Radiation shield and a method of manufacturing the same

Abstract

The present invention relates to a radiation shield comprising at least a first plate and a second plate, wherein the first and second plates are stacked, wherein the stacked first and second plates are bonded to one another, and wherein an edge of the first plate is staggered with respect to an edge of the second plate for interlocking with edges of a corresponding at least first and second plate of an adjacent radiation shield.

Description

Radiation Shield and a Method of Manufacturing the sameField of disclosure

[0001] The present invention relates to a radiation shield, a method of manufacturing the same, and a radiation assembly comprising a plurality of radiation shields.Background

[0002] As the demand for greener, cleaner energy grows, the energy sector shows an increasing interest in nuclear fusion energy technology. Nuclear fusion is a physical reaction where two nuclei fuse together, in response to them overcoming their Coulombic repulsion. Nuclear fusion energy technology exploits this fundamental nuclear reaction, for example, through the fusion of two isotopes of hydrogen.

[0003] Nuclear fusion reactors require extremely high energy levels in order to force isotopes of, e.g., hydrogen close enough together to cause a fusion reaction. Fusion reactions release an extremely large amount of heat energy and neutrons. Neutron radiation can damage sensitive components of the nuclear reactor and can be damaging to the wider environment.

[0004] A problem with conventional radiation shields for neutron shielding is the presence of continuous gaps or spacing leading from the interior of the reactor, through the radiation shield and to the exterior of the reactor, known as shine paths. Shine paths enable radiation leakage, which can be damaging to sensitive and fragile components of the nuclear reactor and human health.

[0005] Neutron microscopic cross section is an intrinsic property of every isotope, and macroscopic cross section is the microscopic cross section multiplied by the density of the material. To develop dense, compact, radiation shielding for neutron shielding, a high neutron macroscopic cross sections are required for high performance. In addition, shielding against gamma-ray and x-rays is required, and the cross section of capture generally increases with the Z element number.

[0006] In a fusion-neutron environment, geometric constraints, neutron shielding performance, and element activation limit material choices for shielding (of suchcomponents as magnets, diagnostics, vacuum vessels, and cabling). One such example material is tungsten (W), which has a high thermal conductivity, large neutron cross-section of absorption, high melting point, and good mechanical properties at elevated temperatures. However, tungsten has poor joinability and formability, limiting the geometries (shape and size) which can be achieved and thus restricting its application. This is similarly realised in ceramic materials such as carbides and borides which have good radiation properties, but severe limitations in formability and maximum component geometries.

[0007] Hafnium is another material which may be used for radiation shielding. Hafnium is a severely reactive refractory metal which severely limits processing routes and methods of joining hafnium components. Accordingly, it is not possible to manufacture large billet material comprising hafnium. It is also very challenging to cast hafnium. Instead, hafnium is typically processed from powder. This results in sintering products of limited thickness and joining processes requiring aid. Hafnium carbide is another candidate material for radiation shielding. Hafnium carbide has an extremely high melting point (3,958 °C) meaning that it is exceptionally difficult to handle and process.

[0008] Conventionally, it is difficult to produce a thick-sectioned material with high neutron capture capability. For protecting fragile / sensitive materials from fusion neutron radiation, material thicknesses may need to be in the range of e.g. 80-200 mm. Such thicknesses cannot easily be achieved with conventional processing techniques such as powder sintering.

[0009] US2023025227A1 relates to a neutron shield that is a “sandwich” of tungsten boride and metal hydride, with two layers of tungsten boride and a layer of metal hydride therebetween.

[0010] Interlocking lead chevron bricks for radiation shielding and elimination of shine paths have been proposed. However, lead has a melting point of 327.5 °C. The thermal and neutronic power on the walls, and solid bodies of a plasma fusion reactor will provide temperatures that exceed this value, meaning that lead does not have the structural integrity to maintain its shape in situ.Summary of Invention

[0011] According to a first aspect of the invention there is provided a radiation shield comprising at least a first plate and a second plate, wherein the first and second plates are stacked, wherein the stacked first and second plates are bonded to one another, and wherein an edge of the first plate is staggered with respect to an edge of the second plate for interlocking with edges of a corresponding at least first and second plate of an adjacent radiation shield.

