GB2582804A

GB2582804A - Fuel handling

Info

Publication number: GB2582804A
Application number: GB1904726.5A
Authority: GB
Inventors: A Wilks Laura; J Maxwell Andrew
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2019-04-04
Filing date: 2019-04-04
Publication date: 2020-10-07
Anticipated expiration: 2039-04-04
Also published as: GB2582804B; GB201904726D0

Abstract

A fuel assembly shield (1) for protecting a fuel assembly during refuelling of a nuclear reactor comprises: an elongate shield structure (2) for surrounding the fuel assembly; and a closure (7) movable between an open configuration in which an end (4A) of the elongate shield structure (2) is open for insertion or removal of the fuel assembly and a closed configuration in which the end (4A) of the elongate shield structure (2) is closed for retention of the fuel assembly within the elongate shield structure (2). The shield (1) may comprise apertures enabling fluid flow through the shield (1). The closure (7) may be hinged. The shield (1) may comprise neutron absorbing material such as a metal alloy or boron, xenon, cadmium, hafnium, gadolinium, cobalt, samarium, titanium, dysprosium, erbium, europium, molybdenum or ytterbium. The method of refuelling using the shield (1) and a grab and crane is disclosed.

Description

FUEL HANDLING

Field of the Disclosure

The present disclosure concerns fuel assembly shields, fuel handling apparatus, and methods of transferring fuel assemblies between locations in a nuclear facility.

Background of the Disclosure

In certain types of nuclear reactor, such as in a pressurised water nuclear reactor (PWR), a nuclear reaction in the reactor core is sustained by fission of fissile material provided in nuclear fuel rods which are arranged in fuel assemblies, sometimes referred to as fuel bundles. In order to refuel the reactor core when the fissile material is depleted, it is necessary to lift irradiated fuel assemblies out of the reactor core and to transport these irradiated fuel assemblies through a containment building to a spent fuel area. Replacement fuel assemblies can then be installed in the reactor core. Spent fuel assemblies may also be transported to a reprocessing plant for reprocessing or to a storage facility for long-term storage.

Transportation of spent fuel assemblies between locations within a facility generally takes place underwater. The surrounding water cools the fuel assemblies and, in existing reactor designs, soluble boron dissolved in the water acts as a neutron absorber, providing criticality control in the event that a fuel assembly is dropped during transportation. However, there are difficulties associated with the disposal of water contaminated with soluble boron and the provision of alternative criticality control mechanisms would therefore be desirable.

Summary of the Disclosure

According to a first aspect, there is provided a fuel assembly shield for protecting a fuel assembly during refuelling of a nuclear reactor, the fuel assembly shield comprising: an elongate shield structure for surrounding the fuel assembly; and a closure movable between an open configuration in which an end of the elongate shield structure is open for insertion or removal of the fuel assembly and a closed configuration in which the end of the elongate shield structure is closed for retention of the fuel assembly within the elongate shield structure.

It will be appreciated that a fuel assembly generally comprises an arrangement of fuel rods. Each fuel rod may contain nuclear fuel (i.e. fissile material, such as enriched uranium dioxide), for example in the form of nuclear fuel pellets. The exterior of each fuel rod may be formed by a metal tube, for example a metal tube formed from a corrosion-resistant metal such as a zirconium alloy. The metal tube may be back-filled with helium gas. Each fuel rod may be substantially cylindrical. Each fuel rod may have a diameter of about 1 cm. The fuel assembly may comprise a plurality of said fuel rods carried by a support. The fuel assembly may comprise more than 100, for example, around 200 to around 300, fuel rods arranged on the support.

The fuel assembly may be elongate. The fuel assembly may be substantially cuboid in shape. For example, the fuel assembly may have a substantially rectangular, e.g. square, shape in cross-section perpendicular to a longitudinal axis thereof. The fuel assembly may have a substantially square shape in cross-section perpendicular to the longitudinal axis and the fuel rods may be arranged in, for example, a 14 x 14, 15 x 15, 16 x 16 or 17 x 17 array (as typically used in pressurised water reactors (PWRs)). The fuel assembly may be about 5 m long and the substantially square cross-section may have a side length of about 20 cm. However, alternative cross-sectional shapes and/or fuel rod arrangements are possible. For example, the fuel assembly may have a substantially hexagonal shape in cross-section perpendicular to the longitudinal axis (as typically used in water-water energetic reactors (VVWERs/VVERs)).

The fuel rods in the fuel assembly may be spaced apart from one another. An interior of the fuel assembly may be hollow, i.e. devoid of fuel rods.

