Measured and Calculated Rates of Decay Heat in Irradiated ²³⁵U, ²³³U, 239Pu, and ²³²Th

Samples of ²³⁵U, ²³³U, ²³⁹Pu, and ²³²Th have been irradiated in high neutron fluxes [>10¹⁴ n/ (cm² sec)] and their decay heat has been measured as a function of cooling time ranging from 14 to 4500 h after removal from the high flux. To measure the rate of heat emission, an underwater calorimeter has been developed. For the measured exposure histories, decay heat has also been calculated for concentrations of 190 fission products, all significant heavy isotopes, and structural nuclides. Account is taken of the energy carried by gamma rays that escape the calorimeter. Measurements and calculations of the decay heat captured within the calorimeter agree within two standard deviations for all samples and cooling times and, in general, agree within 2%. For the ²³⁵U sample, calculations based on the Proposed ANS Standard ANS-5.1 (ANSI N18.6) agree with the measurements within a few percent.