[0012] Advantageously, the plates of the radiation shield are arranged such that an edge of a first plate is staggered with respect to an edge of a second plate. The staggered edges allows the radiation shield to be interlocked or connected with similar radiation shields having staggered edges. This enables formation of a radiation shield assembly which has good joinability and formability properties, thus increasing geometry flexibility of the radiation shield assembly. At the same time, when the staggered edges of adjacent radiation shields interlock, a staggered, stepped, or labyrinthine abutment is formed (i.e. the edges of adjacent radiation shields closely abut one another, but the join between the adjacent radiation shields is not planar across the abutted edge). This eliminates radiation shine paths that would otherwise be present if the radiation shields had flat edges and hence planar abutments. Additionally, the staggered edges minimise the amount of subtractive machining processes required to allow a joint to be formed between radiation shields.

[0013] Preferably, the at least first plate and second plate comprise a plurality of sheets, wherein a bonding material is present between the sheets. Preferably, the radiation shield comprises two to fifty plates.

[0014] In some embodiments, a bonding material is present between the at least first plate and the second plate. Preferably, the bonding material is one of an interlayer, a glue, a powder, or a powder-binder paste. Preferably, the bonding material comprises copper, titanium, vanadium or tantalum.

[0015] Preferably, the at least first and second plates comprise tungsten, yttrium, hafnium, zirconium, lithium, dysprosium, or steel. More preferably, the at least first and second plates comprise tungsten boride, tungsten carbide, zirconium hydride,hafnium hydride, hafnium diboride, yttrium hydride, boron carbide, lithium hydride, dysprosium titanate or boronated steel.

[0016] In some embodiments, the at least first and second plates are curved.

[0017] The radiation shield preferably further comprises a third plate, wherein the second plate is positioned between the first plate and the third plate, and the second plate comprises an internal channel for coolant. More preferably, the internal channel for coolant is serpentine.

[0018] According to a second aspect of the invention there is provided a radiation shield assembly comprising at least two radiation shields according to the first aspect of the invention, wherein the at least two radiation shields are joined together along their reciprocating staggered edges.

[0019] According to a third aspect of the invention, there is provided a method of manufacturing a radiation shield comprising the steps of providing a first plate; providing a second plate on the first plate; wherein an edge of the first plate is staggered with respect to an edge of the second plate; and bonding the first plate to the second plate to create a radiation shield.

[0020] The method of manufacturing a radiation shield overcomes the problem associated with conventional processing of materials for neutron and electromagnetic radiation (such as gamma rays, x-rays, protons, alpha and beta) shielding, in that a radiation shield having a thickness suitable for radiation shielding can be efficiently processed to a near net shape, thus increasing the flexibility of application of the radiation shield.

[0021] Preferably, wherein the at least first and second plates comprise tungsten, yttrium, hafnium, zirconium, lithium, dysprosium, or steel. More preferably, the at least first and second plates comprise tungsten boride, tungsten carbide, zirconium hydride, hafnium hydride, hafnium diboride, yttrium hydride, boron carbide, lithium hydride, dysprosium titanate or boronated steel.

[0022] Preferably, a third plate is bonded to the second plate, such that the second plate is positioned in between the first plate and the third plate, and wherein an edge of the third plate is staggered with respect to an edge of the second plate.

[0023] In some embodiments, bonding the first plate to the second plate comprises applying a bonding material between the first plate and the second plate. Preferably, the bonding material is one of an interlayer, a glue, a powder, or a powder-binder paste. More preferably, the bonding material comprises copper, titanium, vanadium, iron, or tantalum.

[0024] Preferably, bonding the first and second plates together comprises physical or chemical vapour deposition, brazing or diffusion bonding.

[0025] Preferably, bonding the first plate to the second plate does not require application of a bonding material between the first plate and the second plate. More preferably, a method of bonding the first and second plates together comprises welding, for example, explosion welding, magnetic pulse welding or cold welding.

[0026] According to a fourth aspect of the invention, use of a radiation shield according to the first aspect, or a radiation shield assembly according to the second aspect in a nuclear fusion reactor is provided.

[0027] According to a fifth aspect of the invention, there is provided a radiation shield comprising at least a first plate and a second plate, wherein the first and second plates are stacked, wherein the stacked plates are bonded to one another, wherein the at least first and second plates are curved and wherein the at least first and second plates comprise tungsten.

[0028] According to a sixth aspect of the invention, there is provided an apparatus for aligning at least first and second plates of a radiation shield prior to bonding, wherein the apparatus is configured to stagger an edge of the first plate with respect to an edge of the second plate.

[0029] In order that the present invention be more readily understood, various aspects of specific embodiments will now be described in conjunction with the attached drawings.Brief description of the drawings

[0030] The drawings are included for illustrative purposes only.

