Nuclide composition non-uniformity in used nuclear fuel for considerations in pyroprocessing safeguards

An analysis of a pyroprocessing safeguards methodology employing the Pu-to-²⁴⁴Cm ratio is presented. The analysis includes characterization of representative used nuclear fuel assemblies with respect to computed nuclide composition. The nuclide composition data computationally generated is appropriately reformatted to correspond with the material conditions after each step in the head-end stage of pyroprocessing. Uncertainty in the Pu-to-²⁴⁴Cm ratio is evaluated using the Geary-Hinkley transformation method. This is because the Pu-to-²⁴⁴Cm ratio is a Cauchy distribution since it is the ratio of two normally distributed random variables. The calculated uncertainty of the Pu-to-²⁴⁴Cm ratio is propagated through the mass flow stream in the pyroprocessing steps. Finally, the probability of Type-I error for the plutonium Material Unaccounted For (MUF) is evaluated by the hypothesis testing method as a function of the sizes of powder particles and granules, which are dominant parameters to determine the sample size. The results show the probability of Type-I error is occasionally greater than 5%. However, increasing granule sample sizes could surmount the weakness of material accounting because of the non-uniformity of nuclide composition.