Reassessment of FRAPTRAN’s Cladding Failure Criteria in LOCA Within R2CA H2020 Project

In this study, various cladding deformation models and burst criteria were implemented in U.S. NRC’s transient fuel performance code FRAPTRAN to examine the effect on the prediction of cladding burst under loss-of-coolant accidents (LOCAs). The work is carried out within EU H2020 R2CA project (Reduction of Radiological Consequences of design basis and design extension Accidents) with the aim to improve the modelling of radiological consequences in LOCA and steam generator tube rupture (SGTR) accidents. Cladding plastic deformation in FRAPTRAN’s ballooning model BALON2 was modified by employing two high-temperature creep laws [1, 2] in combination with a dynamic crystallographic phase transformation model [3]. Additionally, new LOCA burst criteria based on true stress limit [4] developed by IRSN were tested to recalculate FRAPTRAN validation cases. The modified code modules were further incorporated in VTT’s statistical method for full core analysis to evaluate the number of failing rods in LOCA simulations of EPR type plant. The results demonstrate that the prediction of burst could be improved depending on the selected deformation model and burst criterion. Overall, the cladding creep was found to have more impact on the results than the burst criterion.