The elongate shield structure may have first and second ends. That is to say, the elongate shield structure may extend (i.e. along a longitudinal axis) between the first and second ends. The elongate shield structure may be elongate along the longitudinal axis between the first and second ends.

The closure may be provided at the first end. The elongate shield structure may further have an opening at the second end, for example for insertion or removal of a fuel handling grab. The elongate shield structure may therefore be substantially hollow.

The elongate shield structure, or an interior space thereof, may be substantially cuboidal in shape. The elongate shield structure, or the interior space thereof, may have a substantially square shape in cross-section perpendicular to the longitudinal axis of the elongate shield structure. The elongate shield structure, or the interior space thereof, may be no less than about 3 metres, no less than about 4 metres, or no less than about 5 metres, in length. The substantially square cross-section may have a side length of no less than about 10 cm, for example, no less than about 20 cm. A substantially cuboidal elongate shield structure or interior space may be suitable for use with substantially cuboidal fuel assemblies as used in PWRs. However, it will be appreciated that other elongate shield structure and/or interior space shapes and/or dimensions are possible. For example, an elongate shield structure, or an interior space thereof, having a substantially hexagonal shape in cross-section perpendicular to the longitudinal axis may be suitable for use with substantially hexagonal fuel assemblies as used in VVVVERsNVERs. Further alternatively, the elongate shield structure, or an interior space thereof, may be substantially cylindrical (i.e. having a substantially circular shape in cross-section perpendicular to the longitudinal axis).

The elongate shield structure may have one or more side walls, wherein a side wall of the elongate shield structure is a wall which extends between the first and second ends, generally parallel to the longitudinal axis. For example, where the elongate shield structure is substantially cylindrical, it may be that the elongate shield structure has a single side wall which extends around the circumference of the substantially circular cross-section. Where the elongate shield structure is substantially cuboidal, the elongate shield structure may have four side walls. Where the elongate shield structure is substantially hexagonal in cross-section, the elongate shield structure may have six side walls.

The elongate shield structure may comprise a plurality of apertures, for example to enable circulation of fluid (such as water) around the fuel assembly when enclosed therein. For example, it may be that the elongate shield structure is a cage.

The plurality of apertures may be provided on one or more side walls of the elongate shield structure. The plurality of apertures may be provided on the majority (e.g. all) of the side walls of the elongate shield structure. The plurality of apertures may extend across at least 10 %, for example, at least 25 %, or at least 50 %, of an external surface area of the elongate shield structure (where it will be appreciated that the external surface area of the elongate shield structure is the notional external surface area of the elongate shield structure (e.g. of the side walls) which would be measured if the apertures in the elongate shield structure were filled with solid material).

The apertures may be of any shape. For example, the apertures may be circular, rectangular (e.g. square) or hexagonal in shape. The apertures may be configured (e.g. shaped, dimensioned and/or arranged) so as to permit flow of fluid (such as water) between the interior of the elongate shield structure and the exterior of the elongate shield structure when a fuel assembly is retained within the elongate shield structure. For example, the apertures may have a characteristic dimension (e.g. a diameter, where the apertures are circular, or a side length, where the apertures are square) of no less than about 1 mm, for example, no less than about 1 cm, and no greater than about 10 cm, for example, no greater than about 5 cm.

The apertures may be formed as openings (e.g. perforations) in one or more substantially continuous pieces of material. For example, the apertures may be formed as openings (e.g. perforations) in one or more sheets of material (e.g. one or more sheets of metal) which form (e.g. side) walls of the elongate shield structure. Alternatively, the apertures may be spaces between strips, bars or wires of material which form (e.g. side) walls of the elongate shield structure. For example, one or more (e.g. side) walls of the elongate shield structure may comprise (e.g. be formed from) a mesh.

The elongate shield structure may have an opening at the first end for insertion and removal of the fuel assembly. It may be that, when the closure is in the open configuration, the opening at the first end is open for insertion or removal of the fuel assembly. It may be that, when the closure is in the closed configuration, the opening at the first end is closed for retention of the fuel assembly within the elongate shield structure. For example, it may be that, when the closure is in the closed configuration, one or more closing parts of the closure extend across at least part of the opening at the first end, thereby impeding movement of the fuel assembly into or out of the elongate shield structure, and when the closure is in the open configuration, the one or more closing parts are retracted for unimpeded insertion or removal of the fuel assembly from the elongate shield structure. It may be that the one or more closing parts of the closure extend across the majority, for example the entirety, of the opening at the first end when the closure is in the closed configuration.

