ENHANCING TOUGHNESS IN MICROENCAPSULATED NUCLEAR FUEL

Abstract

Micro encapsulated fuel particles enhance safety in high-temperature gas cooled reactors by employing multiple barriers to fission product release. Microencapsulated fuel particles also have the potential to do the same in other reactor platforms. The present disclosure provides a method for enhancing the ability of microencapsulated fuel particles to retain radionuclides and thereby further enhance safety in nuclear reactors. Specifically, a nuclear fuel particle including a fuel kernel; a buffer graphitic carbon layer; an inner pyrolytic carbon layer; a multilayer pressure vessel; and an outer pyrolytic carbon layer is disclosed. The multilayer pressure vessel includes alternating layers of silicon carbide and pyrolytic carbon.

Claims

1) A nuclear fuel particle, comprising: a fuel kernel; a buffer graphitic carbon layer; an inner pyrolytic carbon layer; a multilayer pressure vessel; and an outer pyrolytic carbon layer.

2) The nuclear fuel particle according to claim 1, wherein the multilayer pressure vessel includes at least three layers in which a pyrolytic graphite layer is present between two layers of silicon carbide.

3) The nuclear fuel particle according to claim 2, wherein the multilayer pressure vessel includes at least one additional pair of pyrolytic graphite layer and silicon carbide layer between the pyrolytic graphite layer and one of the two layers of silicon carbide.

4) The nuclear fuel particle according to claim 3, wherein the pyrolytic graphite layer(s) and the silicon carbide layer(s) alternate throughout the multilayer pressure vessel, thereby the pyrolytic graphite layers separate layers of silicon carbide.

5) The nuclear fuel particle according to claim 2, wherein a thickness of the silicon carbide layers of the multilayer pressure vessel is at least 2 times a thickness of the pyrolytic graphite layers of the multilayer pressure vessel.

6) The nuclear fuel particle according to claim 1, wherein the fuel kernel includes fissile and/or fertile materials in an oxide, carbide, or oxycarbide form.

7) The nuclear fuel particle according to claim 1, wherein the fuel kernel includes low enriched uranium (LEU) of any suitable enrichment level.

8) A method for forming a nuclear fuel, comprising: providing a fuel kernel; depositing a buffer graphitic layer on the fuel kernel; depositing an inner layer of pyrolytic carbon onto the buffer graphitic layer; depositing a multilayer pressure vessel onto the inner layer of pyrolytic carbon; and depositing an outer layer of pyrolytic carbon onto the multilayer pressure vessel.

9) The method according to claim 8, wherein the multilayer pressure vessel includes at least three layers in which a pyrolytic graphite layer is present between two layers of silicon carbide.

10) The method according to claim 9, wherein the multilayer pressure vessel includes at least one additional pair of pyrolytic graphite layer and silicon carbide layer between the pyrolytic graphite layer and one of the two layers of silicon carbide.

11) The method according to claim 10, wherein the pyrolytic graphite layer(s) and the silicon carbide layer(s) alternate throughout the multilayer pressure vessel, thereby the pyrolytic graphite layers separate layers of silicon carbide.

12) The method according to claim 9, wherein a thickness of the silicon carbide layers of the multilayer pressure vessel is at least 2 times a thickness of the pyrolytic graphite layers of the multilayer pressure vessel.

13) The method according to claim 8, wherein the fuel kernel includes fissile and/or fertile materials in an oxide, carbide, or oxycarbide form.

14) The method according to claim 8, wherein the fuel kernel includes low enriched uranium (LEU) of any suitable enrichment level.

15) The method according to claim 8, wherein each of the depositing steps occurs in a fluidized chemical vapor deposition (CVD) furnace.

16) The method according to claim 15, wherein each of the depositing steps includes flowing reactant gases and optional carrier gases inside the furnace.

17) The method according to claim 16, wherein the depositing steps include the carrier gases, and the carrier gases are selected from Ar, H, or mixtures thereof.

18) The method according to claim 16, wherein the reactant gases include: acetylene (C.sub.2H.sub.2), the decomposition of which form a porous buffer carbon layer; a mixture of acetylene and propylene (C.sub.3H.sub.6), the decomposition of which form an inner pyrolytic carbon layer; and methyltrichlorosilane (CH.sub.3SiCl.sub.3 or MTS), the decomposition of which form an isotropic layer of silicon carbide.

