GB2638092A

GB2638092A - Nuclear Fuel Kernel Manufacture

Info

Publication number: GB2638092A
Application number: GB2503580.9A
Authority: GB
Inventors: N Leech Owen; Middleburgh Simon; Mohun Ritesh; Makurunje Phylis
Original assignee: Rolls Royce Submarines Ltd
Current assignee: Rolls Royce Submarines Ltd
Priority date: 2025-03-12
Filing date: 2025-03-12
Publication date: 2025-08-13
Also published as: GB202503580D0

Abstract

A system 10 for manufacturing uranic nuclear fuel kernels 15 has a spray drying chamber 20 connected to a filtration chamber 30 by an interconnecting feed pipe 40. The spray drying chamber 20 has a fuel broth inlet 23, a hot gas inlet 24, and a gaseous reagent inlet 25 that are oriented so that droplets of the fuel broth 23a interact with hot gas 24a and gaseous reagent 25a to form gel-bound particles. The filtration chamber 30 has a cyclone generator 33 that is configured to swirl the gel-bound particles received from the bottom 22 of the spray drying chamber to form uranic nuclear fuel kernels that are dispensable from a fuel kernel outlet 34. The fuel broth may comprise a mixture of a uranic material, e.g. uranium dioxide, uranium carbide, and a gelling agent, e.g. sodium alginate.

Description

NUCLEAR FUEL KERNEL MANUFACTURE

FIELD

This disclosure relates to a system and a method for manufacturing nuclear fuel kernels for use in nuclear reactors, e.g. nuclear fuel kernels for tristructuralisotropic (TRISO) fuels used in advanced modular nuclear reactors.

BACKGROUND

o Nuclear reactors have been used for many years to generate electricity from the heat that is released when isotopes of certain elements, e.g. uranium-235 or plutonium-239, are split. The heat is generally used to heat water that creates steam, which is then used to turn an electrical generator that produces the electricity.

More recently small modular reactors (SMRs) have been developed to safely generate power with a significantly reduced footprint.

Advanced modular nuclear reactors are being considered for a number of purposes, both terrestrial and extra-terrestrial, owing to their compact nature, portability, and zero carbon footprint. Consequently, fuels suitable for use in nuclear microreactors and advanced modular reactors are also of interest. One fuel type in particular, TRISO (TRi-structural Isotropic) coated particles, is of considerable interest, owing to its robust nature and self-containment of fission products. TRISO particles comprise a uranium oxide fuel kernel surrounded by four coatings: from inside to outside a porous graphite coating, a high density graphite coating, a silicon carbide coating, and an outer high density graphite coating. The diameter of the uranium-oxide kernel is about 1 mm.

The current industry standard method for producing uranium dioxide fuel kernels is to use a wet chemistry method known as uranyl nitrate sol-gel. In that method, uranium dioxide is dissolved in nitric acid and combined with other chemicals to form a broth solution of uranyl nitrate. This uranyl nitrate broth is then formed into droplets, e.g. by being forced through a vibrating nozzle, which then fall into a column filled with a liquid reagent that causes droplets of the uranyl nitrate broth to form spherical semi-solid kernels. These kernels are then washed, dried, and heat-treated.

This method has several limitations that diminish its suitability to be employed in the manufacture of nuclear fuel kernels for use in advanced modular reactor. It is suited to lab-scale batch production rather than commercial production particularly on a continuous basis.

Instead of creating balls via a trickling single-droplet stream, spray drying forms multiple streams of fast-moving droplets. While spray drying has been investigated in the uranic fuels manufacturing processes, it has previously been used as a method for drying liquid streams e.g. of yellow cake, or forming soft microspheres (agglomerates) for uniaxial pressing. To manufacture nuclear fuel kernels on a continuous basis, however it does not provide kernels with the tight density requirements for use in advanced modular reactors. Without modification, It also tends to produce microspheres that might disintegrate to form a powder creating waste.

There is therefore a need for an improved system and method for manufacturing nuclear fuel kernels, which can produce robust, highly spherical kernels at a rate and on a scale suitable for the expected market demand, or at least provides a useful alternative to o known systems and methods for manufacturing nuclear fuel kernels.

SUMMARY

In a first aspect, there is provided a system for manufacturing uranic nuclear fuel kernels, the system comprises: a spray drying chamber that has a spray drying chamber top portion and a spray drying chamber bottom portion; a filtration chamber that has a filtration chamber top portion and a filtration chamber bottom portion; and a feed pipe that connects the spray drying chamber bottom portion of the spray drying chamber and the filtration chamber top portion of the filtration chamber; the spray drying chamber comprising: a fuel broth inlet configured to supply a fuel broth in the form of droplets from a supply of fuel broth into the spray drying chamber top portion of the spray drying chamber; a hot gas inlet configured to supply a hot gas from a supply of hot gas into the spray drying chamber top portion of the spray drying chamber; and a gaseous reagent inlet configured to supply a gaseous reagent from a supply of gaseous reagent into the spray drying chamber top portion of the spray drying chamber; the fuel broth inlet, the hot gas inlet and the gaseous reagent inlet being oriented so that the droplets of fuel broth interact with the hot gas and the gaseous reagent to form gel-bound particles; and the filtration chamber has a cyclone generator that is configured to swirl the gel-bound particles received from the spray drying chamber bottom portion of the spray drying chamber and form uranic nuclear fuel kernels that are dispensable from a fuel kernel outlet that is formed in the filtration chamber bottom portion of the filtration chamber.

In some embodiments, the hot gas inlet and the gaseous reagent inlet are integrated.