[0031] Fig. l is a perspective view of a radiation shield comprising seven plates.

[0032] Fig. 2a is a perspective view of a radiation shield comprising four plates, showing the staggered edges of the plates. Fig. 2b is a top-down perspective view of the radiation shield of Fig. 2a.

[0033] Fig. 3 is a perspective view of a radiation shield assembly including four of the radiation shields as shown in Fig. 1.

[0034] Fig. 4 is a close-up view of the joint between two radiation shields in the radiation shield assembly of Fig. 3.

[0035] Fig. 5a is an exploded perspective view of an apparatus for holding a stack of plates while they undergo a bonding process. Fig. 5b is a perspective view of the apparatus of Fig. 5a.

[0036] Fig. 6a is an exploded view of a radiation shield having a channel for coolant therein. Fig. 6b is a perspective view of the radiation shield of Fig. 6a.

[0037] Fig. 7 is an exploded view of a radiation shield with a channel insert for forming the channel for coolant in one of the plates.

[0038] Fig. 8 is a flow chart showing an exemplary method of manufacture, starting with sheets and culminating in a radiation shield assembly.Detailed description

[0039] The present invention generally relates to radiation shielding. The radiation to be shielded may include neutrons, gammas, x-rays, protons, beta, and alpha radiation, but is not limited thereto. More particularly, the present invention relates to a radiation shield comprising stacked, bonded plates, wherein the plates are arranged such that an edge of a first plate is staggered with respect to an edge of a second plate. The staggered edges allows the radiation shield to be interlocked or connected with similar radiation shields having staggered edges. This enables formation of a radiation shield assembly which has good joinability and formability properties,thus increasing geometry flexibility of the radiation shield assembly. In this regard, the staggered edges minimise the amount of subtractive machining processes required to allow a joint to be formed between radiation shields.

[0040] When the staggered edges of adjacent radiation shields interlock, a staggered, stepped, or labyrinthine abutment is formed (i.e. the edges of adjacent radiation shields closely abut one another, but the join between the adjacent radiation shields is not planar across the abutted edge). This eliminates radiation shine paths that would otherwise be present if the radiation shields had flat edges and hence planar abutments.

[0041] In particular, when two radiation shields having flat, planar edges are placed together in a radiation shield assembly, a shine path exists between the two radiation shields as the abutted planar edges allow radiation to travel in an essentially straight line between the adjacent radiation shields with minimal interaction with the material of the radiation shield itself. With the present invention, shine path formation is minimised between adjacent abutted / connected radiation shields.

[0042] Fig. 1 shows a radiation shield 10 comprising a bonded stack of plates. In the example shown, there are seven plates, 12-18. There may be more or fewer than seven plates in a radiation shield 10, depending on the thickness of radiation shield required. E.g. there may be from three to nine plates (but at least two plates are present). Preferably an odd number of plates make up a shield.

[0043] Each plate 12-18 in Fig. l is made up of four generally square equal-sized sheets or plies, bonded together to form a single laminated plate. The sheets of a plate are aligned together at their edges. There may be more or fewer than four sheets in a plate. Thus, each plate may have a ply form, but this is not essential and indeed, each sheet can be monolithic / unitary as will be described below.

[0044] The sheets (plies) and therefore the plates 12-18 may be ceramic or metallic. In particular, the sheets and thus plates 12-18 may be made of tungsten, yttrium, hafnium, zirconium, lithium dysprosium or steel. In particular, the sheets and plates 12-18 may be made of tungsten boride, tungsten carbide, zirconium hydride, hafnium hydride, hafnium diboride, yttrium hydride, boron carbide, lithiumhydride, dysprosium titanate or boronated steel.. The sheets and plates 12-18 may be made of alloys of any of the materials listed above.

[0045] Each of the sheets (plies) has a thickness of 0.5-8 mm. Plates 12-14 and 16-18 are of substantially equal thickness (i.e. 2-32 mm), whereas central plate 15 is shown as being thinner than the plates 12-14 and 16-18. E.g. central plate 15 may comprise just one, two or three plies. In alternative arrangements, the plates may all be of equal thicknesses, or each have different thicknesses.

