Swelling of U-Mo Monolithic Fuel: Developing a Predictive Swelling Correlation under Research Reactor Conditions

Abstract

Understanding swelling behavior in monolithic, uranium-molybdenum, plate-type fuel is necessary to qualify the fuel for reactor use and for the conversion of high performance research reactors from highly enriched to low-enriched uranium. Multiple mechanisms influence plate dimensional stability, including solid and gaseous fission-product induced swelling, irradiation-assisted creep, fuel-phase transformation, and interaction-layer formation. Separating these phenomena remains a challenge, and current models do not appear to adequately predict experimental results at higher fission densities where it is most critical. To mitigate the mechanistic uncertainty, post-irradiation profilometry is used to increase the number of data points available over a range of in-reactor irradiation experiments conducted at the Advanced Test Reactor, and to provide a statistical precedent for a swelling-behavior model. This work establishes a predictive swelling correlation as a function of fission density, with associated confidence and prediction bounds, by analyzing more than 18,000 thickness data points collected on 74 irradiated U-10Mo monolithic fuel test plates over a range of irradiation conditions.