The closure may be a hinged closure. For example, the one or more closing parts of the closure may be hingedly mounted to the elongate shield structure such that the one or more closing parts may be pivoted between the open and closed configurations. In some examples, the closure comprises first and second closing parts, each hingedly mounted to opposing sides of the opening at the first end such that the first and second closing parts are pivotable between the open configuration, in which the first and second closing parts are retracted from the opening for insertion or removal of the fuel assembly, and the closed configuration, in which the first and second closing parts extend across at least part of the opening to impede insertion or removal of the fuel assembly. It may be that the first and second closing parts meet (e.g. abut or overlap) in the closed configuration. It may be that the majority (e.g. the entirety) of the opening is covered by the first and second closing parts in the closed configuration.

The skilled person will appreciate that other closure mechanisms are possible. For example, the closure may be a sliding closure in which the one or more closing parts of the closure are slidably mounted to the elongate shield structure to enable sliding of the one or more closing parts between the open and closed configurations. In some examples, the sliding closure comprises a slidable wall slidably mounted to the elongate shield structure to enable sliding of the slidable wall across the first end between the open and closed configurations.

The fuel assembly shield (e.g. the elongate shield structure and/or the closure) may comprise a neutron absorber. For example, the fuel assembly shield (e.g. the elongate shield structure and/or the closure) may comprise a material containing the neutron absorber, i.e. a neutron-absorbing material. It may be that the fuel assembly shield (e.g. the elongate shield structure and/or the closure) is formed (for example, in part, substantially, or entirely) from the material containing the neutron absorber (i.e. the neutron-absorbing material). Alternatively, it may be that the material containing the neutron absorber (i.e. the neutron-absorbing material) is provided as a coating on the fuel assembly shield (e.g. the elongate shield structure and/or the closure).

The neutron absorber may be an isotope (i.e. nuclide) having a thermal neutron capture cross-section greater than about 100 barn (i.e. greater than about 1 x 10-26 m2) and a negligible thermal neutron fission cross-section.

The neutron absorber may be selected from isotopes (i.e. nuclides) of: boron (B), xenon (Xe), cadmium (Cd), hafnium (Hf), gadolinium (Gd), cobalt (Co), samarium (Sm), titanium (Ti), dysprosium (Dy), erbium (Er), europium (Eu), molybdenum (Mo), ytterbium (Yb). The fuel assembly shield (e.g. the elongate shield structure and/or the closure) or the neutron-absorbing material may comprise more than one of said isotopes (i.e. nuclides). The skilled person will appreciate that many of these elements exhibit different isotopic (i.e. nuclide) forms and will select those isotopes (i.e. nuclides) which are neutron-absorbing (i.e. which have a thermal neutron capture cross-section greater than about 100 barn (i.e. greater than about 1 x 10.26 m2) and a negligible thermal neutron fission cross-section). For example, a neutron-absorbing isotope (i.e. nuclide) of boron (B) is boron-10 (10B).

It may be that the fuel assembly shield (e.g. the elongate shield structure and/or the closure) is formed (for example, in part, substantially, or entirely) from a metal. The metal may be an elemental metal or a metal alloy, where it will be appreciated that the term 'metal alloy' refers to a mixture of at least one elemental metal and one or more other metal or non-metal elements (referred to as 'alloying elements'), for example forming a solid solution and/or intermetallic compound. The or each neutron-absorber may be a component (i.e. alloying element) of the metal alloy.

The metal may be corrosion-resistant. For example, the fuel assembly shield (e.g. the elongate shield structure and/or the closure) may be formed (for example, in part, substantially, or entirely) from a stainless steel. The stainless steel may include the or each neutron-absorbed as an alloying element. For example, the stainless steel may be boronated (i.e. borated) stainless steel. Boronated stainless steel may contain no less than about 0.1 wt. %, for example, no less than about 0.2 wt. %, boron (B). An example boronated stainless steel contains about 18 wt. % chromium (Cr), about 12 wt. % nickel (Ni), and from about 0.1 wt. % to about 5 wt. %, for example, from about 0.2 wt. % to about 2.25 wt. %, boron (B), in addition to iron (Fe) and inevitable impurities. The boronated stainless steel may comply with ASTM standard A887.

Incorporation of a neutron absorber into the fuel assembly shield (e.g. the elongate shield structure and/or the closure) may reduce (e.g. eliminate) the need for adding a neutron absorber (such as soluble boron) to fluid (e.g. water) in a nuclear reactor.

According to a second aspect, there is provided fuel handling apparatus for use in refuelling a nuclear reactor, the fuel handling apparatus comprising: a fuel handling grab for gripping a grab end of a fuel assembly; a fuel assembly shield according to the first aspect; and an actuator for moving the closure between the open and closed configurations.

