Density, Porosity and Grain Size, (II) Irradiated ROX Fuels to Burn-up of 28%FIMA

Abstract

The irradiation of ROX fuels to a burn-up of 28%FIMA in JRR-3M was made. Obtained results from post-irradiation examinations are: (1) The fuel bulk density of the ROX-SZR decreased by irradiation from 4.6g/cc (82%TD) to 3.4g/cc (61%TD), while that of the ROX-Th02 also decreased from 5.2g/cc (83%TD) to 3.4g/cc (55%TD). (2) The porosity of the ROX-SZR increased from 18 to 39%, while that of the ROX-Th0 2 also increased from 17 to 46%. The increase of porosity, that is, the unconstrained gas bubble swelling in the present case might be attributed to the agglomeration of pores, where Ab0 3 and PuAl 11 0 18 of ROX components took an important role. (3) The rate of unconstrained gas bubble swelling was estimated to be 0.8%LlV /V per 1%FIMA for the ROX-SZR and 1%LlV /V per 1%FIMA for the ROX-Th02, respectively. For U02, it was about 1%LlV /V per 1 %FIMA. Hence, with respect to the rate of unconstrained gas bubble swelling between the ROX fuels and U02, the difference was insignificant. (4) The average grain size of the ROX-SZR increased from 2 to 6 µm, while that of the ROX-Th0 2 increased from 2 to 4 µm. A grain growth occurred slightly.