Model development for uncertainty of fuel crust formation

Abstract

During severe accidents such as an anticipated transient without scram in sodium-cooled fast reactors, it is important to analyze multiphase multi-component flow behavior, when a part of disrupted core material is discharged outside the disrupted core region through control rod guide tubes (CRGTs). In particular, the fuel crust formation on a CRGT wall of the disrupted core side is an important phenomenon that affects the redistribution of disrupted fuel (the fuel discharged and the fuel remaining in the disrupted core region). Fast reactor safety analysis codes, SIMMER-III and SIMMER-IV, have been developed to evaluate the possibility of prompt criticality caused by the motion of molten core materials, and the material relocation of the disrupted core materials. This paper describes a developed model for phenomenological uncertainty of the fuel crust formation in core disruption phases in actual reactors. The model improves the applicability of the SIMMER code to the actual reactors.