Book Description

Fission gas release data are presented for five fuel rods irradiated at low fuel temperature (below 2700/sup 0/F) with burnups up to 90,000 MWD/MTM. Four of these rods contained ThO/sub 2/-UO/sub 2/ (33.6 weight percent UO/sub 2/) fuel pellets; the fifth rod contained ThO/sub 2/ pellets. These data supplement fission gas release information previously reported for 54 rods containing ThO/sub 2/-UO/sub 2/ and ThO/sub 2/ fuel, some of which experienced fuel temperaures up to 5000/sup 0/F and burnups to 56,000 MWD/MTM. These new data suggest that at burnups exceeding about 80,000 MWD/MTM a sharp increase in fission gas release occurs, possibly caused by microstructural changes in the fuel. This is similar to the behavior of UO/sub 2/ except that the increase occurs in UO/sub 2/ at lower burnup (approximately 40,000 MWD/MTM). The fission gas release calculational model previously reported has been modified to account for the observed increase in the low temperature component. The revised model provides a good best estimate of all the fission gas release data.