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
• • 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 invention relates to a fuel assembly for nuclear reactors with a bundle of fuel rods held together by spacers, which is arranged between an end piece in the head and foot of the fuel assembly.
• the end pieces are formed by laterally open frames which carry a base plate or cover plate with through-openings for the coolant flow which is guided along the fuel rods.
• the two end pieces of a fuel assembly are attached to the ends of guide tubes into which control rods are inserted by drives, which are also attached to the reactor structure, and the position of which is also determined thereby.
• Grid-shaped spacers are also attached to the guide tubes, which combine the fuel rods into bundles and define their lateral spacing.
• these spacers have support elements (for example knobs and springs) to laterally support the fuel rods sitting in the mesh of the grids, but in addition to such support grids, mixing grids can also be used which only define a minimum distance between the fuel rods , but otherwise carry flow control surfaces or other mixing elements in order to increase the cooling effect by swirling and mixing the coolant.
• support elements for example knobs and springs
• mixing grids can also be used which only define a minimum distance between the fuel rods , but otherwise carry flow control surfaces or other mixing elements in order to increase the cooling effect by swirling and mixing the coolant.
• Water which is also required as a moderator, serves as the coolant in order to generate from the energy-rich neutrons released during the nuclear reaction the amount of moderated ("thermal") neutrons necessary for maintaining the nuclear reaction.
• thermal neutrons necessary for maintaining the nuclear reaction.
• the fuel / coolant ratio in the reactor core has mostly been regarded as sufficiently homogeneous, since the coolant affects the space between the fuel rods of the fuel elements, the narrow gap between the fuel elements themselves and the interior of the guide tubes (provided that it is not displaced there by control rods) is distributed.
• the "skeleton construction" is customary for pressurized water fuel elements, in which the end pieces, guide tubes and spacers form the supporting skeleton for holding the fuel rod bundle.
• Such a skeleton construction is described in EP-A 0 146 896, in which a part of the spacers is designed as a partial mixing grid, since it extends only over a part of the fuel element cross-section in order to have a particularly high cooling effect Increase parts of the fuel assembly.
• the possibility is described of assembling the fuel rod bundle from partial bundles of fuel rods of different thicknesses, each of these bundles requiring partial spacers, the mesh of which is adapted to the respective size of the fuel rods.
• Boiling water fuel elements differ from pressurized water fuel elements insofar as they do not use control rods distributed over the fuel element cross section, but rather the control elements carried by the reactor structure are introduced into the water-filled column between adjacent fuel elements.
• the size of the fuel elements is determined by the reactor structure.
• the coolant is conducted in a funnel-shaped foot piece through the base plate and into the interior of a fuel element box which laterally surrounds the fuel bundle.
• the coolant largely evaporates on the fuel rods and is discharged as a water / steam mixture through the cover plate in the head piece.
• the foot piece and the head piece are connected to one another by "support rods" (i.e. fuel rods fastened with their ends to the base plate and cover plate), whereby these support rods.
• Support rods also carry the spacers. With this "integra- 3 len construction "so fuel rods are integrated into the support structure of the fuel assembly.
• the fuel elements are partially inspected (possibly repaired) after an operating cycle (e.g. 12 or 18 months) and moved to other positions in the reactor core, and sometimes replaced with new fuel elements with high reactivity. While the spent fuel bundle is replaced as a single assembly when the spent fuel elements are replaced, a defective fuel element may need to be inspected individually and, if necessary, individual fuel rods replaced. With the skeleton construction, the fuel rods are accessible from the side for inspection; since the integrity of the skeleton is not compromised as long as only one of the end pieces is dismantled, too a single fuel rod can be easily replaced in the direction of the dismantled end piece. After an operating cycle, the reactor therefore only has to be shut down for a short time in order to carry out such simple manipulations.
• an operating cycle e.g. 12 or 18 months
• the fuel rods have to be individually pulled out of the quiver for their inspection - afterwards, depending on their condition, they can be placed in other positions within the fuel assembly.
• loading plans are drawn up after each operating cycle, according to which, like the stones of a mosaic, such fresh, partially poisoned fuel elements and fuel elements, which have only partially burned off and are removed from the old loading of the core, over the reactor core be distributed.
