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
  • G21C3/336—Spacer elements for fuel rods in the bundle
• • 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 nuclear fuel assembly of pressurized-water type comprising a plurality of fuel units, each comprising fuel rods extending between a top nozzle and a bottom nozzle.
• the fuel exists in the form of fuel rods, each of which contains a stack of pellets of a nuclear fuel arranged in a cladding tube, a column of extruded fuel cylinders or an uninter ⁇ rupted column of vibration-compacted powdered fuel.
• the cladding tube is normally made of a zirconium-base alloy.
• a fuel bundle comprises a plurality of fuel rods arranged m parallel with each other in a certain definite, normally symmetrical pattern, a so-called lattice. The fuel rods are retained at the top by a top nozzle and at the bottom by a bottom nozzle.
• a fuel assembly comprises one or more fuel bundles, each one extending along the main part of the length of the fuel assembly.
• a fuel assembly is arranged in a core.
• the core is immersed in water which serves both as coolant and as neutron moderator.
• water serves both as coolant and as neutron moderator.
• the water flows from below and upwards through the fuel assembly, whereby the temperature of the water increases the higher it rises in the fuel assembly but it does not boil .
• the corrosion of the cladding tubes increases in the upper part compared with the lower part of the fuel assembly. This difference between the upper and lower parts gives rise to special factors which must be taken into consideration when designing the fuel assembly.
• UK 1 403 491 shows a fuel assembly for a pressurized-water reactor with a possibility of designing the upper part so as to differ from the lower part.
• This fuel assembly comprises a plurality of fuel units stacked on top of each other, each comprising a plurality of fuel rods extending between a top nozzle and a bottom nozzle.
• the fuel units are fixed to a centrally arranged support tube such that the bottom nozzle of one of the fuel units rests on the top nozzle of an adjacently located fuel unit and such that all the fuel rods in the fuel units are parallel to each other.
• the support tube extends through the whole fuel assembly and the fuel assembly has a substantially circular cross section.
• This fuel assembly is intended to be used in a nuclear reactor moderated by heavy water where the fuel assemblies are arranged in vertical pressure channels
• the spacer In the event of an earthquake, the spacer is subjected to great lateral forces.
• the lateral forces cause the fuel rods to be pressed against the spacers in adjacently located fuel assemblies.
• the lateral force which arises when the fuel rod is pressed against the wall of the cell is transmitted to the adjacent cell which, in turn, superimposes the lateral force on an adjacent cell etc.
• This superimposition of lateral forces may result in one or more cells at the corners of the spacer, where the superimposed force is greatest, collapsing.
• the collapse means that the function of the spacer is jeopardized, that is, keeping the indivi- dual fuel rods at a distance from each other to ensure that the whole geometry is capable of cooling to avoid super ⁇ heating.
• the object of the present invention is to provide a fuel assembly for a pressurized-water reactor comprising a plurality of short fuel units and members for absorption of forces, in particular lateral forces, which influence the fuel assembly such that a certain distance is maintained between the fuel rods.
• the present invention relates to a fuel assembly for a pressurized-water reactor comprising a fuel assembly with a plurality of fuel units, each comprising fuel rods extending between a top nozzle and a bottom nozzle.
• the features which characterize this fuel assembly are stated in claim 1.
• the fuel units have a substantially square cross section and comprise bottom and top nozzles which may be identically designed.
• the bottom nozzles and the top nozzles are provided with support lugs between the fuel rod positions.
• the task of the support lugs is to take up lateral forces which, during an earth ⁇ quake, may influence the top and bottom nozzles in order thus to ensure that a certain distance is maintained between the fuel rods .
• the support lugs may be achieved in the top and bottom nozzles by milling out recesses, holes, therein at fuel rod positions for the insertion of fuel rods into these.
