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 ∼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.