• the size of these "mosaic stones” is determined by the size of the fuel elements specified by the reactor structure. The pause in operation of the reactor necessary for moving the fuel elements affects the economy of the reactor, so that the largest possible "mosaic stones", i.e. a division of the fuel rods into the largest possible bundle, each grouped together by a fuel assembly, is desirable.
• the size of the fuel assemblies can only be changed by changing the structures of the core (the cover of the reactor pressure vessel on which the controls for the controls are located; the guides for the controls; the grids and scaffolds that support the fuel assemblies; as well as in the fuel store of the reactor).
• Such changes are extremely complex - if only because the mass of the resulting replaced components and other waste is difficult to dispose of.
• the invention is therefore based on the object of disassembling the fuel rods of a nuclear reactor into fuel rod bundles or fuel elements in such a way that, without changes to the reactor structure and without excessive manipulation of the fuel rods and long periods of non-operation, flexible, adapted to the particular requirements Distribution of the fuel over the cross section of the reactor core is possible.
• the invention therefore creates a fuel assembly that can be handled as a unitary assembly, for example to lift it out of the reactor core and to transport it to corresponding workstations.
• the fuel assembly is made up of several sub-assemblies in a modular manner, each sub-assembly being held together in one module and therefore forming a coherent component.
• modules with fresh, highly enriched partial bundles with complementary modules made up of partially spent fuel elements can be put together to form new fuel elements whose enrichment is within narrow limits corresponds in each case to the value which is necessary for the position which the corresponding fuel element is to assume in the core in the next cycle.
• the invention therefore provides in a first embodiment a fuel assembly, each having an end piece in the foot and in the head of the fuel assembly and an intermediate bundle of rods, some of which e.g. can be designed as a control rod guide tube or water pipes, but are predominantly designed as fuel rods.
• Spacers are fastened to a support structure of the fuel assembly (e.g. the control rod guide tubes or water tubes) between the head and foot at a vertical distance from one another and hold the rods in positions which are practically uniformly distributed over the cross section of the fuel assembly in the respective spacer level.
• some rods of the bundle form a central sub-bundle which is arranged around the fuel assembly axis and which is surrounded on all sides by the remaining rods of the bundle.
• the rods of the bundle sit in the mesh of a central part spacer in each spacer level, which is independent of the remaining parts of the corresponding spacer.
• Partial bundles, the central part spacer and a corresponding support structure for holding it form a central module that can be removed as a coherent component from the fuel assembly.
• the fuel assembly also contains other parts, for example the other fuel rods and their partial parts. stand with the corresponding support elements, the end pieces in the head and foot of the fuel assembly or at least corresponding partial end pieces, and possibly a fuel assembly box.
• the central module is assembled with these remaining parts of the fuel assembly so that all parts of the fuel assembly can be used and removed together as a coherent assembly in the core of the nuclear reactor. This central module can be inserted into the fuel assembly in at least four different positions with respect to the remaining parts of the fuel assembly.
• the invention insofar as the invention relates to a reactor with control rods which are introduced into control rod guide tubes of fuel elements, the invention also provides a fuel element with an end piece in each case in the head and foot of the fuel element and a bundle of fuel rods of the same diameter and guide tubes arranged in between. as well as several spacers held between the head and foot at a vertical distance from one another on the guide tubes, which keep the fuel rods and guide tubes in positions which are practically uniformly distributed over the cross section of the fuel assembly.
• the fuel rods and guide tubes of the bundle are divided into partial bundles and the spacers consist of partial spacers which correspond to the fuel rods of the partial bundles.
• a partial bundle and at least its partial spacers form a module which can be removed from the fuel assembly as a coherent component.
• All modules of the fuel assembly are composed in such a way that all parts of the fuel assembly can be inserted and removed together as a coherent assembly in the core of the reactor, the fuel assembly modules being able to be assembled in at least four different positions without the outer dimensions or the driver's staff positions Change fuel element.
• the fuel assembly remains as a unitary assembly, which is predetermined within the core by the outer dimensions of the previous fuel assemblies and is used or removed as a unitary assembly.
• the fuel element can, however, be broken down into individual sub-bundles ("modules") by simple manipulations, a desired average enrichment being compiled from differently enriched or burned-off sub-bundles according to the modular system.