In some embodiments, the fuel broth comprises a mixture of a uranic material and a gelling agent.

In some embodiments, the uranic material is uranium dioxide (UO2), uranium carbide (UCO), or a mixture of uranium carbide and uranium-plutonium carbide (UPuC). In some embodiments, the fuel broth further comprises carbon black.

In some embodiments, the gelling agent is sodium alginate.

In some embodiments, the hot gas is air, argon or nitrogen or a mixture thereof.

In some embodiments, the gaseous reagent is ammonium chloride.

In some embodiments, a dust vent is formed in the filtration chamber top portion of the filtration chamber.

In a second aspect, there is provided a method for manufacturing uranic nuclear fuel kernels, the method comprising the steps of: bringing one or more streams of a hot gas and one or more streams of a gaseous reagent into contact with droplets of a fuel broth in a spray drying chamber top portion of a spray drying chamber to form a spray of hot droplets, the fuel broth comprising a uranic material and a gelling agent; allowing the hot spray droplets to pass down through the spray drying chamber so they cool, gelate and solidify to form dried gel-bound particles; passing the dried gel-bound particles through a filtration chamber to separate the dried gel-bound particles by mass; and collecting the dried gel-bound particles of a desired size range as uranic nuclear fuel is kernels.

In some embodiments, the hot gas and the gaseous reagent are mixed together before being brought into contact with the droplets of fuel broth.

In some embodiments, the desired size range of the uranic nuclear fuel kernels is from 200 to 1000 pm in diameter.

In some embodiments, the uranic material in the fuel broth is selected from uranium dioxide, uranium carbide, or a mixture of uranium carbide and uranium-plutonium carbide; the gelling agent in the fuel broth is sodium alginate; the hot gas is air, argon or nitrogen or a mixture thereof; and the gaseous reagent is ammonium chloride.

In some embodiments, the fuel broth comprises uranium dioxide, carbon black and sodium alginate; the hot gas is air; and the gaseous reagent is ammonium chloride.

In some embodiments, the droplets of a fuel broth are brought into contact with a coating broth that comprises graphite and alginate upon entering the spray drying chamber to form coated nuclear particles that comprise uranic nuclear fuel kernels encapsulated with a porous graphite coating.

In a third aspect, there is provided a method for manufacturing tristructural-isotropic particle nuclear fuel, the method comprising the steps of: manufacturing uranic nuclear fuel kernels according to the method of the second aspect; encapsulating the uranic nuclear fuel kernels within a porous graphite coating; subsequently applying a high density graphite coating; subsequently applying a silicon carbide coating; and subsequently applying an outer high density graphite coating to form a tristructural-isotropic particle nuclear fuel.

In some embodiments, the porous graphite coating, the high density graphite coating, the silicon carbide coating, and the outer high density graphite coating are applied by chemical vapor deposition.

Throughout this specification, including the claims which follow, unless the context s requires otherwise, the word "comprise" and "include", and variations such as "comprises", "comprising", and "including" will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The term "configured to" and like as used herein is at least as restrictive as the term "adapted to" and requires actual design intention to perform the specified function rather than mere physical capability of performing such a function.

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

The term "uranic nuclear fuel kernel" as used herein means a mass of uranic based fissile material that may form the central component of a particle of a nuclear fuel. Such uranic nuclear fuel kernels are typically at least substantially spherical and the size of a poppy seed. They may form the central component of tristructural-isotropic particle nuclear fuels.

The term "tristructural-isotropic particle nuclear fuel" or "TRISO particle nuclear fuel" as used herein means fissile particles that are used by a nuclear power station or a nuclear power plant, e.g. of a nuclear powered submarine, to generate energy that comprises a uranium oxide nuclear fuel kernel that is surrounded by four coatings: from inside to outside, a porous graphite coating, a high density graphite coating, a silicon carbide coating, and an outer high density graphite coating.

The term "uranium dioxide" or "UO2" (aka uranium(IV) oxide, urania and uranous oxide) as used herein means an oxide of uranium. It typically exists as a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. The compound is used in nuclear fuel rods in nuclear reactors in processed form.

The term "uranium oxycarbide" or "UCO" as used herein means a mixture of uranium oxide and uranium carbide. Uranium carbide is a hard refractory ceramic material that exists in several stoichiometries such as uranium methanide (UC), uranium sesquicarbide (U2C3), uranium acetylide (UC2). The compound is used as a nuclear fuel for nuclear reactors, typically in the form of pellets or tablets, e.g. as an alternative to uranium dioxide in order to mitigate the undesirable formation and release of carbon monoxide gas in such reactors.

The term "plutonium carbide" or "PuC" as used herein means a carbide of plutonium. It can be used as a nuclear fuel for nuclear reactors and exists in several stoichiometries including PuC and Pu2C3. It may be used in conjunction with uranium carbide, i.e. as uranium-plutonium carbide (UPuC).

The term "alginate" (aka algin) as used herein means a salt of alginic acid or a derivative of alginic acid. Alginate is present in the cell walls of brown algae as the calcium, magnesium and sodium salts of alginic acid. It is soluble in water at room o temperature and reacts with divalent metals ions to form a gel.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described by way of example only with reference to the accompanying drawings, in which: FIG. 1 schematically represents a first embodiment of the system for manufacturing uranic nuclear fuel kernels of the present disclosure; FIG. 2 schematically represents a second embodiment of the system for manufacturing uranic nuclear fuel kernels of the present disclosure; FIG. 3 is a flow chart of the method for manufacturing uranic nuclear fuel kernels

of the present disclosure;

FIG. 4 schematically represents a first embodiment of the system for manufacturing coated uranic nuclear fuel kernels of the present disclosure; FIG. 5 schematically represents a tristructural-isotropic nuclear fuel particle that has a uranic nuclear fuel kernel at its core.