The actuator may comprise an actuating element coupled to a motor for driving movement of the actuating element. The actuating element may be coupled to the closure (e.g. to one or more closing parts of the closure) for moving the closure between the open and closed configurations. The skilled person will appreciate that any type of actuator known in the art may be used to drive movement of the closure between the open and closed configurations. For example, the actuator may be a linear actuator or a rotary actuator and may be hydraulic, pneumatic or electric.

The fuel handling apparatus may further comprise a crane. The fuel handling grab and the fuel assembly shield may be suspended from the crane. The crane may be operable to lower and raise the fuel handling grab and the fuel assembly shield, for example by way of a hoist or a telescopic mast. The crane may be a gantry crane, overhead crane or tower crane.

The fuel handling apparatus may further comprise a controller. The controller may be configured (e.g. programmed) to conduct lowering and raising operations for lowering and raising the fuel handling grab and/or the fuel assembly shield. The controller may be configured (e.g. programmed) to control movement of the closure between the open and closed configurations by operating the actuator. The controller may comprise one or more processors, e.g. one or more computers, in communication with a memory storing computer-executable program code containing instructions for carrying out lowering or raising operations or for controlling opening and closing of the closure.

The fuel handling grab and the fuel assembly shield may be suspended from the crane such that the fuel handling grab and the fuel assembly shield are each independently movable (for example, such that one of the fuel handling grab and the fuel assembly shield may be moved (e.g. lowered or raised) while the other of the fuel handling grab and the fuel assembly shield remains static or is moved in an opposing direction).

The fuel handling grab may be suspended from the crane by a telescopic handling mast. The fuel assembly shield may be suspended from the crane by a telescopic handling mast. The fuel handling grab and the fuel assembly shield may be suspended from the crane by the same telescopic handling mast. Alternatively, the fuel handling grab and the fuel assembly shield may be independently suspended from the crane by respective telescopic handling masts.

The controller may be configured (e.g. programmed) to permit or cause relative movement between the fuel handling grab and the fuel assembly shield. For example, the controller may be configured (e.g. programmed) to conduct a raising operation for raising the fuel handling grab while the fuel assembly shield is static, for example to draw a fuel assembly gripped by the fuel handling grab into the fuel assembly shield.

Additionally or alternatively, the controller may be configured (e.g. programmed) to conduct a lowering operation for lowering the fuel handling grab while the fuel assembly shield is static, for example to lower the fuel assembly gripped by the fuel handling grab out of the fuel assembly shield. It will be appreciated that the controller may configured (e.g. programmed) to conduct any combination of raising or lowering operations for raising or lowering the fuel handling grab and/or the fuel assembly shield as required for drawing a gripped fuel assembly into the fuel assembly shield, for transporting the gripped fuel assembly within the fuel assembly shield within a reactor containment area, and for lowering the gripped fuel assembly out of the fuel assembly shield.

It may be that the fuel handling grab and the fuel assembly shield are arranged (e.g. aligned with one another) such that the crane is operable to raise and lower the fuel handling grab through the elongate shield structure of the fuel assembly shield for drawing the fuel assembly into the fuel assembly shield and for lowering the fuel assembly out of the fuel assembly shield.

In a third aspect, there is provided a method of transferring a fuel assembly for a nuclear reactor from a first location to a second location in a nuclear facility using the fuel handling apparatus of the second aspect, the method comprising the steps of: locating the first end of the fuel assembly shield directly above the grab end of the fuel assembly at the first location, the closure being in the open configuration; lowering the fuel handling grab through the fuel assembly shield towards the grab end of the fuel assembly and gripping the grab end of the fuel assembly; raising the fuel handling grab through the fuel assembly shield, thereby drawing the fuel assembly into the elongate shield structure; moving the closure to the closed configuration; transporting the fuel handling grab, fuel assembly and fuel assembly shield together from the first location to the second location; moving the closure to the open configuration; lowering the fuel handling grab through the fuel assembly shield, thereby lowering the fuel assembly out of the elongate shield structure; and releasing the grab end of the fuel assembly and raising the fuel handling grab through the fuel assembly shield away from the fuel assembly.

It will be appreciated that the various steps of the method may be carried out in any order. For example, it may be that the method comprises lowering the fuel handling grab through the fuel assembly shield before locating the end of the fuel assembly shield directly above the grab end of the fuel assembly at the first location.

