Heat capacity measurements on unirradiated and irradiated fuel pellets

Heat capacities (C-p) of oxide fuels are essential for the evaluation of fu el temperature at normal, transient and accidental conditions of light wate r reactors. In this study, the effect of soluble fission products (FPs) was first examined, and then the C-p measurement technique was improved to obt ain reliable data for irradiated pellets of smaller than the standard size. A differential scanning calorimeter was applied to the C-p measurements. F rom the measurements of standard size alpha -Al2O3, the inaccuracy of the a pparatus was estimated to be about 4%. The C-p data of undoped and simulate d FPs-doped UO2 pellets of standard size were measured in the temperature r egion from 325 to 1673 K. From these results, the effect of impurities on t he C-p values of UO2 pellets and the presence of the C-p anomalies in the s imulated FPs-doped UO2 pellets were investigated. For measurements of small size specimens, the sample-side crucible was modified. The inaccuracy of t he apparatus was estimated to be 5% using a small size of the alpha -Al2O3 sample. This improved technique was applied to obtain the C, data of UO2 an d UO2-10 wt%Gd2O3 specimens with small sizes from 325 to 1673 R, which had been irradiated at isothermal conditions in a test reactor. (C) 2001 Elsevi er Science B.V. All rights reserved.