Analysis of fission products release under DLOFC scenario at different power levels of Indonesian PeLUIt reactor design

Abstract

Understanding fission product release is essential for ensuring reactor safety during normal operation and accident conditions. This computational study focuses on the fission product release behavior in PeLUIt reactor design under normal and Depressurized Loss of Forced Cooling (DLOFC) scenarios at different power levels, from 10 MWt to 40 MWt. It deployed STACY, a fission product release code, with input fed by TRIAC-BATAN, which evaluates the failure fraction of TRISO-coated fuel particles. Neutronic calculations were conducted using PEBBED and OpenMC while fuel irradiation temperatures and accident conditions were analyzed through a combination of PEBBED and THERMIX-KONVEX. The results indicate that the failure fraction of TRISO particles remains negligible up to approximately 2,700 h of irradiation but increases significantly at higher power due to prolonged exposure with elevated temperatures. The fractional release of some fission products were studied. I-131 exhibits the highest release fluctuations with a rapid initial release followed by stabilization. Cs-137 maintains a stable release profile which increase gradually. Ag-110 m shows the highest cumulative release among metal fission products. Sr-90 is the most retentable one in the fuel, with minimal release observed even at high power. The study confirms that a higher reactor power level effect fission product release positively due to thermal degradation of the TRISO coated fuel particle. At 10 MWt to 30 MWt, the defect fraction increase is minor, but at 40 MWt, it becomes significant due to higher temperatures and fission gas pressure; however, at 30 MWt, fission product release remains within safe limits.