[0046] The radiation shield is approximately 600 mm (h) x 600 mm (w) x 150 mm (d) and weighs approximately 150-800kg depending on the material, but this is merely an example, and it is preferably generally a rectangular shape with a width-to-thickness ratio of between about 1 : 1 and 8: 1. However, the skilled person would understand that the width-to-thickness ratio could be lower than about 1 : 1, depending on the availability of ready forms of the sheets and / or depending on the composition of the material.

[0047] The sheets and thus plates 12-18 are curved about the y-axis. Curvature may also be present in x- and / or z-axes. Curvature of plates 12-18 allows the radiation shield 10 to be used in nuclear fusion devices, e.g. a tokamak (a device for confining a plasma using magnetic fields having a toroidal shape). In an alternative embodiment, the sheets and plates 12-18 may be planar (flat). In use, the radiation shield 10 is positioned to protect sensitive components from radiation damage by capturing neutrons, gamma-rays, protons, x-rays, beta and / or alpha. The radiation shield 10 may be used alone, or as shown in Fig. 3, the radiation shield 10 may form part of a radiation shield assembly 30 including a plurality of connected radiation shields.

[0048] In the orientation of Fig. 1, the top edges of plates 12-14 are off-set relative to each other such that they form steps up to central plate 15. The top edges of plates 16-18 are stepped down from central plate 15 (i.e. on the other / opposite side of plate 15) by the same offset. Thus, the edges of adjacent plates of the radiation shield 10 are off-set from each other, forming a staggered arrangement.

[0049] The edges of plate 12 are referred to as 12a-12d. As shown in Fig. 1, edges 12a-12d are off-set from the corresponding edges of adjacent plate 13. In effect, edges 12a-12d of plate 12 are not aligned with the corresponding edges of plate 13. The edges of plate 13 are also off-set from the edges of adjacent plate 14. The edges of plates 16-18 are also off-set from the edges of the plate adjacent thereto.

[0050] The degree of off-set is about 2% of the plate width, and each step has the same offset, but the degree of offset can be greater or less (e.g. 1% to 15%), and the steps need not be equal. There may be symmetry in the steps about the central plate. I.e. steps on either side of the central plate have equal and opposite offsets and it is preferred that the outermost pairs of plates on each side have equal and opposite offsets.

[0051] A purpose of the staggered edges is to allow the radiation shield 10 to tesselate with and join snugly (i.e. interlock) to at least a second radiation shield 10 along an at least one staggered edge of that second radiation shield 10. Thus, easy connection between similar radiation shields is realised, allowing for a higher degree of flexibility in the size and shape of radiation shield assemblies, thus increasing the number of applications in which they can be applied.

[0052] A further purpose of the staggered edges is to minimise the amount of subtractive machining processes required to allow a joint to be formed between radiation shields. The plate-plate joint preferably has a tolerance requiring only surface dressing to allow the components to be joined to form a radiation shield.

[0053] Advantageously, the staggered edges create a discontinuous join between two radiation shields, which minimises formation of shine paths and therefore optimises protection of sensitive / fragile components against harmful radiation. It is not necessary that the edges of each of the plates of the radiation shield are staggered or misaligned with respect to the edge of every other plate. For example, the edges of plate groups 1) plates 12 and 18, 2) plates 13 and 17, and 3) plates 14 and 16 are not staggered with respect to one another. It is staggering of edges between adjacent plates which facilitates interlocking between a radiation shield and a corresponding other radiation shield. Due to the stepped / staggered edges of the radiation shield 10, a discontinuous join between two radiation shields is formed, which is shown in Figs. 3 and 4 and discussed below.

[0054] Various methods can be used to bond the sheets together to form each plate 12-19. Such methods can also be used to bond plates 12-19 together to form the radiation shield 10. These bonding methods fall into two categories: 1) those which do not use a bonding material (also referred to as bonding aid) in between the sheets or plates; and 2) those which use a bonding material between the sheets or plates.

[0055] Category 1 includes methods such as welding, e.g. explosion / magnetic pulse welding or cold welding. Prior to cold welding, the oxide layer on the sheets or plates can be removed (i.e. the sheets or plates are cleaned prior to cold welding).

[0056] Other methods which do not use a bonding material between the sheets or plates include sintering, e.g. nanoparticulate sintering and field assisted sintering. Nanoparticulate sintering involves applying a temperature (e.g., approximately 1,000 to 1,400 °C) and, often, a pressure (e.g., approximately 20 to 150 MPa) to the surface of the sheet or plate in order to drive diffusion of atoms between particles, and particle-plate (i.e. between particles of a first plate and particles of a second plate). Therefore, there is intra-plate and inter-plate bonding. There is a driving force to reduce the total free surface area, meaning that sub-micron particles require a lower activation energy to diffuse than larger particles. This results in stronger metal -metal (or ceramic-ceramic) joints. Nanoparticulate sintering requires lower temperatures and pressures compared with sintering of conventional powders (typically 20-40 pm d50), which requires temperatures in the range of 1,500 to 1,900 °C and pressures over 100 MPa.

