Assessing Uncertainty in Plutonium Production Estimates Based on the Isotope Ratio Method

Abstract Independent estimates of lifetime plutonium production can be made using forensic measurements of characteristic indicator isotope ratios in core structural elements in shut-down nuclear reactors. Incomplete knowledge of a reactor’s operational history, including fuel burnup, as well as uncertainties in nuclear cross-section data, can significantly affect such plutonium estimates, making it potentially difficult to match estimates with a state’s declaration. Monte Carlo methods and sensitivity analysis techniques are used to assess the propagation of different uncertainties and their impact on plutonium estimates in infinite lattice models of a heavy-water moderated reactor (CANDU 6) and a graphite-moderated reactor (the 5 MWe reactor in North Korea), with titanium-48/titanium-49 and boron-10/boron-11 as the respective indicator isotope ratios. A tolerance interval model, with specified confidence levels, rather than one based on mean values and standard deviations, is proposed for assessing plutonium estimates based on isotope ratios measurements.