FIG. 6 is a flow chart of the method for manufacturing tristructural-isotropic particle

nuclear fuel of the present disclosure.

The following table lists the reference numerals used in the drawings with the features to which they refer: Ref no. Feature FIG. System for manufacturing uranic nuclear fuel kernels 1 2 11 System for manufacturing coated uranic nuclear fuel particles 4 Uranic nuclear fuel kernel 1 2 4 18 Coated uranic nuclear fuel particle 4 Spray drying chamber 1 2 4 21 Spray drying chamber top portion 1 2 4 21a Spray drying chamber top 1 2 4 22 Spray drying chamber bottom portion 1 2 4 Ref no. Feature FIG. 23 Fuel broth inlet 1 24 23a Fuel broth 1 2 4 23b Supply of fuel broth 1 2 4 24 Hot gas inlet 1 4 24a Hot gas 1 2 4 24b Supply of hot gas 1 2 4 Gaseous reagent inlet 1 4 25a Gaseous reagent 1 2 4 25b Supply of gaseous reagent 1 2 4 26 Common inlet 2 27 Coating broth inlet 4 27a Coating broth 4 27b Supply of coating broth 4 28 Arrow (direction of droplet flow and progress of transformation) 1 2 4 Filtration chamber 1 2 4 31 Filtration chamber top portion 1 2 4 32 Filtration chamber bottom portion 1 2 4 33 Cyclone generator 1 2 4 34 Fuel kernel outlet 1 2 4 Feed pipe 1 2 4 Dust vent 1 2 4 TRISO nuclear fuel particle 5 61 Porous graphite coating 4 5 62 High density graphite coating 5 63 Silicon carbide coating 5 64 Outer high density graphite coating 5 Method for manufacturing uranic nuclear fuel kernels 3 101 Step 3 102 Step 3 103 Step 3 104 Step 3 Method for manufacturing tristructural-isotropic (TRISO) nuclear fuel 6 201 Step 6 202 Step 6 203 Step 6 204 Step 6 205 Step 6

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.

The present disclosure provides a system and a method for manufacturing nuclear fuel kernels, e.g. nuclear fuel kernels for tristructural-isotropic (TRISO) particle nuclear fuels used in advanced modular nuclear reactors. The present disclosure also provides a system and a method for manufacturing the relevant layers of tristructural-isotropic (TRISO) particle nuclear fuel.

As mentioned above, TRISO particle nuclear fuels comprise particles that comprise a uranium oxide fuel kernel surrounded by four coatings: from inside to outside, a porous graphite coating, a high density graphite coating, a silicon carbide coating, and an outer high density graphite coating. In contrast, conventional nuclear fuels typically comprise centimetre sized pellets of uranium dioxide that are enclosed in four meter-long is zirconium alloy tubes. Giving each millimetre sized piece of TRISO particle fuel nuclear fuel its own containment and pressure vessel, significantly enhances the ability of that fuel to contain fission products, even up to very high temperatures at which conventional nuclear fuels would melt or fail. Another benefit of using TRISO particle fuel nuclear fuel is that it can be used to power nuclear reactors that are much smaller than nuclear reactors that are powered by conventional nuclear fuels.

The system and method for manufacturing nuclear fuel kernels of the present disclosure combines spray drying and gel casting technologies. Spray drying involves forming a dry powder from a liquid or a slurry by rapidly drying with a hot gas. Spray drying produces particles of varied sizes, typically between 200 and 800 microns in diameter. Gel casting involves forming a slurry of a monomer, a cross linker, a free radical initiator or a catalyst, and forming the slurry to form ceramic or polymeric particles. The particles typically have consistent and larger particle sizes than spray drying, typically 200 up to a few millimetres.

FIG.1 is a schematic representation of a first embodiment of a system 10 for manufacturing uranic nuclear fuel kernels 15. The system 10 employs a combination of spray drying technology and gel casting technology. The system has a spray drying chamber 20 that is connected to filtration chamber 30 via a feed pipe 40.

The spray drying chamber 20 can take in suitable form for its purpose. It is typically substantially cylindrical and vertically elongated in shape to accommodate the spray drying and gel formation processes that it houses. As shown in FIG. 1, the spray drying chamber 20 has a spray drying chamber top portion 21 and a spray drying chamber bottom portion 22.

A fuel broth inlet 23 is formed in the spray drying chamber top portion 21 of the spray drying chamber 20. The fuel broth inlet 23 is configured to supply a fuel broth 23a into the spray drying chamber 20 from a supply of fuel broth 23b. In the embodiment shown, the fuel broth inlet 23 is located on a spray drying chamber top 21a of the spray s drying chamber 20. More particularly, the fuel broth inlet 23 is located at a substantially central position on the spray drying chamber top 21a to maximise the volume over which the fuel broth 23a is sprayed into the spray drying chamber 20. The system is configured to be able to supply the fuel broth 23a into the spray drying chamber 20 on a static, dynamic or continuous basis. The supply may be regulated by a suitable control system (not shown) that includes a controller (not shown). Sensors (not shown) may be provided to monitor various process parameters such as temperature, pressure, and particle flow, for control, production efficiency, and safety purposes.

The fuel broth may be supplied into the spray drying chamber 20 as droplets. These droplets may be formed in various ways that are known in the art, including direct/unassisted droplet casting, electrostatic-enhanced dropping, nozzle vibration, nozzle or disc rotation, and jet-cutting.

