-channels, with an at least substantially square cross section. The four sub-channels each contain a stack of fuel units. Each fuel unit comprises 24 fuel rods 4 arranged in a symmetrical 5x5 lattice.
According to the invention, a heavy-water moderated fuel assembly is composed of fuel rods from burnt-out fuel units, for example those shown in Figures 1 and 2. One of the problems which have to be solved when using fuel rods from light-water reactors in a fuel assembly for a heavy-water reactor is how to design the fuel assembly for guiding towards the pressure tube and for support between the rods.
In a fuel assembly for a heavy-water reactor, each fuel rod is provided with a number of support pads for these purposes.
No such pads are provided on light-water fuel rods.
Admittedly, it is possible to add pads to the spent light-water fuel, but because of the radioactive radiation, it is preferable to avoid this.
In one embodiment of the invention, the fuel unit is dismantled by removing the bottom tie plate and the top tie plate from the fuel rods. The end surfaces of the fuel rods are prepared for new welding. Thereafter, the fuel rods are arranged in a new lattice configuration and new end plates, intended for the heavy-water reactor, are welded on.
Figure 3 shows a fuel assembly for a heavy-water moderated reactor in which all the fuel rods 4 originate from the BWR
units 3 in Figure 1. In this embodiment, the fuel rods in the fuel units have a length corresponding to the length of a heavy-water fuel assembly, that is, about 0.5 m. The fuel assembly comprises a fuel unit 16c which comprises a plurality of BWR fuel rods 4 arranged in parallel with each other between two end plates 13a and 13b. The end plates are provided with support surfaces 15 for guiding towards the pressure tube. To keep the fuel rods spaced apart from each other and provide support for the fuel rods, a spacer 12 is arranged between the end plates. The spacer is designed so as also to function as support against the pressure tube. Thus, such a fuel assembly have three support surfaces against the pressure tube, two on the end plates and one on the spacer.
This is sufficient to guide the assembly towards the pressure tube.
Figure 4 also shows a fuel assembly for a heavy-water moderated reactor in which all the fuel rods 4 ori~inate from the fuel units 3 in Figure 1. In this embodiment, the fuel rods in the fuel units have a length corresponding to half the length of a heavy-water fuel assembly, that is, about 0.25 m. The fuel assembly comprises two fuel units 16a and 16b, each of which comprises a plurality of spent BWR fuel rods 4 arranged between two end plates 14a, 14b, 14c and 14d.
The two fuel units 16a, 16b are joined into a fuel assembly.
The joining of the fuel units takes place by welding together two end plates. All the end plates are provided with support surfaces 15 for guiding towards the pressure tube.
It is also possible to start from a BWR fuel with a rod length different from that of the above example, if only these together result in the same core length and the fuel discharging machine may be adapted thereto.
Figures 5 and 6 show two feasible lattice configurations for the fuel assemblies shown in Figures 3 and 4. Since BWR fuel rods are normally thinner than fuel rods intended for heavy-water reactors, a larger number of fuel rods are required in a fuel assembly with recycled BWR fuel than in a fuel assembly with fresh fuel. Figure 5 shows a fuel assembly with 52 fuel rods arranged in an orthogonal lattice. An advantage of such a lattice is that a spacer for intermediate support may be designed in accordance with well-known BWR technology.
Figure 6 shows a fuel assembly with 55 fuel rods arranged in a polar lattice.
Figures 7 and 8 show two embodiments of a fuel assembly according to the invention which comprises both spent BWR
fuel rods 4 and fresh fuel rods 23, 24 intended for a heavy-water reactor. The spent fuel rods are arranged in the central part of the fuel assembly and the fresh ones are arranged in the peripheral part of the fuel assembly. The fresh fuel rods are provided with support pads 17 for supporting against the pressure tube and adjacent fuel rods.
Figure 7 shows a fuel assembly in which the spent fuel rods 4 have a length which is equal to the length of the fuel assembly. The fuel assembly has two end plates 18. These need not be provided with support surfaces as in the preceding example since the outer fuel rods are provided with support pads. Figure 9 shows a section through the fuel assembly in Figure 7. The fuel assembly contains 28 BWR fuel rods 4, the diameter of which is 9 mm and 32 fresh heavy-water fuel rods 23, the diameter of which is 10 mm. The fuel assembly has a diameter which is 102 mm.
In another embodiment of the invention, the fuel unit is not dismantled, but instead the whole fuel unit is used as it is.
The fuel unit is thus allowed to retain its original lattice configuration and its BWR end plates. A fuel assembly for a heavy-water reactor is composed by mounting fresh heavy-water fuel 24 around the BWR fuel unit.
PCT/SE97/02020 (WO 98/28753) shows a fuel assembly for a boiling water reactor which comprises a plurality of short fuel units stacked on top of each other. The fuel units have fuel rods arranged in a polar lattice between two end plates.
Such a fuel unit already has a lattice which is suitable for a heavy-water reactor and according to one embodiment of the invention, it is reconstructed into a fuel assembly for a heavy-water reactor without being dismantled. Fresh fuel rods are mounted around the fuel unit and new end plates are welded together with the old BWR end plates to keep the fresh fuel in position.
Figure 8 shows two such BWR fuel units 21 and 22 which are joined to each other. The fuel units together have a length which corresponds to the length of a heavy-water fuel rod 23.
The BWR end plates 19 are joined to new annular end plates 20. Before the end plates are welded together, an adjustment of the outer contours of the BWR end plates takes place.
