Evaluation of nuclear material accountability by the probability of detection for loss of Pu (LOPu) scenarios in pyroprocessing

摘要

A new methodology to analyze the nuclear material accountability for pyroprocessing system is developed. The Pu-to-244Cm ratio quantification is one of the methods for Pu accountancy in pyroprocessing. However, an uncertainty in the Pu-to-244Cm ratio due to the non-uniform composition in used fuel assemblies can affect the accountancy of Pu. A random variable, LOPu, is developed to analyze the probability of detection for Pu diversion of hypothetical scenarios at a pyroprocessing facility considering the uncertainty in Pu-to-244Cm ratio estimation. The analysis is carried out by the hypothesis testing and the event tree method. The probability of detection for diversion of 8?kg Pu is found to be less than 95% if a large size granule consisting of small size particles gets sampled for measurements. To increase the probability of detection more than 95%, first, a new Material Balance Area (MBA) structure consisting of more number of Key Measurement Points (KMPs) is designed. This multiple KMP-measurement for the MBA shows the probability of detection for 8?kg Pu diversion is greater than 96%. Increasing the granule sample number from one to ten also shows the probability of detection is greater than 95% in the most ranges for granule and powder sizes.