The fuel broth 23a provides the uranic material of the uranic nuclear fuel kernels that are manufactured by the method of the present disclosure. The fuel broth can have any suitable formulation for its purpose. It typically comprises a mixture of a uranic material and a gelling agent. The fuel broth might also comprise a source of carbon and/or one or more binders, dispersants or pH modifiers.

The uranic material may be uranium dioxide (UO2), U306, UO3, uranium carbide and its various stoichiometries, or a mixture of uranium oxide and uranium carbide (UCO), or a mixture of uranium carbide and uranium-plutonium carbide (UPuC).

When the uranic material includes uranium carbide and/or uranium-plutonium carbide, the uranium carbide and/or uranium-plutonium carbide provides a source of carbon. When another or an additional source of carbon is desired, it can take many forms e.g. carbon black (aka acetylene black).

The gelling agent may be sodium alginate, which is a natural polysaccharide that is typically extracted from kelp or sargassum of brown algae. It may also be agarose or gelatin. The gelling agent reacts with the uranic material in the fuel broth to form a colloid. It can form 1 to 10% by weight of the fuel broth.

In some embodiments, the fuel broth is a mixture of uranium dioxide (UO2) and sodium alginate. The sodium alginate may form 1 to 10% by weight of the fuel broth.

As shown in FIG. 1, a hot gas inlet 24 is formed in the spray drying chamber top portion 21 of the spray drying chamber 20. The hot gas inlet 24 is configured to supply one or more streams of a hot gas 24a into the spray drying chamber 20 from a supply of hot gas 24b. The hot gas inlet 24 is more particularly configured to direct the hot gas 24a into the stream of fuel broth 23a that is provided into the spray drying chamber 20 via the fuel broth inlet 23 so that the hot gas 24a contacts and reacts with the fuel broth 23a. In the embodiment shown, the hot gas inlet 24 is located on a side of the spray drying chamber and below the fuel broth inlet 23 for this purpose. The system is configured to be able to supply the hot gas 24a into the spray drying chamber 20 on a static, dynamic or continuous basis. The supply may be regulated by a suitable control system (not shown) e.g. that includes the aforementioned controller (not shown). As before, sensors (not shown) may be provided to monitor various process parameters such as temperature, pressure, and particle flow, for control, production efficiency, and safety purposes.

The hot gas 24a enables the spray drying of the fuel broth 23a in the manufacture uranic nuclear fuel kernels, i.e. fluid fuel broth 23a is transformed into dry particles. It provides energy in the form of heat, which drives the drying and gelation reactions that transform fuel broth droplets into uranic nuclear fuel kernels.

The hot gas 24a may take any suitable form for its purpose. The gas may be air, a non-reactive gas (e.g. argon or nitrogen), an inert gas (e.g. helium, argon, neon or xenon) or any mixture thereof. The gas is hot in the sense that it has a temperature when exiting the hot gas inlet that is sufficient to evaporate moisture, e.g. between 90 °C and 450 °C, but typically between 100 °C and 350 °C.

As shown in FIG. 1, a gaseous reagent inlet 25 is formed in the spray drying chamber top portion 21 of the spray drying chamber 20. The gaseous reagent inlet 25 is configured to supply one or more streams of a gaseous reagent 25a into the spray drying chamber 20 from a supply of gaseous reagent 25b. The gaseous reagent inlet 25 is more particularly configured to direct the gaseous reagent 25b into the stream of fuel broth 23a that is provided into the spray drying chamber 20 via the fuel broth inlet 23 so that the gaseous reagent 25a contacts and reacts with the fuel broth 23a. In the embodiment shown, the gaseous reagent inlet 25 is located on a side of the spray drying chamber and below the fuel broth inlet 23 for this purpose. The system is configured to be able to supply the gaseous reagent 25a into the spray drying chamber 20 on a static, dynamic or continuous basis. The supply may be regulated by a suitable control system (not shown) e.g. that includes the aforementioned controller (not shown).

The gaseous reagent 25a assists in spray drying the fuel broth 23a in the manufacture uranic nuclear fuel kernels. The gaseous reagent 25a may take any suitable form for its purpose. The gaseous reagent 25a may be ammonium chloride. When the gaseous reagent 25a is ammonium chloride, it can enable ion exchange by providing the ammonium cation that displaces the sodium cation in the sodium alginate.

The gaseous reagent 25a is gaseous as in that physical state the reagent can most effectively react with the fuel broth 23a, more specifically the gelling agent that is suspended in the fuel broth 23a, whilst hot droplets are formed in the spray drying process.

The choice of the gaseous reagent 25a may depend on the composition of the fuel broth 23a and perhaps even the choice of the hot gas 24a. When the fuel broth 23a contains an alginate salt, e.g. sodium alginate, the gaseous reagent 25a is ideally a salt that can displace the sodium salt via ion exchange. e.g. ammonium chloride. This exchange of ions typifies the gel casting aspect of the system of the present disclosure that is employed to manufacture the desired uranic nuclear fuel kernels and tristructural-isotropic particle nuclear fuel.

In some embodiments, the fuel broth 23a contains uranium dioxide (UO2), uranium carbide (UCO), or a mixture of uranium carbide and uranium-plutonium carbide (UPuC), carbon black, and sodium alginate; the hot gas 24a is air, a non-reactive gas (e.g. argon or nitrogen), an inert gas (e.g. helium, argon, neon or xenon) or any mixture thereof; and the gaseous reagent 25a is ammonium chloride.

In some embodiments, the fuel broth 23a contains uranium dioxide (UO2) and sodium alginate, and optionally various additives used in the spray drying art, e.g. one or more binders, dispersants or pH modifiers; the hot gas 24a is air or an inert or non-reactive gas; and the gaseous reagent 25a is ammonium chloride.

