Manufacturability of U₃Si₂ and its high temperature oxidation behaviour

High density fuels, such as uranium silicide (U₃Si₂), are being considered alongside improved cladding materials to develop new fuels which are both economic to manufacture and demonstrate enhanced accident tolerance. Through a collaborative programme led by Westinghouse and involving national laboratories in the US and UK, efforts are being made to establish a viable route by which U₃Si₂ can be manufactured and to test its suitability as a fuel. In the UK work has focused on routes to convert UF₆ and UF₄ to U₃Si₂ directly, without needing to reduce the uranium to its metallic state. Experimental observations of reactions between UF₄ and Si indicate the formation of a USi_2-x phase at a temperature of 1000 C. degrees, consistent with thermodynamic assessments. Work on the construction of a rig which will pass UF₆ heated to 1000 C. degrees through a bed of finely divided Si powder, is also reported. At Westinghouse, U₃Si₂ fabricated by the arc-melting process has been subjected to high temperature steam and synthetic air tests and the reaction rate measured as a function of temperature using differential scanning calorimetry. The rates are compared to UO₂ and UN (Uranium mononitride). At Idaho National Laboratory irradiation testing of U₃Si₂ fuel is in progress. Fuel specimens were prepared by conventional arc melting process to formulate the U₃Si₂ followed by conventional powder metallurgy processes to create pellets. These irradiation tests are intended to help resolve questions concerning the swelling of U₃Si₂ under conditions representative of LWR fuel. (authors)