Accordingly, in some examples, the method comprises: first, locating the first end of the fuel assembly shield directly above the grab end of the fuel assembly at the first location, the closure being in the open configuration; second, lowering the fuel handling grab through the fuel assembly shield towards the grab end of the fuel assembly and gripping the grab end of the fuel assembly; third, raising the fuel handling grab through the fuel assembly shield, thereby drawing the fuel assembly into the elongate shield structure; fourth, moving the closure to the closed configuration; fifth, transporting the fuel handling grab, fuel assembly and fuel assembly shield together from the first location to the second location; sixth, moving the closure to the open configuration; seventh, lowering the fuel handling grab through the fuel assembly shield, thereby lowering the fuel assembly out of the elongate shield structure; and, eighth, releasing the grab end of the fuel assembly and raising the fuel handling grab through the fuel assembly shield away from the fuel assembly. Alternatively, the method may comprise: first, lowering the fuel handling grab through the fuel assembly shield; second, locating the first end of the fuel assembly shield directly above the grab end of the fuel assembly at the first location; third, gripping the grab end of the fuel assembly; fourth, raising the fuel handling grab through the fuel assembly shield, thereby drawing the fuel assembly into the elongate shield structure; fifth, moving the closure to the closed configuration; sixth, transporting the fuel handling grab, fuel assembly and fuel assembly shield together from the first location to the second location; seventh, moving the closure to the open configuration; eighth, lowering the fuel handling grab through the fuel assembly shield, thereby lowering the fuel assembly out of the elongate shield structure; and, ninth, releasing the grab end of the fuel assembly and raising the fuel handling grab through the fuel assembly shield away from the fuel assembly.

It may be that the nuclear facility is a nuclear power plant comprising a nuclear reactor. It may be that one of the first and second locations is a nuclear reactor core and the other of the first and second locations is a fuel assembly storage area (i.e. a spent fuel area), such as a fuel assembly storage rack (e.g. in a spent fuel pool). Alternatively, it may be that the nuclear facility is a nuclear fuel reprocessing facility (i.e. a reprocessing plant) or a nuclear fuel storage facility (e.g. a wet storage facility).

In each of the first, second or third aspects, the nuclear reactor may be a light water reactor (LWR) such as a pressurised water reactor (PWR), for example a small modular reactor (SMR). Alternatively, it may be the nuclear reactor is a boiling water reactor (BWR) or a supercritical water reactor (SCWR).

The skilled person will appreciate that, except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore, except where mutually exclusive, any feature described herein may be applied to any aspect and/or combined with any other feature described herein.

Brief description of the Drawings

Embodiments will now be described by way of example only, with reference to the Figures, in which: Figure 1 is a perspective view of a fuel assembly shield; Figure 2 is a front view of a portion of the fuel assembly shield of Figure 2 in which a closure is arranged in a closed configuration; Figure 3 is a front view of the portion of the fuel assembly shield of Figure 2 and Figure 3 in which the closure is arranged in the open configuration; Figure 4 is a schematic illustration of a fuel assembly enclosed within a fuel assembly shield and suspended from a crane above a nuclear reactor core in a pressurised water reactor; and Figure 5 is a schematic illustration of a fuel assembly partially drawn into a fuel assembly shield having its closure in the open configuration.

Detailed description

Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.

With reference to Figure 1, a fuel assembly shield 1 comprises a shield structure 2 which is elongate and generally cuboidal in shape. In particular, the shield structure 2 extends along a longitudinal axis 3 between a first end 4A and a second end 4B. The shield structure 2 is formed from metal sheet walls enclosing a hollow interior space 5.

A plurality of apertures 6 are provided in each of the metal sheet walls such that the hollow interior space 5 is in communication with the exterior of the shield structure by way of the apertures 6.

The fuel assembly shield 1 has a closure 7 at the first end 4A. Figures 2 and 3 show in more detail the region A of Figure 1 including the closure 7. The closure 7 includes two hinged closure walls 8A and 8B. The closure walls 8A and 8B are hingedly attached to the shield structure 2 by way of respective hinges 9A and 9B, about which the closure walls 8A and 8B are pivotable between a closed configuration (as shown in Figure 2) and an open configuration (as shown in Figure 3). When in the closed configuration (Figure 2), the closure walls 8A and 8B extend across the open end 4A of the shield structure 2, thereby impeding insertion or removal of objects into or out of the shield structure though the end 4A. When in the open configuration (Figure 3), the closure walls 8A and 8B are retracted away from the open end 4A of the shield structure 2 such that insertion or removal of objects into or out of the shield structure 2 is not impeded by the closure 7. An actuator 8C is operatively coupled to the closure walls 8A and 8B and is operable to pivot the walls 8A and 8B about the hinges 9A and 9B.

