PNNL

Abstract

Radioactive xenon isotopes (133Xe and 135Xe) generated by the spontaneous fission of 240Pu are useful in identifying buried transuranic waste. The generation rate of these xenon isotopes depends on the amount of 240Pu present and the cumulative fission yield (fission fraction) for each isotope. Published measurements of the cumulative yields for masses 133 and 135 were not consistent with one another. The uncertainties obtained from the variation in the literature are on the order of 13% and 10% for masses 133 and 135, respectively. The cumulative fission yields of 133Xe and 135Xe from 240Pu spontaneous fission are measured through repeated gas sampling with the goal of reducing the uncertainty in these quantities below 5%. Twenty-four gas samples were collected and analyzed for 133Xe, and 29 samples were collected and analyzed for 135Xe. The final cumulative fission yields are (6.6 ± 0.2)% for 133Xe and (5.8 ± 0.2)% for 135Xe. The uncertainties represent 3% of the final quantities. This achieves the goal of reducing the uncertainty in the measured fission yields below 5% of the total.