[0057] Field assisted sintering involves applying high intensity, low voltage, pulsed current to sinter metal or ceramic materials together, whereby resistive heating occurs at interfaces leading to locally high temperatures and current assisted diffusion of atoms.

[0058] Category 2 includes deposition methods such as physical vapour deposition (PVD) or chemical vapour deposition (CVD). The bonding material to be deposited on the surface of the plate or sheet may be a foil, a powder or a powder-binder paste. Another method requiring a bonding material / aid is brazing, which involves introducing a filler metal (bonding material) between the plates and joining the plates by heating. The filler metal may comprise copper, titanium, vanadium, iron,or tantalum, which are particularly effective when bonding tungsten plates or sheets. The skilled person would understand that the choice of filler metal depends on the material of the plates. Diffusion bonding using an interlayer between the plates may also be used. Alternatively, the plates may be glued together.

[0059] Figs. 2a and 2b show radiation shield 20, which includes five stacked and bonded plates 21-25. Plates 21-25 are made from bonded sheets (comprising, e.g., tungsten). Like in the arrangement of Fig. 1, the plates 21-25 are rectangular and are curved in the x-y plane, so that the radiation shield 20 is suitable for use in a radiation-rich environment without substantial subtractive machining processes.

[0060] The staggered arrangement of the edges of the plates 21-25 can be clearly seen from different perspectives in Figs. 2a and 2b. Referring to Fig. 2a, the top edges of plates 21 and 22 are stepped up towards central plate 23, with the top edge of plate 21 being the lowest and the top edge of plate 23 being the highest. Plates 24 and 25 are stepped downwards from plate 23, in that order. In this example, the extent of plate- to-plate offset is about 10%.

[0061] The stepped arrangement forms a tongue-and-groove arrangement for connection to a similar radiation shield having a corresponding / reciprocal stepped arrangement, allowing formation of a radiation shield assembly. The stepped / staggered arrangement means that the joint between two (or more) radiation shields 20 is nonlinear. In effect, the joint is discontinuous. This arrangement minimises radiation emission through the joint between radiation shields and thus minimises shine paths. Accordingly, radiation leakage is minimised, prolonging the lifetime of component parts and removing local hot spots of the object being protected.

[0062] A radiation shield assembly 30 is shown in Fig, 3, which is formed of four connected radiation shields 31, 33, 35 and 37. Each radiation shield 31, 33, 35 is substantially the same as radiation shield 10 of Fig. 1. The radiation shield assembly 30 includes an upper layer 32 including radiation shields 31 and 33 arranged substantially horizontally (in the x-direction). The radiation shield assembly 30 further includes a lower layer 34 including radiation shields 35 and 37, which are also arranged substantially horizontally (in the x-direction).

[0063] Radiation shields 31 and 33 are positioned side-by-side and are joined along joint 36 via their staggered, interlocking / tessellating edges. Radiation shields 35 and 37 are also positioned side-by-side and are joined along joint 39. Part of the top staggered edge 352 of radiation shield 35 interlocks with part of the lower edge 311 of radiation shield 31. The other part of lower edge 311 of radiation shield 31 interlocks with part of the upper edge 372 of radiation shield 37. The other part of upper edge 372 of shield 37 interlocks with part of lower edge 331 of shield 33. The joints 39 and 36 are off-set in the x-direction, which strengthens the radiation assembly 30, i.e., by preventing lateral displacement. The portion of joint 36 extending from the front to the back of the radiation shield assembly 30 is labelled 38 and is shown in more detail in Fig. 4.

[0064] The connected staggered edges of adjacent and connecting radiation shields 31, 33, 35 and 37 effectively form a tongue-and-groove configuration (which can be seen in more detail in Fig. 4). In effect, protruding parts of the edge of one radiation shield are accommodated in corresponding depressions in an edge the adjacent radiation shield. This allows for formation of a strong mechanical connection between radiation shields, while minimising shine paths through the join between two connected radiation shields.