- 35 Figure 10 shows a section through the fuel assembly which is shown in Figure 8. The BWR fuel units contain 28 fuel rods 4, the diameter of which is 9 mm and they are surrounded by 16 fresh heavy-water rods 24 with a diameter which is 14 mm. The diameter of the fuel assembly is 102 mm.
Figures 11, 12 och 13 show three different embodiments wherein a BWR fuel unit 30 with an orthogonal lattice has been rebuilt into a fuel assembly for a heavy-water reactor.
The fuel unit 30 is not dismantled but the whole unit is used as it is. The BWR fuel unit contains 24 fuel rods 26, the diameter of which is 10 mm.
In Figure 11 the fuel unit is surrounded by 12 fresh heavy-water rods 27, the diameter of which is 13 mm and 9 heavy-water rods 28, the diameter of which is 10 mm. In Figure 12 the fuel unit is surrounded by 16 fresh heavy-water rods, the diameter of which is 13 mm. In Figure 13 the fuel unit is surrounded by 12 fresh heavy-water rods 29, the diameter of which is 14 mm, plus any completion of fuel rod in the oblique corner.
The embodiments shown above are based on fuel assemblies for boiling water reactors. PCT/SE97/01082 (WO 97/49098) shows a fuel assembly for a PWR which also comprises a plurality of short fuel units stacked on top of each other, each fuel unit comprising a plurality of fuel rods extending between a top tie plate and a bottom tie plate. The invention is, of course, also applicable to short fuel units intended for a pressurized-water reactor.
One condition for the invention is that the length of the fuel rods in the light-water fuel assembly has been chosen such that they may be used in a heavy-water reactor without having to open and modify the fuel rods.
Claims (10)
1. A method in a nuclear heavy-water reactor, characterized in that it comprises the following steps:
- fuel rods (4, 26) in a light-water reactor, in which light-water reactor the fuel rods are arranged extending between two end plates (5, 6) forming a short fuel unit (3), and in which several short fuel units are arranged stacked on top of each other forming a fuel assembly, whereby the fuel rods are at least partially burnt out, are withdrawn from the light-water reactor as separate fuel rods or as a group of fuel rods arranged in the fuel unit (3) and are moved into a pressure tube in the heavy-water reactor, - the fuel rods are additionally burnt out in the heavy-water reactor.
- fuel rods (4, 26) in a light-water reactor, in which light-water reactor the fuel rods are arranged extending between two end plates (5, 6) forming a short fuel unit (3), and in which several short fuel units are arranged stacked on top of each other forming a fuel assembly, whereby the fuel rods are at least partially burnt out, are withdrawn from the light-water reactor as separate fuel rods or as a group of fuel rods arranged in the fuel unit (3) and are moved into a pressure tube in the heavy-water reactor, - the fuel rods are additionally burnt out in the heavy-water reactor.
2. A method according to claim 1, characterized in that the end plates (5, 6) of the short fuel unit (3) are dismantled, whereupon the fuel rods are arranged in a new lattice and new end plates (13a, 13b, 14a, 14b, 14c, 14d) intended for the heavy-water reactor are mounted to the fuel rods.
3. A method according to claim 2, characterized in that the fuel rods are arranged centrally in the lattice and in that at least some fuel rod with fresh heavy-water fuel (23, 24, 27, 28, 29) is arranged in the peripheral part of the lattice.
4. A method according to claim 1, characterized in that the short fuel unit (3) is provided around its circumference with fuel rods with fresh heavy-water fuel (23, 24, 27, 28, 29).
5. A fuel assembly for a nuclear heavy-water reactor, comprising a plurality of fuel rods (4, 26), which are at least partially burnt-out in a light-water reactor, characterized in that the fuel rods (4, 26) are of the type which have been arranged between two end plates (5, 6) in a short fuel unit (3), in which several fuel units are arranged stacked on top of each other forming a fuel assembly for the light-water reactor.
6. A fuel assembly according to claim 5, characterized in that the fuel rods (4, 26) are arranged in the fuel unit (3), the fuel unit being arranged surrounded by fuel rods with fresh heavy-water fuel (23, 24, 27, 28, 29).
7. A fuel assembly according to claim 5 or 6, characterized in that the fuel rods (4, 26) are arranged in a polar lattice.
8. A fuel assembly according to claim 5 or 6, characterized in that the fuel rods (4, 26) are arranged in a square lattice.
9. A fuel assembly according to any of claims 5-8, characterized in that it comprises a spacer for positioning the fuel rods.
10. A fuel assembly according to any of claims 5-8, characterized in that it comprises two fuel units (3).
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE9703580A SE9703580L (en) | 1997-10-01 | 1997-10-01 | Process for reworking spent nuclear fuel from a light water reactor and fuel cartridge for a heavy water reactor |
| SE9703580-2 | 1997-10-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2246064A1 true CA2246064A1 (en) | 1999-04-01 |
Family
ID=20408473
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002246064A Abandoned CA2246064A1 (en) | 1997-10-01 | 1998-09-30 | Fuel assembly for heavy-water moderated nuclear reactor |
Country Status (3)
| Country | Link |
|---|---|
| KR (1) | KR19990036774A (en) |
| CA (1) | CA2246064A1 (en) |
| SE (1) | SE9703580L (en) |
-
1997
- 1997-10-01 SE SE9703580A patent/SE9703580L/en not_active Application Discontinuation
-
1998
- 1998-09-30 CA CA002246064A patent/CA2246064A1/en not_active Abandoned
- 1998-10-01 KR KR1019980041416A patent/KR19990036774A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| KR19990036774A (en) | 1999-05-25 |
| SE9703580L (en) | 1999-04-02 |
| SE9703580D0 (en) | 1997-10-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |