Method of forming an encapsulated product

Abstract

There is provided a method of forming an encapsulated product (200), the method comprising: forming a mixture of core particles (202) and a non-oxide ceramic material (204), infiltrating the mixture with a fluid polymer, and heating the infiltrated mixture to form the encapsulated product. Also provided is an encapsulated product (200).

Description

Method of forming an encapsulated productField of the Invention

[0001] The present disclosure relates to a method of forming an encapsulated product and an encapsulated product. In particular, examples in the present disclosure relate to a method of forming a fuel product for use in a nuclear reactor and a fuel product.Background

[0002] High-temperature gas-cooled reactors are next-generation fission reactors that use tri-structural isotropic (TRISO) coated particle fuel. TRISO coated particle fuel comprises a fuel kernel, e.g. a fissile fuel kernel, which may comprise uranium, uranium oxycarbide, uranium dioxide, or uranium nitride, coated in a buffer layer and subsequent layers of pyrolytic carbon and silicon carbide. These fuel particles are typically approximately a millimetre in diameter, and millions of these particles will be required to run a fission reactor. Similar fission reactors may use bi-structural isotropic (BISO) coated particle fuel, or quadruple-structural isotropic (QUADRISO) coated particle fuel. Alternative reactors may use the same fuels, for example molten salt cooled high temperature reactors, or in light water reactors.

[0003] To enhance fuel handling, fuel processing and fuel safety, it is desirable to encapsulate fuel particles, for example TRISO coated particle fuels, in a fuel product, such as a fuel pellet or fuel pebble, that is a few centimetres in size, with a high density of fuel particles.

[0004] Fully ceramic micro-encapsulated (FCM) fuel products have been proposed in which the TRISO particles are encapsulated in a ceramic matrix such as silicon carbide. However, it has been challenging to develop a method of encapsulating the fuel particles that avoids damaging the fragile TRISO coated particle fuels, which can crack under high temperature or pressure, leading to the escape of gases. Existing methods of encapsulation include hot-pressing, spark-plasma sintering, binder jetting, and reactive melt infiltration.

[0005] Hot-pressing involves mixing the TRISO coated particle fuels with fine powders and sintering under high pressure and high temperatures. The uniaxial pressure applied during hot-pressing can cause the TRISO coated particle fuels to crack and fail. Sintering additives may be included to promote sintering at lower temperatures, however these additives do not perform well under exposure to corrosive substances, even water.

[0006] Spark-plasma sintering is a similar process to hot-pressing, but ratherthan using heating elements to heat a die containing the powders and TRISO coated particle fuel mixture, an electric current is passed directly through the die, with the die becoming a heating element. Pressure is applied during the sintering, which can lead to the cracking and failure of the TRISO coated particle fuel. Also, this method is very expensive due to the large amount of power required.

[0007] Binder jetting is a 3D-printing process that is used to form a hollow shell by using a nozzle to inject a binding material, usually a wax, to create shapes that are built up in layers in a bed of powder. The hollow shell is then filled with a mixture of TRISO coated particle fuel with powders. . The created shape is typically very porous and cannot be sintered, and so the porous body is then chemical vapour infiltrated with silicon carbide. However, gas flow into closed pores, and even pores deep inside the fuel product, is not possible, and so densification in the centre of the fuel product is limited whilst the outside of the fuel product is coated. This results in a fuel product with poor thermal performance, which can lead to cracking and failure.

[0008] Reactive melt infiltration is another process that may be used to form a fuel product. However, typically, use of this process may result in residual silicon or other non-ceramic material within the product.

[0009] Alternative core particles to TRISO coated particle fuel may form part of encapsulated products for use in other applications. For example, such encapsulated products may be useful in fusion, nuclear medicine and nuclear waste applications. Encapsulated products of the type described herein may also be useful in high temperature industrial processes or in applications whereby the encapsulated products are exposed to extreme temperatures and conditions.

[0010] Hence, it is desirable to provide a method of forming an encapsulated product that is simple, low-cost and avoids damaging fragile core particles, for example the fragile fuel particles.Summary

[0011] According to the present invention there is provided a method and product as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

[0012] According to an aspect of the invention, there is provided a method of forming an encapsulated product, comprising: forming a mixture of core particles and a non-oxide ceramic material, infiltrating the mixture with a fluid polymer, and heating the infiltrated mixture to form the encapsulated product.

[0013] The infiltration of the fluid polymer may fill voids in the mixture and bind the non-oxide ceramic material together, to provide an encapsulated product having a high-density matrix of non-oxide ceramic material containing the core particles, with high thermal conductivity. The non-oxide ceramic material may be provided as a slurry ora powder. The encapsulated product may be a particle containing product, which may have a more uniform distribution of particles as compared to, for example, a hot-pressed product or a fibre-reinforced composite. The encapsulated product formed according to the method may have an improved consistency in density throughout the product. The encapsulated product may have low permeability, thereby preventing coolant ingress in use.

[0014] The infiltration of the fluid polymer may allow the encapsulated product to be formed through a low temperature process relative to sintering, which may avoid damage to the core particle.

[0015] The method may be a method of forming a fuel product for a nuclear reactor, and the encapsulated product contains fuel particles. In these examples, the core particles may be fuel particles, for example coated particle fuel. The term “Coated Particle Fuel”, CPF, is a term that refers to types of small particles which may be encapsulated. Small particles may refer to particles of around 1mm in diameter. Examples of such particles may include TRISO coated particle fuel, BISO coated particle fuel, and QUADRISO coated particle fuel. It would be understood that the present disclosure may relate to other variants of CPFs in addition to the above-named examples.

[0016] The encapsulated product may be a fuel product, which may also be referred to as a fuel pellet or fuel pebble. In examples, fuel pellets may be shaped as a cylinder, or a cylinder with a hole through its central axis. In examples, fuel pebbles may be shaped as spheres or approximate spheres. The resultant fuel product is a particle-containing fuel product, for example a particle-containing fuel pellet or a particle-containing fuel pebble.

[0017] The fuel particles may be TRISO coated particle fuel, for example for use in a high-temperature gas-cooled reactor, and the heating may comprise heating the infiltrated mixture to a temperature of less than 1800°C, preferably less than or equal to 1600°C. The limit that TRISO particles can withstand is typically 1800°C above which the SiC layer begins to degrade by grain growth, whereas existing methods that include sintering silicon carbide require a sintering temperature of greater than or equal to 2000°C. In examples, the coated fuel particles may have alternative structures such as BISO or QUADRISO coated particle fuels. In other examples, zirconium carbide may be provided as a non-oxide ceramic coating material.

[0018] An advantage of the fuel pellets herein is that they are much more robust than other available designs. Suitably, the pellets are proliferation resistant, because it is very hard to gethazardous nuclear material out of them for weapons purposes; they are also safe for space missions as they will survive a chemical explosion on a launch rocket; and they be robust on geological timescales and so are a suitable final waste-form for geological disposal.

[0019] The method may further comprise infiltrating the encapsulated product with fluid polymer and heat treating the encapsulated product. The method may comprise repeating the step of infiltrating the encapsulated product with fluid polymer and heat treating the encapsulated product. The repeating of the infiltrating with fluid polymer and heat treating may improve the density of the encapsulated product, thereby providing an encapsulated product in which the core particles are more resistant to damage. This may be particularly advantageous in examples where the core particles are fuel particles, such that the fuel product has improved density. This means that the fuel product can withstand harsher temperature and pressure conditions and is more resistant to damage. In examples, one or both steps may be repeated between two and ten times. In examples, one or both steps may be repeated more than ten times.

[0020] Infiltrating the encapsulated product may comprise injecting the fluid polymer into the mixture under pressure. This may densify the fuel product. In examples, this may be through the use of hydrostatic pressure. In examples, the hydrostatic pressure applied may preferably be less than 6 bar. In examples, the applied pressure may preferably be between 1 to 6 bar. The use of hydrostatic pressure may ensure that the core particles are evenly distributed through the encapsulated product. In the present method, injecting the fluid polymer into the mixture under pressure may comprise applying a positive pressure. For the avoidance of doubt, ‘positive pressure’ as used herein is taken to mean applying a greater pressure than the nominal environmental pressure. Advantageously, in examples where the core particles are fuel particles, this may ensure that fuel particles are not in direct contact with each other, which may reduce damage to the fuel particles. This may be particularly advantageous for CPFs which may be fragile. The non-oxide material may be a powder. The fluid polymer may be a pre-ceramic polymer, for example polycarbosilane. Use of a pre-ceramic polymer may advantageously densify the fuel product. The non-oxide ceramic material may be a non-oxide ceramic powder, for example silicon carbide powder. Infiltrating the mixture and heating the mixture may cause the pre-ceramic polymer to bind the silicon carbide powder together and convert into silicon carbide. In examples, the non-oxide ceramic powder may comprise carbon powder and phenolic resin. This may yield a carbon matrix, which may have desirable thermal properties. According to other examples, the non-oxide ceramic powder may be zirconium diboride / carbide and hafnium diboride / carbide, optionally with minor additions of tungsten and / or SiC.

[0021] In examples, the fluid polymer may be replaced with a sol-gel, which is a liquid that may form ceramics like alumina and zirconia during heat treatment.

[0022] Forming the mixture may comprise mixing the core particles in a non-oxide ceramic powder, or slurry or gel containing the non-oxide ceramic powder. The slurry may be an aqueous slurry (i.e. a water-based suspension). In examples, forming the mixture may comprise mixing fuel particles in a slurry or gel containing the non-oxide ceramic power. In examples, the core particles may be added to raw powder in a mould, and pressure infiltrated. In these examples, debinding of a slurry or gel is not required. In examples, the slurry may comprise at least one kind of binder additive and a dispersant. In examples, the binder additives are a type of polymer, in particular polymers belonging to the alcohol family of organic compounds (for example, an ethylene-based polymer).

[0023] In examples, the method may comprise an optional pressing step, to compact raw power and / or compress the slurry or gel. Advantageously, this may ensure that it has filled more or all voids.

[0024] The method may further comprise drying and shaping the mixture prior to infiltrating with the fluid polymer. The method may comprise shaping the mixture into a predetermined shape, for example a pellet. The pellet may be cylindrical, annular, pebble-shaped or may take any other suitable geometry. Shaping the mixture may comprise casting the mixture into a mould. Alternatively, shaping the mixture may comprise 3D printing the mixture into a shape. In examples, drying and shaping the mixture may happen simultaneously or as separate steps. For example, the mixture may be partially dried, then shaped and then fully dried.

[0025] The slurry may comprise a binder and / or plasticiser additive. The binder and / or additive may be a polymer, for example a polymer belonging to the alcohol family of organic compounds, for example, an ethylene-based polymer. After mixing the core particles in a slurry comprising a binder additive, the mixture may have a compliance to it, which may make it easier to demould and may increase durability after demoulding. In examples where the core particles are fuel particles, this may mean that the fuel product may be more readily shaped.

[0026] The method may further comprise a de-bind and pre-sinter step prior to infiltrating the mixture with the fluid polymer. The de-bind and pre-sinter step may comprise a heat treatment for removing the binder from the mixture.

[0027] The method may further comprise overcoating the encapsulated product. Overcoating the encapsulated product may comprise overcoating the encapsulated product with a non-oxide composition. The non-oxide composition may be silicon carbide. The overcoating the encapsulated product may be performed by, for example, chemical vapour deposition. Overcoating the encapsulated product may seal the encapsulated product. In examples where the encapsulated product is a fuel product, this may advantageously seal the fuel product. This may prevent leakage of fuel particles.

[0028] The method may comprise coating the core particles prior to forming the mixture. Coating the core particles may comprise coating the fuel particles with a nano-slurry. Coating the core particles may improve the consistency of the distribution of the core particles in the mixture and may reduce the likelihood of fuel particles being in contact with each other in the encapsulated product. In examples, the core particles may be fuel particles and coating the fuel particles in this may improve the distribution of the fuel particles throughout the fuel product, which may reduce damage to fuel particles therein. For example, this may prevent the fuel particles from touching and cracking, which may be particularly advantageous in the case of CPFs which may be fragile.

[0029] According to an aspect, there is provided an encapsulated produced formed according to the method described herein. The encapsulated product may be a fuel product.

[0030] By use of the method described herein, the provided encapsulated product may have a high purity non-oxide ceramic material, for example silicon carbide, and a high thermal conductivity. The provided encapsulated product may further have low damage to fuel particle coatings and a homogenous matrix structure. This may therefore improve suitability for high-temperature applications, for example the use in fission reactors.

[0031] According to an aspect, there is provided an encapsulated product comprising a plurality of core particles encapsulated in a matrix of non-oxide ceramic material.

[0032] The encapsulated product may be a fuel product comprising a plurality of fuel particles encapsulated in a matrix of non-oxide ceramic material. In examples, the fuel product may have a density of greater or equal to 3.00 g / cm3, which may be greaterthan 93% density. In examples, the fuel product may have a thermal conductivity of greaterthan 30 W.mk before irradiation, and greater than 10 W.mK after irradiation. In examples, the fuel product may have a failure stress threshold of greaterthan 300MPa. There are examples of possible properties ofthe fuel product, but the fuel product may have ranges or properties that are outside of such ranges.

[0033] The plurality of fuel particles may be TRISO coated particle fuels. The non-oxide ceramic material may be silicon carbide.

[0034] The encapsulated product may comprise high-purity silicon carbide. That is, the silicon carbide may have no secondary phases or impurities such as sintering additives or silicon. This may advantageously improve thermal conductivity and resistance to damage which is important in high-temperature applications.

[0035] The encapsulated product may also have low damage to coatings of the fuel particles therein, advantageously reducing damage to the fragile core particles themselves.

[0036] The encapsulated product may have a homogenous matrix structure, such that they are suitable for use in harsh environments, for example high temperature reactor environments.

[0037] The encapsulated product may have a high thermal conductivity, which may improve suitability for use of the encapsulated product in fission reactors. For example, the high thermal conductivity may improve performance, efficiency and safety in such applications

[0038] In examples, the fuel particles may be BISO or QUADRISO coated particle fuels.

[0039] In examples, the non-oxide ceramic material may be zirconium diboride / carbide, hafnium diboride / carbide optionally further comprising (minor additions of) tungsten and / or SiC, or graphite.

[0040] Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.Brief Description of the Drawings

[0041] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which:

[0042] Figure 1 shows an example method of forming an encapsulated product;

[0043] Figure 2 shows an example method of forming a fuel product; and

[0044] Figure 3 shows an example fuel product: Fig. 3A shows a side view cross-section of an example fuel product; Fig. 3B shows a top-view cross section of the example of Fig. 3A; Fig. 3C shows a three-dimensional section of the example of Figs 3A and 3B; Fig. 3D shows a top-view cross section for an alternatively shaped fuel product.Detailed Description

[0045] As shown in figure 1 , a method 10 of forming an encapsulated product is provided. The method 10 comprises, at step 102, forming a mixture of core particles and a non-oxide ceramic material. The method 10 further comprises, at step 108, infiltrating the mixture with a fluid polymer. The method further comprises, at step 110, heating the infiltrated mixture to form the encapsulated product.

[0046] In examples, the core particles may be fuel particles that may comprise a fuel kernel and one or more coating layers. In examples, the core particles may comprise metallic components or other elements surrounded by one or more coatings.

[0047] As shown in figure 2, an example method 100 of forming a fuel product is provided. The method 100 of forming a fuel product as shown in figure 2 comprises steps that may be equally applied to the method 10 of forming an encapsulated product. That is, each step discussed with reference to figure 2 may be applied and included in a method of forming an encapsulated product comprising core particles.

[0048] With reference to figure 2, the example method 100 comprises, at step 102, forming a mixture of fuel particles and a non-oxide ceramic material. For example, the fuel particles are TRISO coated particle fuels , and the non-oxide ceramic material is a silicon carbide powder, and forming the mixture comprises forming mixing the TRISO coated particle fuel in a slurry, for example an aqueous slurry, containing silicon carbide powder. Use of a powder may advantageously mean that the fuel particles are better distributed as compared to use of fibre non-oxide ceramic materials. Further, by providing a SiC slurry or powder in the method, a further reaction to obtain silicon carbide from raw silicon and carbon is not required, thereby improving efficiency of the process.

[0049] In examples, the fuel within the TRISO coated particle fuel may comprise, for example, low-enriched uranium (LEU) which may contain 3-5% Uranium-235. In examples, the fuel may comprise high-assay, low-enriched uranium (HALEU) which may contain 5-20% Uranium-235. Use of HALEU may be made possible by using TRISO particles and micro-encapsulation in a fuel product, due to the enhanced fuel safety provided.

[0050] The method may comprise, at step 104, drying and shaping the mixture. For example, the mixture may be cast into a mould or may be 3D printed into a shape. In examples, step 104 comprises shaping the mixture, and then drying the mixture.

[0051] In examples, the shaping may be provided by casting the mixture into a mould and drying the mixture within the mould. In examples, the mixture may be provided in a mould to form a cylindrical pellet. This may advantageously be a simple and cost-effective process. In examples, the mixture may be 3D printed to form complex geometries in the resultant product. For example, the mixture may be 3D printed to form complex geometries via robo-casting, or robotic material extrusion. Advantageously, this may allow for products to be provided in more complex shapes, as required. In examples, binder jetting may be used to shape the mixture.

[0052] In examples, drying and shaping the mixture at step 104 is done simultaneously. In examples, the method 100 may comprise separate steps of drying the mixture, then shaping the mixture. In examples, the method 100 may comprise partial drying of the mixture, then shapingof the mixture, then complete drying of the mixture. In examples, the method 100 may comprise shaping the mixture before drying the mixture.

[0053] Optionally, the mixture may comprise a binder additive, for example a type of polymer, in particular a polymer belonging to the alcohol family of organic compounds, for example, an ethylene-based polymer. In examples, the binder additive is added to the mixture during step 102. In examples, the binder additive may be added to the mixture after forming the mixture of fuel particles and non-oxide ceramic material at step 102 but before the dry and / or shaping of the mixture at step 104.

[0054] In examples where the mixture comprises a binder additive, the method may comprise, at step 106, de-binding the mixture to remove polymers that may be still left over from the slurry phase. De-binding the mixture may comprise heat-treating the mixture. In examples, de-binding the mixture may comprise de-binding using solvents or catalysts.

[0055] In examples, the core particles may be added to raw powder in a mould, i.e. not provided in a slurry or gel. In this example, the core particles in the raw powder may be pressure infiltrated. In these examples, debinding of a slurry or gel is not required. In this example, binder jetting may be used on the powder for shaping. This may comprise using molten wax or polymer to bind particles in a powder bed together in a layer, whereby any unbound powder is removed after shaping.

[0056] In examples, the method may comprise an optional pressing step, to compact raw power and / or compress the slurry or gel. Advantageously, this may unsure that it has filled more or all voids to improve density.

[0057] The method may additionally or alternatively comprise, at step 106, pre-sintering the mixture. Pre-sintering may be carried out by heat-treating the mixture.

[0058] In examples, pre-sintering may be carried out before de-binding of the mixture. That is, pre-sintering may be carried out before further heating to de-bind the mixture. In examples, presintering and de-binding may be carried out simultaneously.

[0059] Notably, the slurry may not comprise any other additives that are typically used in a hot-pressing process and which corrode in water environments. The fuel product produced according to the method thereby comprises a high-purity ceramic matrix. In the method 10 of forming an encapsulated product, the resultant encapsulated product may comprise a high-purity ceramic matrix.

[0060] The method comprises, at step 108, infiltrating the mixture with a fluid polymer. The mixture may be infiltrated with the fluid polymer under pressure, which may force the fluid polymer into voids in the mixture.

[0061] In an example, the fluid polymer may be pre-heated to reduce its viscosity prior to infiltration. For example, the polymer may be heated to about 60 degrees C, and then injected by applying positive pressure. The pressure is preferably about less than 6 bar. In examples the pressure may be greater than 1 bar but less than 6 bar. In examples, the pressure may be between 4 bar and 6 bar. It will be appreciated that different pressures may be used based on the degree of pre-heating.

[0062] The method comprises, at step 110, heating the infiltrated mixture, for example in a furnace or heating chamber. In examples, heating may be by pyrolysis. In examples, heating may be microwave heating or RF heating. In examples, other heating methods may be used, for example by a gasification process, or by direct heat treatment. The heating may comprise heating the infiltrated mixture firstly at a temperature of around 200-300°C, then at a temperature of around 800-1000°C and then at a temperature of between 1410-1600°C. In examples, the heating may comprise heating the infiltrated mixture to a temperature of less than 1800°C, preferably less than or equal to 1600°C.

[0063] Optionally, the method may comprise repeating steps 108 and 110 to further densify the fuel product. Steps 108 and 110 may be repeated multiple times, for example two, three or four times. In examples, one or both of steps 108 and 110 may be repeated one or more times. In examples, only step 108 may be repeated. In examples, step 110 may be repeated. In examples, one of steps 108 or 110 may be repeated more times than the other of steps 108 or 110.

[0064] In examples, the method may further comprise, at step 112, coating the fuel product using a non-oxide composition, for example SiC. The fuel product may be coated by chemical vapour deposition. Advantageously, chemical vapour deposition provides for high-quality nonoxide composition coating and is highly scalable. In examples, the fuel product may be coated by a different coating technical, for example but not limited to: physical vapour deposition; atomic layer deposition; spray pyrolysis; electromechanical deposition; electrochemical deposition; dip coating.

[0065] In examples, the method may comprise coating the fuel particles with a nano-slurry before mixing into the mixture at step 102. Advantageously, this may improve consistency in distribution of fuel particles in the mixture. It may also help to ensure that fuel particles are not in direct contact, thereby reducing the likelihood of damage.

[0066] An overview of an example method comprising some are all of the steps discussed herein may comprise:

[0067] Firstly, providing TRISO coated particle fuel, which may optionally be overcoated, and mixing with powder or powder-containing slurry. The mixture may be poured into a mould. The optional debind and pre-sinter steps may be carried out. A fluid polymer may be infiltrated into the mixture, optionally at a pressure of up to 6 bar. During or after infiltration, the mixture may be heated in a furnace or heating chamber at a temperature of between 200-300C. The fuel product may be demoulded and placed in a furnace to be heat-treated at 800-1000C for ceramisation. The heating may be repeated several, for example two to four times.

[0068] Figure 3 shows various views of a fuel product 200 formed according to the method 100. The fuel product 200 shown in figure 3 comprises a plurality of fuel particles 202 encapsulated within a matrix of non-oxide ceramic material 204. The fuel product 204 is overcoated with a non-oxide material. The fuel product 200 has a diameter of 2-3 centimetres, whilst the diameter of the fuel particles is approximately a millimetre. The overcoat may have a thickness of between 100 and 150 microns.

[0069] The fuel product 200 is an exemplary embodiment. The features of the fuel product 200 described herein may equally be part of an encapsulated product formed with alternate core particles to the example fuel particles 202. For example, the core particles may comprise lithium oxide, for example with a porous lithium ceramic matrix.

[0070] The fuel product 200 may be cylindrical in shape. In examples, the fuel product 200 annular, pebble-shaped, or other suitable alternative geometries.

[0071] The fuel product 200 is a high-density fuel element matrix. The fuel product may have a density of greater or equal to 3.00 g / cm3, which may be greater than 93% density.

[0072] The high-density fuel element provides high thermal conductivity. The fuel product may have a thermal conductivity of greater than 30 W.mk before irradiation, and greater than 10 W.mK after irradiation. The fuel product 200 is a low permeation material. For use in a nuclear reactor, this means that the fuel product advantageously provides fission product containment and prevents coolant ingress.

[0073] The fuel product 200 may have fuel particles which are evenly distributed and not in direct contact with each other. This reduces risk of damage to the fuel particles

[0074] Also provided may be the fuel product formed according to the method 10, wherein the fuel particles are TRISO coated particle fuel, and the non-oxide ceramic material is silicon carbide, may be used in a nuclear fission reactor, in particular a high-temperature gas-cooled reactor.

[0075] In examples, there may be provided the encapsulated product formed according to method 10 for use in fusion applications. This may be in the form of 3D printed Li ceramic structures containing Li2O particles.

[0076] Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of others.

[0077] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0078] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0079] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0080] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS1. A method of forming an encapsulated product, the method comprising:forming a mixture of core particles and a non-oxide ceramic material,infiltrating the mixture with a fluid polymer, andheating the infiltrated mixture to form the encapsulated product.

2. The method of claim 1 , further comprising infiltrating the encapsulated product with fluid polymer and heat treating the product.

3. The method of claim 2, further comprising repeating the step of infiltrating the encapsulated product with fluid polymer and heating the encapsulated product.

4. The method according to any preceding claim, wherein the infiltrating with the fluid polymer is performed using hydrostatic pressure.

5. The method of any preceding claim, wherein the non-oxide material is a powder.

6. The method of claim 5, wherein forming the mixture comprises mixing the core particles in a non-oxide powder, ora slurry or gel containing the non-oxide ceramic powder.

7. The method of claim 6, further comprising drying and shaping the mixture prior to infiltrating with the fluid polymer.

8. The method of claim 7, wherein the shaping comprises casting the mixture into a mould or 3D printing the mixture into a shape.

9. The method of any of claims 6 to 8, wherein the slurry comprises a binder additive, and wherein the method further comprises a de-bind and pre-sinter step prior to infiltrating with the fluid polymer.

10. The method of any of claims 5 to 9, wherein the fluid polymer is a pre-ceramic polymer.

11. The method of claim 10, wherein heating the infiltrated mixture comprises converting the fluid polymer into a non-oxide ceramic and binding the non-oxide ceramic powder.

12. The method of any preceding claim, wherein the non-oxide ceramic material is silicon carbide.

13. The method of any preceding claim, wherein the method is a method for forming a fuel product for a nuclear reactor, and wherein the core particles are fuel particles.

14. The method of claim 13, wherein the fuel particles are TRISO coated particle fuel, and the fuel product is a fuel product for a fission reactor.

15. The method of claim 14, wherein heating the infiltrated mixture comprises heating the mixture to a temperature less than 1800°C, preferably less than or equal to 1600°C.

16. The method of any preceding claim, further comprising coating the core particles prior to forming the mixture.

17. The method of any preceding claim, wherein the method further comprises overcoating the encapsulated product.

18. The method of claim 17, wherein overcoating the fuel product comprises overcoating the encapsulated product with silicon carbide by vapour deposition.

19. An encapsulated product formed according to the method of any preceding claim.

20. The encapsulated product of claim 19, wherein the encapsulated product is a fuel product.

21. Use of the fuel product of claim 20 in a fission reactor.

22. An encapsulated product comprising a plurality of core particles encapsulated in a matrix of non-oxide ceramic material.

23. The encapsulated product of claim 22, wherein the plurality of core particles are fuel particles.

24. The encapsulated product according to claim 23, wherein the plurality of fuel particles are TRISO coated particle fuel and the non-oxide ceramic material is silicon carbide.

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