In this example, the metal sheet walls of the shield structure 2 and the closure walls 8A and 8B are made of a boronated (i.e. borated) stainless steel alloy, for example conforming to ASTM standard A887. The boronated stainless steel contains boron which is a neutron absorber. However, the shield structure 2 and closure walls 8A and 8B may be made of any suitable material known in the art which is capable of withstanding the conditions found in a nuclear reactor (for example, which is capable of withstanding irradiation and/or corrosive environments) and which is sufficiently strong that the fuel assembly shield 1 could support the weight of a fuel assembly, which is typically about 350 kg. The material may incorporate one or more neutron absorbers, of which boron, xenon, cadmium, hafnium, gadolinium, cobalt, samarium, titanium, dysprosium, erbium, europium, molybdenum and ytterbium are examples.

The fuel assembly shield 1 is suitable for use in protecting a fuel assembly during transportation between locations within a nuclear facility, for example when transporting a spent nuclear fuel assembly from a reactor core to a spent fuel storage area such as a storage rack within a nuclear power plant. In this regard, Figure 4 illustrates schematically a fuel assembly 10 being transported away from a reactor core using fuel handling apparatus which includes a gantry crane 12 from which the fuel assembly 10 is suspended by way of a fuel handling grab 13 and a first telescopic handling mast 14. The fuel assembly 10 is enclosed within fuel assembly shield 1 which is independently suspended from the gantry crane 12 by a second telescopic handling mast 15. The closure 7 of the fuel assembly shield 1 is in the closed configuration in Figure 4.

The fuel handling apparatus 11 also includes a controller 16 operatively connected to the telescopic masts 14 and 15 and the closure actuator 8C. The controller 16 is programmed to control raising and lowering of the fuel handling grab 13 and the fuel assembly shield 1 by way of the telescopic masts 14 and 15. The controller 16 is also programmed to control opening and closing of the closure 7 by way of the closure actuator. For example, the controller 16 may be in electronic communication with a memory storing computer executable program code containing instructions for controlling raising and lowering of the telescopic masts 14 and 15 and opening and closing of the closure 7. In particular, the controller is able to raise and lower the fuel handling grab 13 and the fuel assembly shield 1 independently of one another. Accordingly, it is possible to move the fuel handling grab 13 and the fuel assembly shield 1 together (for example, during transportation of the fuel assembly 10 from the reactor core 11 to a storage area), and it is also possible to (a) move one of the fuel handling grab 13 and the fuel assembly shield 1 while holding the other component stationary or (b) move the fuel handling grab 13 and the fuel assembly shield 1 in opposite directions, so that it is possible to move the fuel handling grab 13 and the fuel assembly shield 1 relative to one another.

Movement of the fuel handling grab 13 and the fuel assembly shield 1 relative to one another is illustrated in more detail in Figure 5. In particular, Figure 5 shows a fuel assembly 10 which has been partially drawn into the shield structure 2 of the fuel assembly shield 1 with the closure 7 in the open configuration. Movement of the fuel assembly 10 into and out of the shield structure 2 is possible by aligning the fuel handling grab 13 with the longitudinal axis of the shield structure 2 and then moving the fuel handling grab 13 along the axis, as indicated by arrow B, by way of telescopic mast 14 while the fuel assembly shield 1 is held static (i.e. while telescopic mast 15 does not move). It is therefore possible to draw the fuel assembly 10 into the fuel assembly shield 1, or to lower the fuel assembly 10 out of the fuel assembly shield 1, by raising or lowering the fuel assembly grab 13 through the shield structure 2 respectively.

A fuel assembly 10 may therefore be transferred from the reactor core 11 to a storage area (not shown) by the following method. The first end 4A of the fuel assembly shield 1 is located directly above a grab end of the fuel assembly 10 in the reactor core 11 by moving the telescopic masts 14 and 15 by way of the crane 12. The closure 7 is either already in the open configuration or is moved to the open configuration by the actuator. The fuel handling grab 13 is lowered through the fuel assembly shield 1 towards the grab end of the fuel assembly 10 by the telescopic mast 15 and then the fuel handling grab 13 grips the grab end of the fuel assembly 10. Once the fuel assembly 10 is gripped, the fuel handling grab 13 is raised by the telescopic mast 15 through the fuel assembly shield 1, thereby drawing the fuel assembly 10 out of the reactor core 11 and into the shield structure 2. Once the fuel assembly 10 is entirely housed within the shield structure 2, the closure is moved to the closed configuration by the actuator 8C. The fuel handling grab 13, fuel assembly 10 and fuel assembly shield 1 are then moved together from the reactor core 11 to the storage area. The process is then reversed in order to open the closure 7 and to lower the fuel assembly 10 out of the fuel assembly shield 1 into the storage area.

