Validation of advanced in-pin metallic fuel models of SAS4A

The SAS4A safety analysis code has been extended to include mechanistic and physics-based models of U-Pu-Zr and U-Zr metallic fuel pins. The predictions of the code for various phenomena such as fission gas behavior, clad wastage formation, thermal expansion, creep, and gas swelling induced axial fuel relocation, in-pin molten fuel ejection, and clad failure models have been significantly improved. The paper presents the validation effort of the new code using the results of eight sets of TREAT MSeries overpower experiments, prior to clad failure. Fuel axial expansion reactivity and clad failure behavior was benchmarked. The results show that the code predictions are satisfactory. (authors)