Bringing the hot gas 23a, and the gaseous reagent 24a into contact the fuel broth 23a within the spray drying chamber 20 as described above initially forms a spray of hot droplets and as those droplets fall within the spray drying chamber 20 they cool, gelate and solidify to form dried gel-bound particles. The cooling, gelating and solidifying occurs transitionally albeit almost instantaneously. The direction of droplet flow and the progress of the transformation is indicated by the arrow 28. The dry gel-bound particles are typically from 200 to 800 pm in diameter.

The spray drying chamber 20 is configured and dimensioned to suitably accommodate the transformation that occurs as the droplets flow through the spray drying chamber 20. For that purpose the spray drying chamber 20 is typically substantially cylindrical and vertically elongated. In some embodiments, the height of the spray drying chamber 20 is one to four times, e.g. one to three times, the diameter of the spray drying chamber 20. In some embodiments, the height of the spray drying chamber 20 is one to two to three times, e.g. 2.5 times, the diameter of the spray drying chamber 20.

As shown in FIG. 1, the dry gel-bound particles pass from the spray drying chamber 20 to a filtration chamber 30 via a feed pipe 40 that connects the spray drying chamber bottom portion 22 of the spray drying chamber and the filtration chamber top portion 31 of the filtration chamber. The filtration chamber 30 has a cyclone generator 33 that swirls the air within the filtration chamber in order to draw the dry particles into the filtration chamber 30 from the spray drying chamber 20. The feed pipe 40 connects the spray drying chamber bottom portion 22 to the filtration chamber top portion 31 so that the desired larger dry particles will fall towards the filtration chamber bottom portion 32 with gravity while the smaller dry particles or "dust" can be vented from the filtration chamber 30 via a dust vent 50 that is formed or connected in the filtration chamber top portion 31 of the filtration chamber 30.

The filtration chamber 30 can take any suitable form for its purpose. It is typically o substantially cylindrical and vertically elongated in shape to accommodate the size separation process described.

The cyclone generator 33 can take any suitable form for its purpose. For example, the cyclone generator 33 may comprise a series of angled jets or fans that are distributed around the periphery of the filtration chamber 30.

The passage of dust from the dust vent 50 may be driven or assisted by a pump (not shown). The gases may be drawn by a fan at the outlet of the spray drying set up via a cyclone system. The dust may be collected in a dust collector (not shown) and the dust collected therein may be periodically safely disposed of or recycled.

The larger dry particles are the desired uranic nuclear fuel kernels 15 manufactured by the system of the present disclosure. These will pass down through the filtration chamber 30 and exit the filtration chamber 30 via a fuel kernel outlet 34 this is formed or connected to the filtration chamber bottom portion 32 of the filtration chamber 30.

The fuel kernel outlet 34 can take any suitable form for its purpose. The composition may be determined by the powder feed. The shape is typically spherical. The particle size is typically 200 to 800 microns in diameter.

The system of the present disclosure is configured and operates so that the uranic nuclear fuel kernels 15 are at least substantially spherical. Spherical uranic nuclear fuel kernels 15 provide an ideal foundation for the porous graphite coatings, high density graphite coatings, silicon carbide coatings, and high density graphite coatings that are subsequently applied to manufacture desired tristructural-isotropic (TRISO) fuels for advanced modular nuclear reactors. The closer the uranic nuclear fuel kernels 15 are to being perfectly spherical, the closer the layers that are formed upon the uranic nuclear fuel kernels will be uniform. Highly spherical nuclear fuel kernels tend to have uniform robustness, which reduces the likelihood of microscopic defects, flaws, or imperfections, which promote weaknesses, e.g. cracking.

As mentioned above, the fuel broth 23a, the hot gas 24a and the gaseous reagent 25 may be supplied to the spray drying chamber 20 on a static, dynamic or continuous basis. Operating the system 10 on a continuous basis in particular typically enables the uranic nuclear fuel kernels 15 to be manufactured at a scale that is suitable for industrial s production.

FIG. 2 is a schematic representation of a second embodiment of a system 10 for manufacturing uranic nuclear fuel kernels 15. This second embodiment shares most of the features found in the first embodiment depicted in FIG. 1 and described above, the key difference being that in the second embodiment, the hot gas 24a and the gaseous reagent 25a are mixed prior to entering the spray drying chamber 20, and as such enter the spray drying chamber through a common inlet 26. In the embodiment depicted in FIG. 2, the hot gas supplied by the supply of hot gas 24b mixes with the gaseous reagent supplied by the supply of gaseous reagent 25b before the mixture of same enters the spray drying chamber 20 via the common inlet 26, i.e. a single inlet operates as both the hot gas inlet (24) and the gaseous reagent inlet (25). In other embodiments, the hot gas supplied by the supply of hot gas 24b and the gaseous reagent supplied by the supply of gaseous reagent 25b may mix within the common inlet 26 itself i.e. the hot gas inlet (24) and the gaseous reagent inlet (25) are integrated. Both options, suitably configured, can offer useful opportunities to control and optimise the mixing of the hot gas and the gaseous reagent before contacting the droplets of fuel broth.

FIG. 3 is a flow chart of the method 100 of the present disclosure for manufacturing uranic nuclear fuel kernels 15. Such a method may be carried out using the system depicted in FIG. 1 or FIG. 2 or as otherwise described above.