Because the fuel assembly 10 is housed within the fuel assembly shield 1 during transportation between the reactor core 11 and the storage area, the likelihood of a criticality accident is reduced, even if the fuel handling grab 13 loses power or malfunctions. In particular, because the closure 7 is held in the closed configuration during transportation of the fuel assembly 10, the fuel assembly 10 is retained within the fuel assembly shield 1 even if the fuel handling grab 13 ceases to grip the fuel assembly. The fuel assembly 10 is therefore prevented from falling into the reactor by the fuel assembly shield 1. Moreover, if the fuel handling grab 13 loses grip of the fuel assembly, any distance through which the fuel assembly 10 falls within the fuel assembly shield 1 is relatively short such that impact forces on the fuel assembly are minimal and the likelihood of an impact leading to a criticality event is reduced.

Transportation of the fuel assembly 10 typically takes place underwater in light water reactors such as pressurised water reactors. Because the shield structure 2 comprises a plurality of apertures 6, the fuel assembly 10 continues to be bathed in water within the fuel assembly shield 1 as the fuel assembly 10 is transported between locations. Indeed, water is able to circulate around the fuel assembly 10 within the fuel assembly shield 1 as the fuel assembly 10 is transported between locations. Circulation of water around the fuel assembly 10 cools the fuel assembly, further reducing the likelihood of a criticality event occurring if the fuel handling grab fails.

In addition, because the fuel assembly shield 1 is made of a neutron-absorbing material such as boronated stainless steel, neutrons emitted by the fuel assembly 10 during transportation are absorbed by the fuel assembly shield 1, again further reducing the likelihood of a criticality accident occurring in the event of a fuel handling grab failure. Indeed, by lowering the fuel assembly shield 1 to directly above the reactor core prior to drawing the fuel assembly 10 into the shield 1, and by lowering the fuel assembly shield 1 to the storage area before lowering the fuel assembly 10 out of the shield 1, the fuel assembly remains shielded by neutron-absorbing material as it is drawn out of the reactor core or is lowered into a storage rack, and the escape of neutrons emitted by the fuel assembly 10 into the surroundings is significantly reduced.

Accordingly, use of the fuel assembly shield 1 during transportation of a fuel assembly enables substantial control of criticality through multiple mechanisms. At present, criticality control in pressurised water reactors during fuel assembly handling is achieved in part through use of soluble boron (i.e. boric acid or boric acid salts) dissolved in the water which surrounds the reactor core, the soluble boron acting as a neutron-absorber for absorbing neutrons emitted by the fuel assembly being moved.

However, exposure to soluble boron in large quantities or over long timescales can be toxic and disposal of water contaminated with soluble boron may be difficult or restricted due to environmental concerns. The use of soluble boron in nuclear reactors may be restricted or banned in some jurisdictions in the near future. Use of the fuel assembly shield of the present invention, however, permits safe transportation of fuel assemblies, while maintaining multiple modes of criticality prevention, without the use of soluble boron.

It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein.

In particular, it will be appreciated that the shape and dimensions of the elongate shield structure can be adapted for use with particular fuel assemblies as required. For example, the elongate structure could be hexagonal or circular in cross-section perpendicular to the longitudinal axis. Similarly, the shape, size, number and placement of the apertures in the elongate shield structure could be varied. The fuel handling grab and the fuel assembly shield could be suspended from any type of platform or crane, including a tower crane, gantry crane or overhead crane, and suspension could be achieved using any suitable type of mast or hoist arrangement.

The fuel assembly shield closure could be replaced by any actuatable type of closure known to the person skilled in the art, so long as the closure can be moved between an open configuration, in which a fuel assembly can be inserted into or removed from the fuel assembly shield, and a closed configuration, in which a fuel assembly can be retained within the fuel assembly shield, even when the fuel handling grab fails to grip the fuel assembly. For example, the two closure walls 8A and 8B could be replaced by a single closure wall which extends across part or all of the first end 4A when in the closed configuration. The or each closure wall could be pivotably, hingedly or slidably attached to the elongate shield structure and the actuator could be selected from any type known in the art which is suitable for actuating movement of the chosen closure between the open and closed configurations.

The method may be used to transport fuel assemblies between locations within different types of nuclear facility other than a nuclear power plant, for example within a fuel reprocessing facility or within a fuel storage facility.

Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

Claims

CLAIMS1. A fuel assembly shield (1) for protecting a fuel assembly (10) during refuelling of a nuclear reactor, the fuel assembly shield (1) comprising: an elongate shield structure (2) for surrounding the fuel assembly (10); and a closure (7) movable between an open configuration in which an end (4A) of the elongate shield structure (2) is open for insertion or removal of the fuel assembly (10) and a closed configuration in which the end (4A) of the elongate shield structure (2) is closed for retention of the fuel assembly (10) within the elongate shield structure (2).
The fuel assembly shield (1) according to claim 1, wherein the elongate shield structure (2) has first and second ends (4A, 4B), the closure (7) being provided at the first end (4A) and the elongate shield structure (2) having an opening at the second end (4B) for insertion or removal of a fuel handling grab (13).
The fuel assembly shield (1) according to claim 1 or claim 2, wherein the elongate shield structure (2) comprises a plurality of apertures (6) to enable circulation of fluid around the fuel assembly (10) when enclosed therein.
The fuel assembly shield (1) according to claim 3, wherein the elongate shield structure (2) is a cage.
The fuel assembly shield (1) according to any preceding claim, wherein the closure (7) is a hinged closure (7).
The fuel assembly shield (1) according to any preceding claim, wherein the elongate shield structure (2) and/or the closure (7) comprise a material containing a neutron absorber, for example an isotope having a thermal neutron capture cross section greater than about 100 barn and a negligible thermal neutron fission cross section.
The fuel assembly shield (1) according to claim 6, wherein the neutron absorber is selected from isotopes of: boron (B), xenon (Xe), cadmium (Cd), hafnium (Hf), gadolinium (Gd), cobalt (Co), samarium (Sm), titanium (Ti), dysprosium (Dy), erbium (Er), europium (Eu), molybdenum (Mo), and ytterbium (Yb). 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.
The fuel assembly shield (1) according to claim 6 or claim 7, wherein the material is a metal alloy, for example a stainless steel.
A fuel handling apparatus for use in refuelling a nuclear reactor, the fuel handling apparatus comprising: a fuel handling grab (13) for gripping a grab end of a fuel assembly (10); a fuel assembly shield (1) according to any one of claims 1 to 8; and an actuator (8C) for moving the closure between the open and closed configurations.
The fuel handing apparatus according to claim 9, wherein the fuel handling grab (13) and the fuel assembly shield (1) are both suspended from a crane (12), the crane (12) being operable to lower and raise the fuel handling grab (13) and the fuel assembly shield (1).
The fuel handling apparatus according to claim 10 or claim 11, wherein the fuel handling grab (13) and the fuel assembly shield (1) are suspended from the crane (12) such that the fuel handling grab (13) and the fuel assembly shield (1) are independently movable.
The fuel handling apparatus according to claim 11, further comprising a controller (16) configured to cause relative movement between the fuel handling grab (13) and the fuel assembly shield (1).
The fuel handling apparatus according to any one of claims 9 to 12, wherein each of the fuel handling grab (13) and the fuel assembly shield (1) is independently suspended from the crane (12) by a telescopic handling mast (14, 15).
The fuel handling apparatus according to any one of claims 10 to 13, wherein the fuel handling grab (13) and the fuel assembly shield (1) are arranged such that the crane (12) is operable to lower and raise the fuel handling grab (13) through the elongate shield structure (2) of the fuel assembly shield (1).
A method of transferring a fuel assembly (10) for a nuclear reactor from a first location to a second location in a nuclear facility using the fuel handling apparatus of any of claims 9 to 14, the method comprising the steps of: locating the first end (4A) of the fuel assembly shield (1) directly above the grab end of the fuel assembly (10) at the first location, the closure (7) being in the open configuration; lowering the fuel handling grab (13) through the fuel assembly shield (1) towards the grab end of the fuel assembly (10) and gripping the grab end of the fuel assembly (10); raising the fuel handling grab (13) through the fuel assembly shield (1), thereby drawing the fuel assembly (10) into the elongate shield structure (2); moving the closure (7) to the closed configuration; transporting the fuel handling grab (13), fuel assembly (10) and fuel assembly shield (1) together from the first location to the second location; moving the closure (7) to the open configuration; lowering the fuel handling grab (13) through the fuel assembly shield (1), thereby lowering the fuel assembly (10) out of the elongate shield structure (2); and releasing the grab end of the fuel assembly (10) and raising the fuel handling grab (13) through the fuel assembly shield (1) away from the fuel assembly (10).
16. The method according to claim 15, wherein one of the first and second locations is a nuclear reactor core and the other of the first and second locations is a fuel assembly storage rack.
17. The fuel assembly shield (1), fuel handling apparatus or method according to any preceding claim, wherein the nuclear reactor is a pressurised water reactor (PWR), for example a small modular reactor (SMR).