Evaluation fuel slug eccentricity effects on fuel performance

Abstract

Metallic fast reactor fuel is often formed via a casting process. This paper explores the potential role of mold casting tolerances in the formation of non-circular fuel slugs, and how such variability in shape may affect fuel swelling and the potential for excessive strain in the cladding at lower fuel burnups. The fuel performance simulation effort presented in this paper was executed using Idaho National Laboratory’s BISON fuel performance code. Three fuel configurations are included in this analysis: circular, elliptical, and maximum eccentric fuel all with the same 75% smeared density. For eccentric fuel cross sections, temperature gradients on the fuel surface along the long dimension of the oval are greater, leading to fuel anisotropic deformation due to creep. Stress emerging due to fuel-cladding contact forces fuel to creep into available cavities and creates very little cladding strain. The cladding experiences a hoop stress surge when contacted by the fuel. However, the magnitude of the hoop stress is inconsequential compared to the cladding yield stress. Thus, the dimensional variations possible for fuel slugs cast in common quartz tubing molds is not expected to impact overall fuel performance nor increase the probability of fuel cladding failure at early life.