A comparison between fission gas release data and FEMAXI-IV code calculations

Abstract

The FEMAXI-IV code is an extension of the earlier version FEMAXI-III. The primary improvement in the new version is the provision for treating the fuel rod behavior during an operational transient. For this purpose, the time-dependent models are used for heat conduction, fission gas release, and mixing of the released gas with the plenum gas. In FEMAXI-IV, the fission gas release model was thoroughly revised from the previous version. It is based on the fission gas release model presented by White and Tucker. The model takes into account the following mechanisms: • - diffusion of gas atoms to the grain boundary; • - sweeping of gas atoms by grain growth; • - precipitation of gas atoms into intragranular gas bubbles; • - resolution of gas atoms from intragranular and grain boundary gas bubbles; • - fission gas release due to bubble interconnection. The model was incorporated into FEMAXI-IV and code calculations were compared with the fission gas release data obtained in the Inter-Ramp and Over-Ramp experiments. This paper describes the fission gas release model involved and results of calculations.