Analysis of thermal fuel behaviour under steady-state irradiation using selected cases of the IAEA CRP FUMEX

Results of the project "Comprehensive Verification of the FALCON Code for Calculation of Nuclear Fuel Temperature", relating to thermal fuel behaviour under steady-state (SST) irradiation and slow power ramps are presented. Two groups of irradiation experiments carried out in the Halden Boiling Water Reactor (HBWR) are analyzed. Improvement of the prediction capability with respect to fuel temperature under SST irradiation after the earlier calibration of the selected models is confirmed. The data from the on-line measurement of fuel temperature are interpreted in consideration of the effects of Fuel Thermal Conductivity (FTC) degradation with burnup, Fission Gas Release (FGR), reduction of FTC due to development of gaseous fuel porosity, and PelletCladding Mechanical Interaction (PCMI). Relevance of the analyzed data to current new concepts of Advanced Technology Fuel (ATF) is noted.