• modules sub-bundles
• fresh, highly enriched sub-bundles can be put together with partially burned-off fuel rods arranged in complementary parts of the fuel element in order to set the enrichment within relatively narrow limits that is necessary in the core in the next cycle at the position determined for the fuel element in question is.
• FIG. 1 shows the division of the fuel assembly cross section into two modules
• FIG. 2 shows a schematic longitudinal section through the fuel assembly of FIG. 1
• IG 3 shows a division of the fuel assembly into three concentric modules
• IG 4 shows a schematic longitudinal section through the fuel assembly.
• element according to FIG. 3 IG 5 a division of the square bundle of rods into four square modules
• IG 6 a schematic longitudinal section through the fuel element according to FIG. 5
• IG 7 a base plate in the foot of the fuel element according to FIG. 6, 8 shows another base plate in the base of a fuel assembly according to FIG. 6,
• FIG. 10 shows the end pieces of several fuel assemblies according to FIG. 5, which sit side by side in the reactor core, and
• FIG. 11 shows the spacers of fuel assemblies, which are designed similar to FIG. 9 and sit next to one another in the reactor core.
• FIG. 1 The cross section shown in FIG. 1 through the fuel assembly in the plane of a spacer shows that the webs 1 of the spacer form square meshes 2, each of which contains a fuel rod (or omitted here) or a guide tube 3 for receiving a control rod.
• the fuel rods all have the same diameter and are interchangeable, while the guide tubes are somewhat thicker and practically rest on the webs of the spacer.
• This spacer grid is divided into two parts, namely a central part 4 with a corresponding part spacer which is fastened to the first guide tubes 3 'and an outer part spacer 5 which is fastened to the guide tubes 3 1 'is attached.
• FIG. 2 shows that the central partial spacers 6 are held on the guide tubes 3 'by corresponding sleeves 7 welded in their mesh and together with a central module end piece 9 in the fuel element foot F and a corresponding one central module end piece 10 in the head H of the fuel assembly form a support structure for the central module I in which the fuel rods (not shown) of the central sub-bundle are seated.
• the module end piece 10 in the head H is supported on the rest 12 of the fuel assembly head H via a laterally projecting flange 11. This central module therefore hangs downwards in the center of the fuel assembly, so that when its guide tubes expand, the other mode dul end piece 9 in the foot of the fuel assembly can move relative to the corresponding rest 13 of the fuel assembly foot F.
• the rods (not shown) surrounding the central module form in this case, in which the rods of the fuel assembly are broken down into only two sub-bundles, a further module II, each with a partial spacer 8 in each spacer plane, the guide tubes 3 " wear these partial spacers 8 and wear them on the corresponding remaining end pieces 12 and 13 in the head and foot of the fuel assembly.
• This construction enables e.g. to combine a central module, the energy content of which is sufficient for a further operating cycle in the reactor core, with a complementary module, which is provided with fresh, highly active fuel rods, or to exchange the modules of different fuel elements with one another.
• the orientation of the central module in relation to the position of the complementary module can also be freely specified. While in FIG. 1 the corners A, B, C, D of the fuel assembly or of the outer module each face the corners a, b, c, d of the central module, arrangements can also be selected in which e.g. the outer corner A faces the corner b, c or d. This makes it e.g. also possible in the case of a fuel assembly whose guide tubes 3 ', 3' * e.g.
• the end piece F in the foot of the fuel assembly in this construction consists of a frame that is open at the bottom and through the coolant in the direction of the arrows shown flows to a base plate, which covers the fuel assembly down and consists of the lower module end piece 9 and a corresponding residual base plate 9 '.
• a base plate which covers the fuel assembly down and consists of the lower module end piece 9 and a corresponding residual base plate 9 '.
• the coolant penetrates into the fuel element so that it emerges again through corresponding (not shown) passage openings in a cover plate.
• This cover plate in turn consists of the upper module end piece 10 and the remaining cover plate 10 ', which is held in a subsequent frame open at the top.
• This construction of the end pieces in the foot F and head H of the fuel assembly corresponds (with the exception of the division of the base plate and cover plate) to the usual structure of pressurized water fuel elements.
• the lower and upper rod holding plates in the foot and head can also be of conventional types Boiling water fuel elements are divided in order to remove the fuel assembly from the core as a whole assembly for replacing the fuel rods and / or displacing the fuel elements, but in each case to be able to handle the partial bundles of the rods as individual components without the fuel rods having to pull them all out of the fuel assembly skeleton.
