High-Burnup BWR LOCA Burst Analysis Framework Development

Regulatory changes for increased enrichment require better understanding of high-burnup fuel performance and relevant phenomena during a postulated loss of coolant. The Nuclear Energy Advanced Modeling and Simulation program has developed a multiphysics framework to predict fuel fragmentation, relocation, and dispersal susceptibility in nuclear fuel rods during a postulated large-break loss-of-coolant accident (LBLOCA). The framework has previously only been applied to pressurized water reactors. The industry feedback identified that a similar framework is needed for Boiling Water Reactors (BWRs). This paper describes efforts to apply the framework to a BWR. First, the Virtual Environment for Reactor Applications (VERA) was used to simulate three cycles of steady-state reactor conditions. VERA predictions were ported to steady-state fuel performance and thermal hydraulics simulations in the BISON and TRACE codes, respectively. Steady-state results from all three codes were analyzed and compared with one another to verify accuracy. Then, a postulated LBLOCA was simulated in TRACE, and the results were appended to the BISON simulations to create rod-specific fuel performance simulations of multicycle irradiation histories followed by an LBLOCA. Four rods were modeled in TRACE and BISON, including (1) a rod from a high-burnup test assembly, (2) a highest-powered fresh rod, (3) a once-burned rod, and (4) a twice-burned rod. Two cladding rupture models were implemented in the BISON simulations, but neither model predicted cladding failure in any of the rods. This is a promising initial result, but more work is needed to expand the number of rods analyzed in TRACE and BISON to create a statistically representative sample of the core.