• top and bottom nozzles are provided with flow openings to allow flow of the coolant flowing upwards through the assembly. The flow openings are arranged between the positions of the fuel rods. The support lugs are thus formed between the fuel rods and the flow openings.
• the top nozzles and bottom nozzles are preferably made in a zirconium alloy.
• the upper and lower ends, respectively, of the fuel rods which are attached to a top nozzle and a bottom nozzle, respectively, may be designed with radially upwardly extending vertical flanges such that flanges in two adjacently arranged fuel rods are adapted to make tight contact with each other, thus ensuring that a certain distance is maintained between the fuel rods.
• the fuel rods are fixed to the top and bottom nozzles, respectively, by means of, for example, laser welding or resistance welding.
• the advantage of the fuel assembly according to the invention is that, because of the short fuel units, a very stable construction may be obtained which, in a simple way, may be equipped with means for taking up lateral forces which influence the fuel assembly and which ensure that a certain distance is maintained between the fuel rods .
• Another advantage of the invention is that strong and axially extended structures for taking up lateral forces are avoided. Further, extra structures in the fuel assembly are avoided, the task of which is to take up the lateral forces; cf. , e.g. SE 94020757, where a reinforcement part is arranged as a complement to a sleeve-type spacer.
• a reinforcement part is arranged as a complement to a sleeve-type spacer.
• Still another advantage of the invention is that the absorption of forces occurs via the solid support lugs. Consequently, considerably greater forces may be taken up than in, for example, those cases where the fuel rods constitute the force-absorbing member.
• Figure 1 shows in a vertical section a fuel assembly of a pressurized-water type with short fuel units.
• Figure 2a shows in a vertical section A-A in Figure 2b fuel rods arranged in a top nozzle in a fuel unit, where the top nozzle is provided with support lugs between the fuel rods.
• Figure 2b shows the fuel unit in Figure 2a in a view from above.
• Figure 3a shows in a vertical section B-B in Figure 3b a fuel unit with four adjacently located fuel rods, each with an upper end which is provided with vertical flanges extending radially outwardly.
• Figure 3b shows the fuel unit in Figure 3a in a view from above.
• FIG. 1 shows a fuel assembly of a pressurized-water type of substantially square cross section, comprising a plura- lity of fuel units 3 stacked one above the other.
• Each fuel unit 3 comprises a plurality of fuel rods 4 arranged in parallel and in spaced relationship to each other in a given lattice. Further, each fuel unit 3 comprises a top nozzle 6 and a bottom nozzle 5 for attachment of the fuel rods 4 in their respective positions in the lattice.
• the fuel units 3 are stacked on top of each other in the longitudinal direc ⁇ tion of the fuel assembly and they are stacked in such a way that the top nozzle 6 in one fuel unit 3 is facing the bottom nozzle 5 in the next fuel unit 3 in the stack and such that the fuel rods 4 in all the fuel units 3 are parallel to one another.
• a fuel rod 4 comprises fissionable material in the form of a stack of fuel pellets 7b of uranium arranged in a cladding tube 7a.
• a coolant is adapted to flow from below and up through the fuel assembly.
• a number of so-called control rod guide tubes 4a are arranged extending through the whole fuel assembly.
• the control rod guide tubes 4a are intended to receive finger-shaped control rods (not shown) which are, respectively, inserted into and withdrawn from the guide tubes 4a for the purpose of con ⁇ trolling the power of the nuclear reactor.
• the guide tubes extend between a top part 4b and a bottom part 4c.
• the top part 4b is arranged above the uppermost fuel unit 3 in the fuel assembly and the bottom part 4c is arranged below the lowermost fuel unit 3 in the fuel assembly.
• the fuel units 3 are kept in position by being fitted onto and fixed to the control rod guide tubes 4a.
• top nozzle 6 The attachment of the fuel rods 4 to a top nozzle 6 is shown more clearly in Figure 2a.
• the top nozzle 6 is provided with support lugs 8 arranged between the fuel rods 4 which are attached thereto.
• the shape of the support lugs 8 is shown further clear from Figure 2b.