In a first step 101 of the method 100, one or more streams of a hot gas 24a and one or more streams of a gaseous reagent 25a are brought into contact with droplets of a fuel broth 23a in a spray drying chamber top portion 21 of a spray drying chamber 20 to form a spray of hot droplets, the fuel broth 23a comprising a uranic material and a gelling agent. The hot gas 24a, the gaseous reagent 25a, the fuel broth 23, the spray drying chamber 20, the uranic material, and the gelling agent may be as described above in relation to the system 10 for manufacturing uranic nuclear fuel kernels 15. The stream(s) of hot gas 24a and the stream(s) of a gaseous reagent 25a may be brought into contact with the droplets of the fuel broth 23a via separate inlets (24 and 25) or via a common or integrated inlet (26). The hot gas 24a and the gaseous reagent 25a may be mixed together before being brought into contact with the droplets of fuel broth 23a.

In a second step 102 of the method 100, the hot spray droplets are allowed to pass down through the spray drying chamber 20 so they cool, gelate and solidify to form dried gel-bound particles. The spray drying chamber 20 is typically substantially cylindrical and vertically elongated in shape to accommodate the spray drying and gel formation processes that are conducted therein.

In a third step 103 of the method 100, the dried gel-bound particles are passed through a filtration chamber 30 to separate the dried gel-bound particles by mass. The filtration chamber may be as described above. It is typically substantially cylindrical and vertically elongated in shape to accommodate the size separation process that is conducted therein. The size separation process may be facilitated by the filtration chamber 30 having a cyclone generator 33 that is configured to swirl airborne particles within the filtration chamber.

In a fourth step 104 of the method 100, the dried gel-bound particles of a desired size range are collected as uranic nuclear fuel kernels 15. Dried-gel particles below a certain mass and any debris may be removed via the dust vent 50 formed or connected to the filtration chamber 30, the dust vent typically formed in the filtration chamber top portion 31 of the filtration chamber 30. Larger dried-gel particles are the desired uranic nuclear fuel kernels 15 manufactured by the method of the present disclosure and they float from the filtration chamber top portion 31 of the filtration chamber 30 to the filtration chamber bottom portion 32 and may be suitably removed from the filtration chamber 30, typically via a fuel kernel outlet 34 this is formed or connected to the filtration chamber bottom portion 32 of the filtration chamber 30.

The desired size range of the uranic nuclear fuel kernels 15 may be from 200 to 1000 pm in diameter.

The uranic material in the fuel broth 22a may be selected from uranium dioxide, uranium carbide, or a mixture of uranium carbide and uranium-plutonium carbide; the gelling agent in the fuel broth 22a may be sodium alginate; the hot gas 24a may be air, argon or nitrogen or a mixture thereof; and the gaseous reagent 25a may be ammonium chloride. Where an source of carbon other than uranium carbide or uranium-plutonium carbide is included in the fuel broth (22a) it may be carbon black.

In some embodiments, the fuel broth 22a comprises uranium dioxide, carbon black and sodium alginate; the hot gas 24a is air; and the gaseous reagent 25a is ammonium chloride.

FIG. 4 schematically represents a first embodiment of a system 11 for manufacturing coated uranic nuclear fuel kernels 18 of the present disclosure. This is essentially a modification of the systems depicted in FIGS.1 and 2 and described above but is configured to manufacture coated nuclear particle fuel particles that comprise uranic nuclear fuel kernels 15 that are coated with a kemel coating material, more specifically a porous graphite coating 61, e.g. silicon carbide (SiC) or zirconium carbide (ZrC). The porous graphite coating provides a shell that protects the uranic nuclear fuel kernel encapsulated within. It also provides the first of four coatings from which tristructurak isotropic (TRISO) nuclear fuel particles may be manufactured.

Unless specified otherwise, the features identified by reference numerals in FIG. 4 refer to the same or equivalent features described above in connection with the system 10 that is depicted in FIGS. 1 and 2.

The system 11 includes a coating broth inlet 27 that is formed in the spray drying chamber 20 and is configured to supply a coating broth 27a into the spray drying chamber 20 from a supply of coating broth 27b. The coating broth inlet 27 is located near the fuel broth inlet 23 so that at least a portion of the coating broth 27b is able to coat the droplets of fuel broth 23 that are supplied to the spray dry chamber 20 from the supply of fuel broth 23b.

In the embodiment shown, the fuel broth inlet 23 is integrated with the coating broth inlet 27 so as to maximise the portion of the coating broth 27b that successfully coats, e.g. typically encapsulates, the droplets of fuel broth 23 as they enter the spray dry chamber 20. More particularly, the fuel broth inlet 23 is located within the coating broth inlet 27 and the integrated arrangement of the fuel broth inlet 23 and the coating broth inlet 27 is located at a substantially central position on the spray drying chamber top 21a to maximise the volume over which the coated droplets of fuel broth 23a are sprayed into the spray drying chamber 20.

As the coated droplets of fuel broth 23a fall within the spray drying chamber 20, they cool, gelate and solidify to form dried gel-bound particles. The direction of droplet flow and the progress of the transformation is indicated by the arrow 28. The dry gel-bound particles typically have an average diameter of 200 to 800 pm.

The system is configured to be able to supply the fuel broth 23a and the coating broth 27a into the spray drying chamber 20 and to form the coated droplets of fuel broth 23a on a static, dynamic or continuous basis. The supply may be regulated by a suitable control system (not shown) that includes a controller (not shown). Sensors (not shown) may be provided to monitor various process parameters such as temperature, pressure, and particle flow, for control, production efficiency, and safety purposes.