• the rods surrounding the central module can also be divided into several further modules which are arranged concentrically to one another and to the central module; According to FIG. 9, however, the further rods can also be divided into several modules which are arranged next to one another in order to form a ring which is concentric with the central module.
• the fuel rods are also removed from the spacer grid in FIG. 3 to simplify the illustration, so that only the webs of the spacer and their mounting on the guide tubes of the fuel assembly are shown.
• the fuel assembly accordingly contains an end piece in the base and head of the fuel assembly and an intermediate bundle of fuel rods of the same diameter and the guide tubes 23 ', 23' '.
• These fuel rods and guide tubes are thus arranged at a vertical distance from one another in a plurality of spacer planes with a vertical distance from one another between the head and foot and hold the fuel rods and guide tubes at positions which are practically uniformly distributed over the cross section.
• the spacers of the fuel assembly are each divided into a central partial spacer 20 belonging to a first partial bundle, a second partial spacer 21 and a further partial spacer 22, around the fuel rods and guide tubes of the bundle in corresponding partial bundles summarize.
• the first sub-bundle also contains the associated guide tubes 23, to which the central sub-spacer 20 is attached, while the sub-spacer 21 is held by the guide tubes 24.
• No guide tube is available for the partial spacer 22, which in this case comprises the two outermost columns and rows of the fuel rods. on certain fuel rods 25, which (as is usual with boiling water fuel elements) are designed as supporting rods.
• These individual modules can thus be exchanged for corresponding modules of other identical fuel elements, whereby the modules can be put together in several different positions while maintaining their external dimensions and the guide tube positions predetermined by the positions of the control rods.
• the central first module I also includes a module foot piece 29 and a module head piece 30, which are fastened to the guide tubes 23 of the central first module.
• the foot F of the firing is broken down into the frame 33 with the partial base plate 29 'on the one hand, the partial base plate 29 on the other hand, and a frame part 26, these three parts each having a partial base piece assigned to the corresponding module form.
• a corresponding disassembly is also provided for the frame 32, the partial cover plates 30, 30 'and a corresponding frame 27 in the head H of the fuel assembly.
• the central first module is supported with its head end piece 30 on the corresponding head end piece 30 ', 32 of the second module II', so that the module foot piece 29 of this central module has an axial extension the bundle is axially displaceable relative to the module end piece 33, 29 'of the second module.
• the entire fuel assembly or even its central module can be lifted up out of the assembly, in which the fuel assemblies are arranged close together in the core. If the screw connections or fastenings 31 with which the guide tubes 24 are screwed to the partial base plate 29 'or the partial head parts 30' are loosened, the foot part 33 can be removed, for example, the outer module with the spacers 22 now being removed becomes accessible and can be replaced.
• the frame part 26 can to the to fix the outer module with its spacers 22 in the fuel assembly, to be attached to the foot part 33, but it can also be carried by the supporting rods 25 and engage in a corresponding counter profile of the frame 33.
• the rods of the bundle lying on the edge can thus form a single, ring-shaped module III.
• a concentric ring can, however, also be formed by several modules lying next to one another.
• the weight of the central module over the part cover plate 10 'or 30' belonging to the second module is on the frame 12 or 32 when the fuel element is lifted and over the guide tubes 3 'or 24 on the corresponding partial base plate 9 'or 29' of the frame 13 or 33 'on the frame 13 or 33 if the fuel element is placed on a corresponding supporting structure in the core with its foot.
• Guide tubes for pressurized water fuel assemblies generally contain damping elements to absorb axial shocks. These damping members are not required for the guide tubes 3 'or 23 of the central module or can be made weak, while the guide tubes of the second module are damped correspondingly more to keep mechanical loads on the guide tubes 3' 'and 24 low.
• the construction of the individual modules Ia, Ib, Ic, Id is desirable.
• one quadrant can be replaced individually with a new module or a corresponding quadrant of another fuel element, the inner corners a, b, c and d of the fuel element being able to abut one another in this order, that is to say the inner corner a of the module Ia is always arranged diametrically opposite to the outer corner A of the entire fuel assembly.
