Patent Application
20240062925
The present invention relates to nuclear fuel parties including nuclear fuel cores or fuel kernels surrounded by fission product-retentive outer coatings.
Tristructural isotropic (TRISO) coated particle fuel is a robust fuel form developed for high temperature gas-fueled reactors (HTGRs). TRISO fuels are also under consideration for advanced reactor fuel forms such as Fluoride-salt Cooled Reactors (FHRs) and microreactors. The TRISO particle itself is a composite. For HTGRs, the particular architecture traditionally consists a uranium oxide (UO2) kernel or a multiphase UO2 and uranium carbide kernel surrounded by successive isotropic layers. The isotropic layers, in order, include a porous buffer layer, a dense inner pyrolytic carbon layer, a silicon carbide (SiC) layer, and a dense outer pyrolytic carbon layer. The isotropic layers are deposited, uninterrupted, using fluidized bed chemical vapor deposition. Individual particles are then integrated into a final fuel form by overcoating with a graphitic matrix and compacting either into a right cylinder compact for prismatic core reactors or a spherical fuel element for pebble bed reactors.
Each isotropic layer provides specific functionality during fuel processing and operation. For example, the kernel provides fissile and fissionable material and retains fission products. The buffer attenuations fission product recoils, provides a plenum to accommodate fission gases, and accommodates kernel swelling. The inner pyrolytic carbon layer provides a gas-tight barrier to mitigate fission gas release and protects the kernel during SiC deposition. The SiC layer is a primary load bearing member and provides a barrier to the release of fission gases and metallic fission products not retained in the kernel during operation. Lastly, the outer pyrolytic carbon layer is a final gas-tight layer and provides a surface for overcoating.
Palladium and silver are of particular interest to TRISO fuel operation since they do not readily form stable oxides or carbides and are therefore readily released from the kernel and are free to interact with the SiC layer. However, the SiC layer is susceptible to corrosion by palladium and the penetration of palladium into the SiC layer. Corrosion of the SiC layer by palladium can occur locally around the circumferences of the interface between the SiC layer and the inner pyrolytic carbon layer. This local corrosion reduces the effectiveness of the SiC layer, and local disruptions in the SiC layer can lead to weakened SiC and increases its failure probability.
Accordingly, there remains a continued need for a system that limits the interaction of palladium SiC to thereby reduce TRISO failures and expand practical operating conditions.
A TRISO architecture including an improved buffer layer is provided. The improved buffer layer contains sacrificial silicon in low density carbon to react with palladium released from the kernel and thereby limit the palladium available to react with the existing SiC layer. The introduction of silicon in the buffer layer, or generally internal to the inner pyrolytic carbon layer, allows for longer fuel lifetimes and/or higher operating temperatures. Higher achievable burnups and operational temperatures can reduce fuel costs and achieve higher efficient power production. In addition, the buffer layer with silicon mitigates fuel failure from palladium corrosion, thereby increasing the safety of the TRISO fuel particle.
In one embodiment, a method for manufacturing a TRISO fuel particle includes the addition of silane or methylsilane gas during fluidized bed chemical vapor deposition in a carrier gas, for example argon gas, to form the buffer layer. The total silicon concentration in the buffer layer can vary depending on the burnup target and other performance goals such as ultimate temperature. The co-deposition of a homogenous carbon and silicon buffer layer does not add significant cost during fabrication and realizes a marked increase in fuel performance and safety. The TRISO fuel architecture of the present invention is well suited for Generation IV commercial reactors such as HTGRs and FHRs. The need for longer burnups for remote power generation or space power generation, where refueling is limited or not possible, makes the TRISO fuel architecture of the present invention an attractive option for micro-reactor designs.
These and other features and advantages of the present invention will become apparent from the following description of the invention, when viewed in accordance with the accompanying drawings and appended claims.
The present invention relates to a TRISO fuel particle and a method of manufacture. The TRISO fuel particle includes an improved buffer layer containing sacrificial silicon in low density carbon to react with palladium released from the kernel and thereby limit the palladium, and potentially silver, available to react with the silicon carbide layer. The TRISO fuel particle in accordance with one embodiment is discussed below, followed by a discussion of its method of manufacture. A working example follows, which is intended to be non-limiting.
Referring first to
The buffer layer 14 includes sacrificial silicon in low density carbon to react with palladium, prior to the palladium interacting with the silicon carbide layer 18, and thereby limiting the potential for silicon carbide corrosion. Secondarily, palladium silicides are believed to be a getter of silver. Silver released from the fuel kernel 12 forms a eutectic with silicon and may be soluble in silicon-bearing phases, thus limiting the mobile silver inventory at the silicon carbide layer 18. The buffer layer 14 defines a thickness of between 10 microns and 150 microns, inclusive, further optionally 10 microns to 20 microns inclusive, and defines a density of between 0.5 gm/cm3 and 1.5 g/cm3, inclusive (as used herein, “inclusive” means the upper and lower bounds are included in the stated range).
