Verification of COSMOS code using MOX TFDB of IFA-651.1

A fuel performance code, COSMOS, has been developed and consistently improved for the analysis of MOX fuel as well as UO2 fuel up to a high burnup. The main purpose of the COSMOS is to analyze the thermal behavior, rod internal pressure, and the fission gas release in the fuel rod. The thermal conductivity and fission gas release models have been developed by considering the microstructural heterogeneity in the MOX fuel due to the incomplete mixing of the PuO2 powder with the UO2 powder, Furthermore the following in-pile phenomena have been substantially updated recently: (1) pellet-cladding mechanical interaction, (2) cladding oxidation, and (3) a user-friendly graphic interface to improve the input and output system. The irradiation of IFA-651.1 was commenced in June 2000 and the latest irradiation test was performed from November 2002 to May 2003. Two MOX fuels have been loaded in IFA-651.1 with the reference MOX fuel provided by BNFL. The two MOX fuels in IFA-651.1 have been fabricated by attrition milling in cooperation of KAERI and PSI. The burnup reached more than 20MWd/kgHM and the fuel centerline temperature was ∼1000 C for the MOX fuels. The COSMOS code has been verified using the in-pile data from the MOX fuels in the IFA-651.1. The thermal conductivity and fission gas release models developed for the COSMOS were applied with the radial power distribution for the IFA-651.1 in the HBWR. The densification and swelling parameters were given by the values measured by the pressure transducer. The in pile thermal behavior was accurately simulated by the COSMOS code. The detailed comparison between the measurement and estimation for the rod internal pressure shows the qualification of the implemented fission gas release model into the COSMOS code. (Author)