Decay heat and decay rate of actinides in highly neutron-irradiated uranium initially of high 235U content

The contributions from actinides to the decay heat and the decay rate relative to those from fission products in highly irradiated 235U-enriched uranium has been assessed. This assessment, which is based on measured and associated calculated actinide concentrations in a sample of uranium in which the 235U had been burned to 17% of its original >97% content (i.e., to about 17% 235U), indicates that for most practical times (<108 s) after reactor shutdown, the actinide contribution to the decay heat and to the decay rate is a reasonably small fraction (<7%) of the total and comes mainly from 237U, 238Np, and 238Pu. These results differ from those for uranium only slightly enriched in 235U