[0065] Fig. 4 shows a top view of the upper layer 32 of radiation shield assembly 30 including radiation shields 31 and 33 and the join 39 therebetween. Incoming radiation 42, which is shielded or blocked by the radiation shield assembly.

[0066] As shown in Fig. 4, joint 39 between radiation shields 31 and 33 is discontinuous in the z-direction and creates a tortuous route for passage of radiation, therefore minimising shine paths through the shield assembly. Consequently, radiation leakage is reduced, improving protection of sensitive / fragile components.

[0067] Radiation shield 31 includes plates 313-319 extending in the z-direction and radiation shield 33 includes plates 333-339 extending in the z-direction. The z- direction extends through the depth of radiation shields 31, 33. Plate 313 of radiation shield 31 is adjacent and joined to plate 333 of radiation shield 33 in the x-direction. Plate 314 is adjacent and joined to plate 334 in the x-direction. The join or abutment between plates 313 and 333 is off-set in the x-direction from the joinbetween plates 314 and 334. In the orientation of Fig. 4, the join between plates 314 and 334 is below (and off-set from) the join between plates 313 and 333. Plate 313 extends / protrudes further in the x-direction than plate 333. Similarly, plate 315 is adjacent plate 335 in the x-direction and the joint between those two plates is offset with respect to the joint between plates 313 and 333 and the joint between plates 314 and 334.

[0068] Similarly, in the x-direction: plate 315 is adjacent and joined to plate 335; plate 316 is adjacent and joined to plate 336; plate 317 is adjacent and joined to plate 337; plate 318 is adjacent and joined to plate 338; and plate 319 is adjacent and joined to plate 339.

[0069] In the direction of arrow A, the joins between plates 313 and 333, plates 314 and 334 and plates 315 and 335 are stepped up, towards the join between central plates316 and 336. Subsequently, and in the direction of arrow A, the joins between plates317 and 337, plates 318 and 338 and plates 319 and 339 are stepped down from the join between central plates 316 and 336.

[0070] The off-set joints create a labyrinth / chevron / stepped type of joint between connecting sides of the plates of the radiation shields 31 and 33. This arrangement allows for interlocking of the radiation shields 31 and 33 without continuous gaps or spaces introduced by attachment of one radiation shield 31 and 33 to another. A tight fit is ensured, which reduces leakage of radiation (shine paths) through the structure and therefore optimises protection of sensitive / fragile components against harmful radiation.

[0071] In order to align the plates prior to (and during) bonding them to form a radiation shield, an apparatus 50, as shown in Fig. 5 may be used. This ensures production of a high tolerance net-shape radiation shield. Apparatus 50 allows the geometry / shape of the staggered edges to be achieved by holding the plates in a specific positionrelative to one another, and maintained during the bonding process, to enable precise manufacturing.

[0072] The apparatus 50 has a front panel 52, a back panel 54, two side panels 56a, 56b, an upper panel 58 and a lower panel 51. The side panels 56a, 56b and the upper and lower panels 58, 51 are shaped internally to correspond with the shape of staggered edges of the stacked plates. There is an opening 58a in upper panel 58 for insertion of evacuation tube 53. Evacuation tube 53 enables exhaust of gas from inside of the apparatus 50. The apparatus 50 is made of steel or any other material which can withstand high temperature and high pressure.

[0073] In use, as shown in Fig. 5b, the apparatus 50 is a chamber which encloses the stack of plates (not visible). Apparatus 50 may be used to hold the plates in position while they undergo hot isostatic pressing (HIP) as a bonding process, as discussed above. During HIP, the plates are subject to elevated temperatures (approximately 800 to 1400 °C) and isostatic gas pressure (typically argon at approximately 5 to 150MPa). In other embodiments, apparatus 50 may be used to align sheets of, e.g. tungsten, which are used to form the plates.

[0074] Alternatively, the apparatus 50 enclosing the stacked plates (or sheets) may be subject to a vacuum and heated in order to bond the plates together.

[0075] Alternatively, the apparatus 50, enclosing the stacked plates (or sheets) may be subject to a uniaxial bonding process with pressure applied evenly to the front panel 52 and back panel 54 whilst subject to elevated temperatures.

[0076] Fig. 6a shows an exploded view of alternative radiation shield 60, including five plates 61-65 and a coolant channel 68 running through the centre of the shield in the y-direction. As shown in Fig. 6, radiation shield 60 has two stacked plates 61 and 62, wherein plate 61 is on the outside of the shield 60 and plate 62 is adjacent to plate 61. Adjacent to plate 62 is central plate 63, which comprises two reciprocating parts 631, and 632. Plate 64 is adjacent central plate 63 and plate 65 is adjacent plate 64 and is on the outside of shield 60.

