Alvin A. Solomon

Modeling and Measurement of Thermal Properties of Ceramic Composite Fuel for Light Water Reactors

The thermal modeling of a composite fuel consisting of continuous second phase in a ceramic (uranium oxide) matrix has been carried out with aid of detailed examination of the microstructure of the composite and the interface structure. BeO and SiC were considered as second phase dispersed in UO2 matrix by weight from 0–15% to enhance the thermal conductivity. It is found that with 10% SiC, the thermal conductivity increases from 5.8 to 9.8 W/m-K at 500 K. A finite element analysis computer program ANSYS was used to create composite fuel geometries with set boundary conditions to produce accurate thermal conductivity predictions. The results were compared to analytical calculations as previously performed with the series geometry to verify the validity of using ANSYS in producing accurate thermally enhanced nuclear fuel models. Good agreement was found between experimental measured thermal conductivity for BeO-UO2 matrix and the model predictions.

Enhanced Thermal Conductivity Oxide Fuels

the purpose of this project was to investigate the feasibility of increasing the thermal conductivity of oxide fuels by adding small fractions of a high conductivity solid phase.

Thoria-based cermet nuclear fuel : cermet fabrication and behavior estimates.

Cermet nuclear fuels have been demonstrated to have significant potential to enhance fuel performance because of low internal fuel temperatures and low stored energy. The combination of these benefits with the inherent proliferation resistance, high burnup capability, and favorable neutronic properties of the thorium fuel cycle produces intriguing options for advanced nuclear fuel cycles. This paper describes aspects of a Nuclear Energy Research Initiative (NERI) project with two primary goals: (1) evaluate the feasibility of implementing the thorium fuel cycle in existing or advanced reactors using a zirconium-matrix cermet fuel, and (2) develop enabling technologies required for the economic application of this new fuel form. Critical elements in the demonstration of this new fuel form include developing low-cost fabrication methods and characterizing the cermet properties and important performance parameters. A powder-in-tube drawing and heat treatment process is being evaluated as an alternative to hot extrusion. In this method, zirconium metal and ceramic microspheres are mixed, poured into a Zircaloy shell, and compacted into simulated fuel pins. Important processing variables being evaluated include the amount of compaction required to achieve a desired matrix density and the inter-drawing thermal treatment temperature required to achieve adequate matrix fusion and grain growth.

Thoria-based cermet nuclear fuel : neutronics fuel design and fuel cycle analysis.

Cermet nuclear fuel has been demonstrated to have significant potential to enhance fuel performance because of low internal fuel temperatures and low stored energy. The combination of these benefits with the inherent proliferation resistance, high burnup capability, and favorable neutronic properties of the thorium fuel cycle produces intriguing options for advanced nuclear fuel cycles. This paper describes aspects of a Nuclear Energy Research Initiative (NERI) project with two primary goals: (1) Evaluate the feasibility of implementing the thorium fuel cycle in existing or advanced reactors using a zirconium-matrix cermet fuel, and (2) Develop enabling technologies required for the economic application of this new fuel form. This paper will first describes the fuel thermal performance model developed for the analysis of dispersion metal matrix fuels. The model is then applied to the design and analysis of thorium/uranium/zirconium metal-matrix fuel pins for light-water reactors using neutronic simulation methods.

Zirconium matrix cermet for a mixed uranium-thorium oxide fuel in an SBWR

The thorium oxide fuel cycle has been a viable technology option since the beginning of the nuclear era. By placing (Th,U)O2 in a zirconium matrix, the resulting cermet nuclear fuel properties create a strong negative void reactivity coefficient, which is especially appealing for boiling water reactor applications. The combination of the thorium fuel cycle and zirconium matrix cermets has enabled a new core design for a simplified boiling water reactor (SBWR). Core design simulations show that an 8-yr fuel cycle is achievable using this fuel concept. Further, if burnable poisons are added to the powder fabrication mix, an essentially flat reactivity swing is created that could enable an autonomous control system. In addition to the SBWR core design, a preliminary investigation is presented for experimental fuel fabrication methods designed to simplify cermet fabrication. Spray drying and sintering were used to create mixed-oxide (Th,U)O2 powders with a nominal diameter of ~200 μ, with ~10 vol% uniformly distributed porosity and nominal grain size of 5 μ. In addition, a low-temperature cermet fabrication method was used to fabricate simulated fuel pins with a porous zirconium matrix. Results from these initial development experiments are promising for the future application of the cermet fuel, but further work is required to demonstrate their viability.