In the system 11 the spray drying chamber 20 is provided with the hot gas 24a from a supply of hot gas 24b and the gaseous reagent 25a from a supply of gaseous reagent 25b. In the embodiment shown in FIG. 4 the hot gas 24a and the gaseous reagent 25a are mixed prior to entering the spray drying chamber 20 via the common inlet 26. In that way the common inlet 26 may be regarded as a single inlet that operates as both the hot gas inlet (24) and the gaseous reagent inlet (25).

In the embodiment shown in FIG. 4, the hot gas 24a and the gaseous reagent 25a mix as supply lines for each converge and the mixture is supplied to the common inlet 26.

In some other embodiments, the common inlet 26 may be configured so that the hot gas 24a and the gaseous reagent 25a mixture within the common inlet 26 itself.

In yet other embodiments, the hot gas 24a and the gaseous reagent 25a may enter the spray drying chamber 20 via a separate hot gas inlet 24 and a separate gaseous reagent inlet 25 (e.g. as per FIG. 1). The hot gas inlet 24 and the gaseous reagent inlet 25 may be located in any suitable location on the spray drying chamber 20, for example they may be located adjacently or they may be located on opposing sides of the spray drying chamber 20.

All options, suitably configured, can offer useful opportunities to control and optimise the mixing of the hot gas and the gaseous reagent with the coated droplets of fuel broth.

The hot gas 24a, the gaseous reagent 25a, the fuel broth 23, the spray drying chamber 20, the uranic material, the source of carbon (if any), and the gelling agent may be as described above in relation to the system 10 for manufacturing uranic nuclear fuel kernels 15.

The coating broth 27 provides the material necessary to form the porous graphite coating 61 of the coated uranic nuclear fuel particle 18. The coating broth 27 may comprise a slurry or an organosolution of precursors for the coating and alginate or a suitable alternative thereof e.g. agar-agar, carrageenan, pectin, gelatin or xanthan gum.

Differentiation between the porous graphite coating 61 and the uranic nuclear fuel kernel 15 can be optimised if the fuel broth 23 and the coating broth 27 are immiscible, at least under the operating conditions, e.g. temperature and pressure.

The alginate is commercially available, e.g. as sodium alginate from Sigma-Aldrich.

FIG. 5 schematically represents a tristructural-isotropic nuclear fuel particle 60 that has a uranic nuclear fuel kernel 15 at its core. The uranic nuclear fuel kernel 15 may be manufactured using the system depicted in FIGS. 1 and 2 and described above.

The tristructural-isotropic nuclear fuel particle 60 has four coatings that protect the uranic nuclear fuel kernel 15. The first or innermost of the four coatings is a porous graphite coating 61. This first coating encapsulates the uranic nuclear fuel kernel 15. Such a coated nuclear fuel particle 18 may be manufactured using the system depicted in FIG. 4 and described above. The second coating, which encapsulates the first coating, is a high density graphite coating 62. The third coating, which encapsulates the second coating, is a silicon carbide coating 63. The fourth and outer most coating, which encapsulates the third coating, is an outer high density graphite coating 64.

The porous graphite coating 61, the high density graphite coating 62, the silicon carbide coating 63 and the outer high density graphite coating 64 may be using any suitable technique for the purpose, e.g. chemical vapor deposition, Low Vacuum Plasma Spray (LVPS), High Velocity Oxygen Fuel coating (HVOF), air plasma spraying (APS) or electron beam physical vapor deposition (EB-PVD). In some embodiments all four coatings are applied by chemical vapor deposition.

Tristructural-isotropic nuclear fuel comprising tristructural-isotropic nuclear fuel particles 60 is structurally more resistant to neutron irradiation, corrosion, oxidation and high temperatures than traditional nuclear reactor fuels.

FIG. 6 is a flow chart of the method 200 of the present disclosure for manufacturing tristructural-isotropic (TRISO) particle nuclear fuel.

In a first step 201 of the method 200, uranic nuclear fuel kernels 15 are manufactured according to the above described method 100 i.e. that of the second aspect of the present disclosure.

In a second step 202 of the method 200, the uranic nuclear fuel kernels 15 are encapsulated with a kernel coating material, more specifically a porous graphite coating is material, to form a porous graphite coating 61; In a third step 203 of the method 200, a high density graphite coating material is subsequently applied to form a high density graphite coating 62.

In a fourth step 204 of the method 200, a silicon carbide coating material is subsequently applied to form a silicon carbide coating 63.

In a fifth step 205 of the method 200, an outer high density graphite coating material is subsequently applied to form a tristructural-isotropic (TRISO) particle nuclear fuel 60.

The porous graphite coating 61, the high density graphite coating 62, the silicon carbide coating 63 and the outer high density graphite coating 64 may be using any suitable technique for the purpose, e.g. chemical vapor deposition, Low Vacuum Plasma Spray (LVPS), High Velocity Oxygen Fuel coating (HVOF), air plasma spraying (APS) or electron beam physical vapor deposition (EB-PVD).

In some embodiments, all four coatings are applied by chemical vapor deposition. It will be apparent to the skilled person that whilst the embodiments described herein have only mentioned a single hot gas inlet and a single gaseous reagent inlet, the apparatus and method will also work in similar system utilising a plurality of hot gas inlets and a single gaseous reagent inlet, a plurality of gaseous reagent inlets and a single hot gas inlet, or a plurality of both hot gas inlets and gaseous reagent inlets.

As mentioned previously, the nature of the gaseous reagent, hot gas, and fuel broth can vary in dependence on one another, in that different combinations of gaseous reagent, hot gas, and fuel broth can be used to create different types of nuclear fuel kernel. Importantly, the advantages of large-scale production of robust, highly spherical fuel kernels in quantities suitable for mass-market consumption, can be realised with a variety of different fuel broth, hot gas, and gaseous reagent combinations using the apparatus and method described herein.

