Fuel Swelling and Creep Analysis for a MURR LEU U-10Mo Monolithic Plate

Abstract

U-10Mo monolithic fuel is considered for the conversion of the US High Performance Research and Test Reactors (USHPRR) from high enriched uranium (HEU) to high density low enrichment uranium (LEU) fuel. The monolithic fuel plates are comprised of high density LEU-10Mo fuel core sandwiched between zirconium diffusion barrier interlayers and encapsulated in an aluminum alloy cladding. The conversion of the University of Missouri Research Reactor (MURR), one of the USHPRR fleet, from the use of HEU to LEU is currently in progress. Preliminary safety analysis for the conversion of MURR assumes maximum increase in plate thickness of about 0.1 mm due to irradiation effects. Finite element analysis (FEA) was used to model the thermo-mechanical behavior of a MURR LEU-10Mo monolithic plate under typical irradiation conditions in the LEU core. The maximum increase of the plate thickness was determined considering various combinations of swelling correlations and coefficient of creep rate. Analysis of the displacement profiles showed that maximum displacement along the plate thickness direction occurs at the same location in all cases. For any of the swelling correlations considered in this work, the lowest creep rate coefficient, 5 (× 10−25 cm3/MPa-fission), was found to cause larger outboard displacement. The maximum increase in plate thickness was found not to exceed 0.083 mm with a combination of fuel creep coefficient in the range between 750 and 250 (× 10−25 cm3/MPa-fission) and the the 95% UCL of the most conservative U-10Mo correlation available to describe fuel swelling.