[0077] The two reciprocating parts 631, 632 have a gap or space between them. The gap forms a serpentine channel 67 through the centre of the radiation shield 60 in the y-direction. Channel 67 is therefore internal to radiation shield 60. The channel 67 includes a fluid inlet 68 and fluid outlet 69 and is suitable for running coolant through the radiation shield 60. The radiation shield 60 can thus act as a heat sink.

[0078] In other embodiments, channel 67 may have a different geometry, for example, it may be linear and / or include curves or bends. Alternatively, or additionally, the radiation shield 60 may include a plurality or network of channels 67 formed by gaps between plates. In other embodiments, a plurality of plates may include gaps which form channels through the radiation shield 60.

[0079] Fig. 6b shows a perspective view of radiation shield 60 (i.e. when the plates 61-65 are bonded with their edges in a staggered arrangement), wherein the fluid inlet 68 of channel 67 can be seen.

[0080] Fig. 7 is an exploded view of radiation shield 60 (prior to bonding). Spacer 601 is positioned between the reciprocating parts 631, 632 of plate 63 in order to maintain a gap between parts 631, 632 for formation of the channel 67. Spacer 601 may be made of the same material as apparatus 50, e.g., steel or any other material which can withstand high temperature and high pressure. The spacer 601 therefore enables formation of channel 67. In the arrangement of Fig. 7, spacer 601 is a bent iron pipe and has a serpentine shape. However, the spacer 601 is not limited to being made of iron or having a serpentine shape. For example, the spacer 601 could be of any shape, e.g. linear. Spacer 601 could be removed by etching and may be made of any material which can be etched, e.g. metals such as aluminium and copper.

[0081] When spacer 601 is hollow, it could be incorporated into the radiation shield (e.g. as a pressure retaining structural material). In effect, the spacer 601 may not necessarily require removal from the radiation shield. In such arrangements, the spacer 601 may be made of steel, which is suitable for use as a coolant carrier.

[0082] In an alternative arrangement, spacer 601 is solid and should be removed from the radiation shield, e.g., by melting. When the spacer 601 is to be removed by melting, it is made of a material having a lower melting point than the material of the plates (e.g. iron). Alternatively, a solid spacer 601 may be slowly etched out of the radiation shield.

[0083] In order to form the radiation shield 60, the plates 61, 62, 63, 64, 65 may be enclosed within apparatus 50, with spacer 601 positioned between reciprocating parts 631 and 632 in the x-y plane. Once the plates have undergone bonding, the iron spacer 601 is removed, e.g. by etching.

[0084] Alternatively, the spacer 601 may form part of the structural arrangement of the shield and can itself form the channel. In this instance, the spacer 601 is hollow and there is no need to remove the spacer 601 from the bonded plate (i.e., the spacer 601 forms part of radiation shield assembly 60).

[0085] Fig. 8 is a flowchart showing an exemplary method of manufacture of a radiation shield assembly, starting with sheets and culminating in a radiation shield assembly. The individual steps of Fig. 8 are discussed in more detail above.

[0086] Step 1 : plates are produced by conventional manufacturing processes. The plates may comprise tungsten, hafnium, hafnium diboride, boronated steel, dysprosium titanate, tungsten carbide. Specifically, the sheets may comprise tungsten boride, hafnium hydride, zirconium hydride, lithium hydride or yttrium hydride.

[0087] Step 2: the plates are formed to give curvature for use in a nuclear fusion reactor, by a conventional process such as hot rolling, or hot forming. The curvature may be in a single axis, or it may be in two axes.

[0088] Step 3 : a bonding material is added to the plates, e.g., on the surface of the plates to be bonded. Exemplary bonding materials are an interlayer, a glue, a powder, or a powder-binder paste. A bonding material is optional and only relevant if the bonding process requires a bonding material. Processes such as welding do not require a bonding material.

[0089] Step 4: the plates are stacked in an apparatus which is configured to hold the plates such that their edges are staggered with respect to an adjacent plate.

[0090] Step 5: a bonding process is initiated to fix the plates in a staggered position and thus create a radiation shield.

[0091] Step 6: the apparatus is removed from the radiation shield.

[0092] Step 7 : multiple radiation shields are connected together along their staggered edges to form a radiation shield assembly. The joins between the radiation shields are discontinuous / stepped in order to reduce radiation leakage and shine paths.

