Benchmarking and characterization of the RPI LSDS for spent fuel assay

Abstract

The Department of Energy’s MPACT Campaign funded a collaborative initiative in order to demonstrate the feasibility of Lead Slowing-Down Spectroscopy (LSDS) for the assay of individual fissile isotopes—i.e. ²³⁵U, ²³⁹Pu, and ²⁴¹Pu—in spent nuclear fuel (SNF) assemblies. Such a development would be valuable for nuclear safeguards operations, including the transportation, storage, and reprocessing of SNF. Previous experiments with the RPI LSDS involved the investigation of fresh uranium fuel samples containing ²³³U and ²³⁵U. The contribution of the research presented here is the experimental demonstration of the sensitivity of the LSDS assay method to incremental quantities of fissile U and Pu. These measurements utilize a fresh nuclear fuel pin and distinct ²³⁵U and ²³⁹Pu samples in order to better mimic the composition of SNF. The experimental data analysis algorithms were developed at PNNL, which were used to quantify the individual isotopic fissile masses of ²³⁵U and ²³⁹Pu. A linear empirical algorithm—applied to seven fissile configurations with a total ²³⁵U and ²³⁹Pu mass up to 37.4g and 138g, respectively—performed best and resulted in a root-mean-square error of 2.7% for ²³⁵U and 6.3% for ²³⁹Pu mass determination. Additional work is necessary to demonstrate a proof of principle for the isotopic assay of SNF assemblies using LSDS, but the experimental results present here demonstrate progress towards that goal.