Various examples have been described, each of which comprise one or more combinations of features. It will be appreciated by those skilled in the art that, except where clearly mutually exclusive, any of the features may be employed separately or in combination with any other features and the invention extends to and includes all combinations and sub-combinations of one or more features described herein.

Claims

CLAIMS1. A system (10) for manufacturing uranic nuclear fuel kernels (15), the system comprises: a spray drying chamber (20) that has a spray drying chamber top portion (21) and s a spray drying chamber bottom portion (22); a filtration chamber (30) that has a filtration chamber top portion (31) and a filtration chamber bottom portion (32); and a feed pipe (40) that connects the spray drying chamber bottom portion (22) of the spray drying chamber and the filtration chamber top portion (31) of the filtration chamber; the spray drying chamber (20) comprising: a fuel broth inlet (23) configured to supply a fuel broth (23a) in the form of droplets from a supply of fuel broth (23b) into the spray drying chamber top portion (21) of the spray drying chamber; a hot gas inlet (24) configured to supply a hot gas (24a) from a supply of hot gas (24b) into the spray drying chamber top portion (21) of the spray drying chamber; and a gaseous reagent inlet (25) configured to supply a gaseous reagent (25a) from a supply of gaseous reagent (25b) into the spray drying chamber top portion (21) of the spray drying chamber; the fuel broth inlet (20), the hot gas inlet (30) and the gaseous reagent inlet (40) being oriented so that the droplets of fuel broth (23a) interact with the hot gas (24a) and the gaseous reagent (25a) to form gel-bound particles; and the filtration chamber (30) has a cyclone generator (33) that is configured to swirl the gel-bound particles received from the spray drying chamber bottom portion (22) of the spray drying chamber and form uranic nuclear fuel kernels (15) that are dispensable from a fuel kernel outlet (34) that is formed in the filtration chamber bottom portion (32) of the filtration chamber (30).
2. The system of claim 1, wherein the hot gas inlet (24) and the gaseous reagent inlet (25) are integrated.
3. The system of claim 1 or 2, wherein the fuel broth (23a) comprises a mixture of a uranic material and a gelling agent.
4. The system of claim 3, wherein the uranic material is uranium dioxide (UO2), uranium carbide (UCO), or a mixture of uranium carbide and uranium-plutonium carbide (UPuC).
5. The system of claim 3 or 4, wherein the fuel broth (23a) further comprises carbon black.
6. The system of any one of claims 3 to 5, wherein the gelling agent is sodium alginate.
7. The system of any preceding claim, wherein the hot gas (24a) is air, argon or nitrogen or a mixture thereof.
8. The system of any preceding claim, wherein the gaseous reagent (25a) is ammonium chloride.
9. The system of any preceding claim, wherein a dust vent (50) is formed in the filtration chamber top portion (32) of the filtration chamber (30).
10. A method (100) for manufacturing uranic nuclear fuel kernels (15), the method comprising the steps of: bringing one or more streams of a hot gas (24a) and one or more streams of a gaseous reagent (25a) into contact with droplets of a fuel broth (23a) in a spray drying chamber top portion (21) of a spray drying chamber (20) to form a spray of hot droplets, the fuel broth (23a) comprising a uranic material and a gelling agent (101); allowing the hot spray droplets to pass down through the spray drying chamber (20) so they cool, gelate and solidify to form dried gel-bound particles (102); passing the dried gel-bound particles through a filtration chamber (30) to separate the dried gel-bound particles by mass (103); and collecting the dried gel-bound particles of a desired size range as uranic nuclear fuel kernels (15) (104).
11. The method of claim 10, wherein the hot gas (24a) and the gaseous reagent (25a) are mixed together before being brought into contact with the droplets of fuel broth (23a).
12. The method of claim 10 or 11, wherein the desired size range of the uranic nuclear fuel kernels (15) is from 200 to 1000 pm in diameter.
13. The method of any one of claims 10 to 12, wherein: the uranic material in the fuel broth (22a) is selected from uranium dioxide (UO2), uranium carbide (UCO), or a mixture of uranium carbide and uranium-plutonium carbide (UPuC); the gelling agent in the fuel broth (22a) is sodium alginate; the hot gas (24a) is air, argon or nitrogen or a mixture thereof; and the gaseous reagent (25a) is ammonium chloride.
14. The method of claim 13, wherein: the fuel broth (22a) comprises uranium dioxide (UO2), carbon black and sodium alginate; the hot gas (24a) is air; and the gaseous reagent (25a) is ammonium chloride.
15. The method of any one of claims 10 to 14, wherein the droplets of a fuel broth (23a) are brought into contact with a coating broth (27a) that comprises graphite and alginate upon entering the spray drying chamber to form coated nuclear particles (18) that comprise uranic nuclear fuel kernels (15) encapsulated with a porous graphite coating (61).
16. A method (200) for manufacturing tristructural-isotropic (TRISO) particle nuclear fuel (60), the method comprising the steps of: manufacturing uranic nuclear fuel kernels (15) according to the method (10) of any one of claims 10 to 15; encapsulating the uranic nuclear fuel kernels (15) within a porous graphite coating (61); subsequently applying a high density graphite coating (62); subsequently applying a silicon carbide coating (63); and subsequently applying an outer high density graphite coating (64) to form a tristructural-isotropic (TRISO) particle nuclear fuel (60).
17. The method of claim 16 wherein the porous graphite coating (61), the high density graphite coating (62), the silicon carbide coating (63), and the outer high density graphite coating (64) are applied by chemical vapor deposition.