Analysis of fuel rod behavior during loss-of-coolant accidents using the BISON code: Cladding modeling developments and simulation of separate-effects experiments

BISON is a finite-element based, multidimensional fuel performance code developed at Idaho National Laboratory. In this paper, we present BISON modeling developments for Zircaloy nuclear fuel cladding behavior under loss-of-coolant accident (LOCA) conditions and code validation to separate-effects experiments. Code developments include models for cladding high-temperature creep, crystallographic phase transition, high-temperature steam oxidation and failure due to burst. Code validation is performed against a substantial number of experimental tests for ballooning and burst behavior of Zircaloy claddings under LOCA conditions. Validation calculations are completed using 2D axisymmetric models. Additionally, we present a 3D calculation that demonstrates simulation of the cladding response in presence of azimuthal temperature variations. Calculated results are systematically compared to experimental data of cladding temperature, inner pressure and time at burst failure. Several of the presented BISON validation cases were developed in the framework of the IAEA Coordinated Research Project FUMAC. BISON modeling developments for UO₂ fuel behavior under LOCA conditions and code validation to integral fuel rod experiments are presented in a complementary paper.