Development and testing of the FAST fuel performance code: Normal operating conditions (Part 1)

The Fuel And Sheath modeling Tool (FAST) is a general purpose nuclear fuel performance code. FAST includes models for heat generation and transport, thermal expansion, elastic strain, densification, fission product swelling, cracked pellet, contact, grain growth, fission gas release, gas and coolant pressure and sheath creep. The equations are solved on a two-dimensional (radial-axial) geometry of a fuel pellet and sheath using the Comsol Multiphysics finite-element platform. This paper presents the FAST code for normal operating conditions and results of the proof-of-concept testing against the ELESIM and ELESTRES-IST fuel codes as well as experimental data from seven irradiated fuel elements. In these seven cases, all of the codes were found to under-predict the measured average sheath strains. However, the FAST code was found to under-predict the mid-pellet sheath strains by a smaller margin than the other two codes. A larger data set is required to assess relative accuracy of the codes.