• Figure 2b also shows that the top nozzle 6 is provided with flow openings 9 for the passage of the coolant which, during operation of the reactor, flows from below and up through the fuel assembly. These flow openings 9 are thus arranged substantially between the positions of the fuel rods 4.
• the flow openings 9 may be provided with mixing vanes (not shown) by the arrangement of tabs in the edge of the flow opening in such a way that the coolant flowing through these is mixed.
• the support lugs 8 are achieved by the arrangement of recesses, holes, 11 in a plane plate.
• the holes 11 are arranged between the flow openings 9 and have such a depth that the material remaining in the bottom of the hole 11 is given a thickness of the order of size of 0.7 millimetres.
• the fuel rods 4, the upper ends of which are arranged in the holes 11, are given a possibility of diffe ⁇ rential growth by allowing the material in the bottom of the hole 11 to be deformed to a certain extent.
• the upper ends of the fuel rods are fixed to the top nozzle 6, for example by means of laser welding or resistance welding (se reference numeral 12 in Figure 2a) .
• the support lugs 8 are arranged between the fuel rods 4 and the flow openings 9.
• the support lugs 8 have a thickness in the axial direc ⁇ tion of the fuel rod of the order of size of 5 millimetres and are arranged such that each fuel rod is surrounded by four support lugs 8.
• the upper ends of the fuel rods 4 are shown with a somewhat rounded shape. The rounded shape further facilitates the differential growth of the fuel rods and deformation of the bottom of the hole 11.
• a side support 13 is shown, which is arranged welded or soldered to the top nozzle 6.
• the top nozzle 6 is provided with a support lug 8 also between the side support 13 and the adjacently located fuel rod 4 . In this way, a strong structure is obtained, with the ability of taking up lateral forces from adjacently arranged fuel assemblies .
• the top nozzle 6 is arranged fixed, permanently or detach- ably, to guided to the guide tube 4a via a sleeve 10.
• Figure 3a shows an alternative embodiment of support lugs 8 arranged in a fuel unit 3.
• the support lugs 8 are arranged in the upper part of a fuel rod 4, more particularly in the top plug which is adapted to seal the fuel rod.
• the support lugs 8 are designed extending outwards from the outer sur ⁇ face of the fuel rod 4 in a direction across the direction of flow of the coolant and in a direction parallel to the centre axis of the fuel rod.
• the support lugs 8 are four in number and evenly distributed around the top plug of the fuel rod 4.
• the support lugs 8 in adjacently located fuel rod 4 are adapted to make tight contact, in four directions, with each other in the fuel unit 3 or with a side support 13 surrounding the fuel unit 3. With this design of the upper end of the fuel rod 4, very good protection is obtained against the effect of lateral forces from, for example, fuel units located adjacent to this fuel unit.
• the fuel rods 4 in Figure 3a are arranged attached to the top nozzle 6 by arranging pins 14 in the respective ends thereof and inserting these pins into openings in the top nozzle 6.
• the above-mentioned side support 13 is shown, which is arranged integrated into the top nozzle and folded through an angle of the order of magnitude of 90° in relation to the rest of the structure of the top nozzle 6.
• the fuel rod 4 arranged adjacent to the side support 13 is provided with a support lug 8 which rests against the fuel rod.
• Figure 3b shows, in a view from above, part of a fuel unit comprising support lugs 8 according to Figure 3a.
• top nozzles 6 and upper ends of fuel rods 4 are discussed. It is, of course, possible or even advantageous to design bottom nozzles 5 and lower ends of fuel rods 4 in a manner corre ⁇ sponding to that described above.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Monitoring And Testing Of Nuclear Reactors (AREA)
• Liquid Carbonaceous Fuels (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20403101

Family Applications (1)

Country Status (3)

Cited By (1)

Citations (2)

• 1996
  • 1996-06-20 SE SE9602454A patent/SE511455C2/sv not_active IP Right Cessation
• 1997
  • 1997-06-18 EP EP97928610A patent/EP0906624A1/en not_active Withdrawn
  • 1997-06-18 WO PCT/SE1997/001083 patent/WO1997049093A1/en not_active Application Discontinuation

Patent Citations (2)

Non-Patent Citations (1)

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