The inner pyrolytic carbon layer 16 protects the silicon carbon layer 18 by limiting the interaction between the silicon carbide layer 18 and the fuel kernel 12. The inner pyrolytic carbon layer 16 provides structural support to the silicon carbide layer 18 and serves as a diffusion barrier, preventing the release of fission products. The inner pyrolytic carbon layer 16 can have a thickness from 5 microns to 200 microns, inclusive, by non-limiting example, further optionally 5 microns to 10 microns, inclusive. This layer is optionally deposited from a mixture of acetylene and an inert gas, such as argon or helium, in a fluidized bed at an elevated temperature, for example 900° C. to 1800° C.
The silicon carbide layer 18 provides a robust physical barrier, with high thermal conductivity, to confine the fission products and prevent the release of radioactive materials. The silicon carbide layer 18 can include a thickness from 10 microns to 200 microns, inclusive, further optionally from 10 microns to 20 microns, inclusive. The silicon carbide layer 18 is functionally a containment shell to contain gaseous and metallic fission products. The thickness of the silicon carbide layer 18 is generally selected to withstand stress from the fission gases as they accumulate with the burning of the fuel kernel 12 as part of a high burn-up fuel cycle, thereby ensuring fission gases do not enter the coolant loop of a nuclear reactor.
The outer pyrolytic carbon layer 20 surrounds the silicon carbide layer 18 and provides a final barrier against the release of fission products. The outer pyrolytic carbon layer 20 can have a thickness from about 5 microns to about 200 microns, inclusive. This layer is optionally deposited from a mixture of acetylene and an inert gas, such as argon or helium, in a fluidized bed at an elevated temperature, for example 900° C. to 1800° C., by non-limiting example.
In another embodiment, a method of manufacture is provided. With reference to the flow chart of
After the buffer layer is formed, a carbon precursor gas, such as methane (CH4) or acetylene (C2H2), and an inert gas, such as argon or helium, is introduced into the fluidized bed chemical vapor deposition chamber at step 34. The chamber is heated to high temperatures, for example 900° C. to 1800° C., by non-limiting example. At these elevated temperatures, the carbon precursor dissociates and releases carbon atoms, which deposit onto the surface of the buffer layer until a desired thickness and uniformity is achieved. At step 36, the silicon carbide layer is formed on the inner pyrolytic layer. This step includes introducing a suitable precursor gas into the fluidized bed chemical vapor deposition chamber. The precursor gas can include a halogen precursor, such as MTS. The deposition chamber is then heated at elevated temperatures, for example up to 1800° C., causing the precursor gas to decompose. The released silicon and carbon atoms react with each other, forming a silicon carbide deposition on the surface of the inner pyrolytic layer. The resulting silicon carbide layer provides mechanical strength, a diffusion barrier, and appropriate thermal conductivity.
At step 38, the outer pyrolytic layer is formed. This step includes introducing a carbon precursor gas, such as methane (CH4) or acetylene (C2H2), and an inert gas, such as argon or helium, into the fluidized bed chemical vapor deposition chamber. The chamber is heated to elevated temperatures, for example 900° C. to 1800° C., by non-limiting example. At these elevated temperatures, the carbon precursor dissociates and releases carbon atoms, which deposit onto the surface of the silicon carbide layer until a desired thickness and uniformity is achieved. This outer layer is a final gas-tight layer and provides a surface for overcoating, if desired.
The following working example is provided for clarity and is intended to be non-limiting. A buffer coating having sacrificial silicon was directly deposited onto zirconium dioxide (ZrO2) kernels, which were a surrogate for uranium-bearing fuel kernels. The particles were fluidized within argon and coating gases of acetylene and silane were introduced to facilitate deposition of the buffer layer.
Optical imaging and scanning electron microscopy was conducted to explore the morphology and silicon distribution.
The foregoing example illustrates that co-deposited buffer layers can maintain similar properties, and most showed a uniform distribution of silicon. The presence of silicon in the buffer layer is available to interact with palladium, and possibly silver, released from the fuel kernel, mitigating deleterious palladium and silicon carbide interactions and fission product release. This co-deposition approach demonstrates the ability to deposit standalone silicon-bearing layers on a kernel without the introduction of harmful reaction byproducts, for example HCl, while increasing the operational envelope of traditional TRISO fuel architectures.
The above description is that of current embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. Any reference to elements in the singular, for example, using the articles “a,” “an,” “the,” or “said,” is not to be construed as limiting the element to the singular.
This application claims the benefit of U.S. Provisional Application 63/399,266, filed Aug. 19, 2022, and U.S. Provisional Application 63/406,318, filed Sep. 14, 2022, the disclosures of which are hereby incorporated by reference in their entirety.
This invention was made with government support under Contract No. DE-AC05-000R22725 awarded by the U.S. Department of Energy. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63399266 | Aug 2022 | US | |
| 63406318 | Sep 2022 | US |