• the fuel elements can also be oriented in a different way, for example by combining modules Ia and Ib with one another. are exchanged so that the inner corner b of the module Ib is diametrically opposite the outer corner A of the fuel assembly without the modules Ic and Id being displaced. Corresponding exchanges can also be made between other modules.
• the end pieces are in the head and foot of the fuel assembly Element exposed to less severe exposure to radiation, corrosion and heat flows and can also be made much more stable.
• these end pieces can e.g. be made of steel, while the spacers are preferably made of Zircaloy in the interest of low neutron absorption. If the fuel rods have burned down, the spacers have usually reached the end of their service life and would have to be replaced together with the fuel rods and disposed of. For the end pieces of the fuel assembly, however, the service life is not limited by such factors, and they can therefore be used repeatedly.
• the fuel assembly is constructed in such a way that the end pieces do not contain any parts of the modules, ie the modules can be moved or replaced as separate components after the head and foot sections have been removed.
• each module fuel rods combined to form a partial bundle are combined by the partial spacers 50, 51 to form the individual modules, while the guide tubes 53, 54 of these modules are each attached to the multiple used Bare end pieces 57, 58 are releasably attached in the head and foot of the fuel assembly.
• FIG. 7 shows the normal design of the base plate 58 of such an end piece in the fuel element foot, wherein in addition to the fastening elements 56, which are each located at the position of a guide tube, corresponding passage openings 59 for the coolant flow can also be seen.
• the modules Ia ... Id can be arranged in the manner shown in FIG. 5, the inner corners a, b, c, d of each module always remaining inner corners. This is necessary if the fuel assembly with the end pieces according to FIG. 7 is used at positions in the core at which the core structure also provides corresponding control rods that are to be inserted into the guide tubes of the fuel assembly.
• end pieces according to FIG. 8 can therefore be provided at such positions, i.e. the modules Ia ... Id of FIG 5 can now be arranged between the end pieces of FIG 8 such that the corners a, b, c, d are now no longer as the inner corner diametrically to the outer corners A, B, C and D. of the fuel element, but directly at these corners.
• the corner a of the module Ia there is then a position in which the corner a comes to lie on the outer corner A (FIG. 8) or another outer corner B, C and D.
• the bundle can also be used accordingly
• module I ' can also be used in four different positions relative to the position of the other modules IIa ... IId.
• the fuel assemblies sit closely together in the framework structure of the reactor core. If the heads and feet of the fuel assemblies are all of the same design and, as shown in FIG. 7, are provided with holders for the support structure (guide tube) of the fuel assembly skeletons, the fuel assemblies can be interchanged with one another as desired. 10, on the other hand, it is assumed that the fuel assembly 70, the end pieces of which correspond to FIG. 8, is located at a location where no control rods are inserted into the guide tubes, while the fuel assemblies 71 and 72, which correspond to FIGS. 5 and 6 are constructed, must accommodate control rods in the guide tubes 53, 54 at their position.
• the spacers are broken down along the edge of the fuel assembly into adjacent, identically constructed partial spacers VI, VII, VIII, IX.
• the corresponding modules can at least at least be exchanged cyclically. In this example, they are also arranged in a ring around an inner module with the central partial spacer V.
• FIG. 11 also shows the partial spacers VI ', VII', VIII ', IX' of adjacent fuel elements.
• the end pieces in the head and foot of the fuel assemblies can be the same for all fuel assemblies, but can also be designed in accordance with FIG. 10.
• a cluster of several fuel elements is also formed in the reactor core, which are constructed in such a way that a first fuel element (80) each has modules with partial spacers (for example VI, VII, VIII, IX) on the circumference sides of the fuel assembly.
• the end pieces of this first fuel element 80 and a second fuel element (81, 82) are designed such that these modules of the first fuel element are replaced with modules (VI 1 , VII ', VIII', IX 1 ) of the second fuel element and the sides of the modules which were arranged on the circumference in the first fuel element come to lie inside the second fuel element after being replaced.

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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)
• Structure Of Emergency Protection For Nuclear Reactors (AREA)

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Citations (6)

• 1995
  • 1995-08-29 TW TW084108984A patent/TW303470B/zh active
  • 1995-09-18 WO PCT/DE1995/001284 patent/WO1996010828A1/de active Application Filing
  • 1995-09-18 DE DE29520871U patent/DE29520871U1/de not_active Expired - Lifetime

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