Conversion of OPAL from U₃Si₂ to High Density U–Mo Fuel. Annex III

The ongoing development of high density low enriched uranium (LEU) fuels to replace the current application of highly enriched uranium (HEU) fuels, in accordance with the non‑proliferation and security objectives of the Global Threat Reduction Initiative (GTRI), offers an opportunity to assess the impact of such fuels on performance and reactor core parameters. The performance of the current 4.8 gU/cm³ U₃Si₂ fuel in the Open Pool Australian Lightwater (OPAL) reactor is compared against that estimated for a variety of potential U–Mo high density fuels that range in density from 6.0 to 8.0 gU/cm³. The comparison includes cycle length, fuel usage, shutdown system performance, neutron fluxes in irradiation positions, kinetic parameters and reactivity feedback coefficients.High performance research reactors depend on a compact core design to maximize the neutron flux available for irradiation and beam facilities. The most readily available technology to achieve this goal is the use of HEU fuels. The extensive experience and demonstrable reliability and performance of such fuels makes them a clear choice for most of the high performance research reactors around the world. In addition, there are gains in fuel economy through maximization of fuel burnup and minimization of parasitic neutron absorption, which is present in some of the LEU fuels. In the spirit of GTRI, new high density LEU fuels are being developed with the intention of providing a non‑proliferation option while maintaining much of the performance expected from HEU fuels. One of the most promising high density LEU fuels is a uranium–molybdenum (U–Mo) alloy dispersion type fuel in an aluminium matrix. The addition of Mo stabilizes the uranium during irradiation and several different densities of uranium and alloy compositions are considered in this study, as no qualified fuel exists at this time.The current core design is optimized for the use of 4.8 gU/cm³ U₃Si₂ fuel. This study was performed while maintaining the core and fuel dimensions (specifically the fuel meat, fuel plate and coolant channel thicknesses) and only the fuel meat composition was modified. The estimated performance parameters were calculated using the same codes and methods that were used for the U₃Si₂ calculations. In this way a direct comparison can be made to assess the impact of using high density U–Mo fuel.