SPECIFIC-HEAT OF UO2-BASED SIMFUEL

The specific heats of SIMFUEL (simulated high-burnup UO2-based fuel) w ith equivalent burnups of 3 and 8 at.% were measured between room temp erature and 1400 degrees C. The results from samples annealed at three different oxygen potentials showed only small changes with burnup and oxygen potential: the specific heat increased slightly with burnup an d oxygen potential. An analytical expression describing specific heat as a function of burnup and oxygen-to-metal ratio (O/M; M represents t he uranium and the dissolved metal atoms in the fluorite matrix) is pr oposed. Changes in the shape of plots of C-p as a function of temperat ure in the form of 'humps' for hyperstoichiometric UO2+x could be rela ted to the dissolution of the U4O9 phase observed by X-ray diffraction at room temperature. The plots of C-p as a function of temperature fo r SIMFUEL, preannealed under the same conditions, did not show the hum ps, and X-ray diffraction did not show any indication of U4O9 formatio n. (C) 1997 Elsevier Science B.V.