19) A method for forming a nuclear fuel, comprising: providing a fuel kernel in a fluidized chemical vapor deposition (CVD) furnace; depositing a buffer graphitic layer on the fuel kernel by decomposition of acetylene; depositing an inner layer of pyrolytic carbon onto the buffer graphitic layer by decomposition of a mixture of acetylene and propylene; depositing a multilayer pressure vessel onto the inner layer of pyrolytic carbon by alternatingly decomposing methyltrichlorosilane (CH.sub.3SiCl.sub.3 or MTS) and a mixture of acetylene/propylene during a continuous coating layer deposition process; and depositing an outer layer of pyrolytic carbon onto the multilayer pressure vessel by decomposition of a mixture of acetylene and propylene.

20) The method according to claim 19, wherein each of the depositing steps are deposited in a serial coating run without any interruption.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which:

[0027] FIG. 1 is a schematic diagram illustrating a traditional TRISO fuel particle; and

[0028] FIG. 2 is a schematic diagram illustrating a fuel particle according to an embodiment of the invention.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0029] The following detailed description can be read in connection with the accompanying drawings in which like numerals designate like elements.

[0030] FIG. 2 is a schematic diagram illustrating a fuel particle according to an embodiment of the invention. In FIG. 2, fuel particle 20 includes a fissile fuel kernel 21, a buffer graphitic layer 22, an inner pyrolytic carbon layer 23, a multilayer pressure vessel 24, and an outer pyrolytic carbon layer 25. The multilayer pressure vessel 24 includes silicon carbides layers 241 and pyrolytic graphitic layers 242 as alternating coatings and appear as stripes in the cross-section of FIG. 2.

[0031] The fuel particle 20 can be pressed into a host graphite matrix or an impermeable silicon carbide matrix (not shown) and used in a power reactor.

[0032] In the embodiment shown in FIG. 2, the fuel particle 20 includes a fuel kernel 21 at its center. The fuel kernel may comprise fissile and/or fertile materials (e.g., uranium, plutonium, thorium, etc.) in an oxide, carbide, or oxycarbide form. In a particular embodiment, the fuel kernel 21 includes low enriched uranium (LEU) of any suitable enrichment level.

[0033] When the fuel element is used for waste mitigation and/or disposal purposes, the fuel kernel 21 may alternatively or additionally include transuranics (TRU) and/or fission products extracted or otherwise reprocessed from spent fuels.

[0034] For example, the fuel element may be used for destruction of transuranic waste generated from, for example, light water reactors or decommissioned nuclear weapons. For that purpose, the fuel element may include fuel kernels 21 formed of transuranic elements extracted from a spent fuel of a light water reactor and/or a core of a nuclear weapon. According to a particular embodiment, a fuel element formed in accordance with the described methods may be used as fuel for a light water reactor to destroy the transuranic waste while, at the same time, generating power from it.

[0035] The carbon buffer layer 22 surrounds the fuel kernel 21 and serves as a reservoir for accommodating buildup of fission gases diffusing out of the fuel kernel 21 and any mechanical deformation that the fuel kernel 21 may undergo during the fuel cycle.

[0036] The inner PyC layer 23 may be formed of relatively dense PyC and seals the carbon buffer layer 22.

[0037] The multilayer pressure vessel 24 serves as a primary fission product barrier and a pressure vessel for the fuel kernel 21, retaining gaseous and metallic fission products therein. The multilayer pressure vessel 24 also provides overall structural integrity of the fuel particle 20.

[0038] In some embodiments, the SiC in the multilayer pressure vessel 24 may be replaced or supplemented with zirconium carbide (ZrC) or any other suitable material having similar properties as those of SiC and/or ZrC.

[0039] The outer PyC layer 25 protects the multilayer pressure vessel 24 from chemical attack during operation and acts as an additional diffusion boundary to the fission products. The outer PyC layer 25 may also serve as a substrate for bonding to a surrounding ceramic matrix.

[0040] The configuration and/or composition of the fuel particle 20 are not limited to the embodiments described above. Instead, it should be understood that a fuel particle consistent with the present disclosure may include one or more additional layers, or omit one or more layers other than the multilayer pressure vessel, depending on the desired properties of the fuel particle.

[0041] Although described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departure from the scope of the invention as defined in the appended claims.