Fission Product Yields of ²³⁸U Samples Irradiated Using the Flattop Critical Assembly

Integral fission yield measurements were performed on the Flattop critical assembly at the National Criticality Experiments Research Center (NCERC) located at the Nevada National Security Site. Four DU samples, along with dosimetry foils, were positioned at two different positions within the glory hole passing through the natural uranium outer reflector and into the HEU core of the Flattop assembly. The samples were each irradiated in sets of two in separate low-power and high-power irradiations, along with a fission chamber designed especially for use in Flattop, to determine the absolute number of fissions in the samples. These measurements were designed to look at variations in the ²³⁸U fission product yields as a function of neutron energy, by having samples at different positions within the assembly and hence seeing different neutron spectra. Select fission products were isolated in duplicate from each DU target via radiochemical separations and measured for beta and gamma decay. This talk will highlight the yields measured from Sr, Mo, Zr, Cd, Ag, Cs, Ba, and Nd fission products and will compare the results to current ENDF measurements. The number of fissions measured from ⁹⁹Mo will also be compared against fission chamber counts during the low-powered run.