[0093] The present invention is not to be limited by the above-described aspects and embodiments, and that many variations are within the scope of the appended claims. The various aspects and embodiments may be combined if necessary and appropriate. The drawings serve as exemplary illustrations of the invention only, to aid understanding of the invention.

Claims

CLAIMS1. A radiation shield comprising at least a first plate and a second plate, wherein the first and second plates are stacked, wherein the stacked first and second plates are bonded to one another, and wherein an edge of the first plate is staggered with respect to an edge of the second plate for interlocking with edges of a corresponding at least first and second plate of an adjacent radiation shield.

2. A radiation shield according to claim 1, wherein the at least first plate and second plate comprise a plurality of sheets, wherein a bonding material is present between the sheets.

3. A radiation shield according to claim 1 or 2, wherein the radiation shield comprises two to fifty plates.

4. A radiation shield according to any preceding claim, wherein a bonding material is present between the at least first plate and the second plate.

5. A radiation shield according to any of claims 2 to 4, wherein the bonding material is one of an interlayer, a glue, a powder, or a powder-binder paste.

6. A radiation shield according to any of claims 2 to 5, wherein the bonding material comprises copper, titanium, vanadium, iron, or tantalum.

7. A radiation shield according to any preceding claim, wherein the at least first and second plates comprise tungsten, yttrium, hafnium, zirconium, lithium, dysprosium, or steel.

8. A radiation shield according to any preceding claim, wherein the at least first and second plates comprise tungsten boride, tungsten carbide, zirconium hydride, hafnium hydride, hafnium diboride, yttrium hydride, boron carbide, lithium hydride, dysprosium titanate or boronated steel.

9. A radiation shield according to any preceding claim, wherein the at least first and second plates are curved.

10. A radiation shield according to any preceding claim, further comprising a third plate, wherein the second plate is positioned between the first plate and the third plate, and the second plate comprises an internal channel for coolant.

11. A radiation shield according to claim 10, wherein the internal channel for coolant is serpentine.

12. A radiation shield assembly comprising at least two radiation shields according to any preceding claim, wherein the at least two radiation shields are joined together along their reciprocating staggered edges.

13. A method of manufacturing a radiation shield comprising the steps of providing a first plate; providing a second plate on the first plate; wherein an edge of the first plate is staggered with respect to an edge of the second plate; and bonding the first plate to the second plate to create a radiation shield.

14. A method according to claim 13, wherein the at least first and second plates comprise tungsten, yttrium, hafnium, zirconium, lithium, dysprosium, or steel.

15. A method according to claim 13 or 14, wherein the at least first and second plates comprise tungsten boride, tungsten carbide, zirconium hydride, hafnium hydride, hafnium diboride, yttrium hydride, boron carbide, lithium hydride, dysprosium titanate or boronated steel.

16. A method according to any of claims 13 to 15, wherein a third plate is bonded to the second plate, such that the second plate is positioned in between the first plate and the third plate, and wherein an edge of the third plate is staggered with respect to an edge of the second plate.

17. A method according to any one of claims 13 to 16, wherein bonding the first plate to the second plate comprises applying a bonding material between the first plate and the second plate.

18. A method according to claim 17, wherein the bonding material is one of an interlayer, a glue, a powder, or a powder-binder paste.

19. A method according to claim 17 or 18, wherein the bonding material comprises copper, titanium, vanadium, iron, or tantalum.

20. A method according to any one of claims 13 to 19, wherein a method of bonding the first and second plates together comprises physical or chemical vapour deposition, brazing or diffusion bonding.

21. A method according to any one of claims 13 to 16, wherein bonding the first plate to the second plate does not require application of a bonding material between the first plate and the second plate.

22. A method according to claim 21, wherein bonding the first and second plates together comprises welding, for example, explosion welding, magnetic pulse welding or cold welding.

23. Use of a radiation shield according to any of claims 1 to 11 or a radiation shield assembly according to claim 12 in a nuclear fusion reactor.

24. A radiation shield comprising at least a first plate and a second plate, wherein the first and second plates are stacked, wherein the stacked plates are bonded to one another, wherein the at least first and second plates are curved and wherein the at least first and second plates comprise tungsten.

25. An apparatus for aligning at least first and second plates of a radiation shield prior to bonding, wherein the apparatus is configured to stagger an edge of the first plate with respect to an edge of the second plate.

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