Year
2019
Abstract
Assessment of FRAM Measurement UncertaintiesJung H. Rim, Donivan R. Porterfield, and Michael D. YohoLos Alamos National Laboratory, Los Alamos, New Mexico, 87544, jrim@lanl.gov</i>The Fixed-Energy Response-Function Analysis with Multiple Efficiency (FRAM) code was developed at Los Alamos National Laboratory (LANL) to analyze gamma-ray spectra to determine isotopic composition of plutonium or uranium. FRAM provides the means to easily process High Purity Germanium (HPGe) gamma-ray spectra to obtain isotopic composition information. FRAM also provides concentrations of select decay progeny isotopes in the sample. FRAM is widely used in laboratory settings and globally for international safeguards applications. One of the observations made by LANL researchers using FRAM was an insufficient uncertainty estimate of the isotopic composition measurements. The isotopic composition values for Pu and U were, in some instances, not statistically consistent with the measurements performed using Thermal Ionization Mass Spectrometry (TIMS) method, the gold standard in isotopic measurements. In a review of the FRAM code, it was determined that the code does not account for nuclear data uncertainties such as gamma emission probabilities, half-lives, and atomic weights in its uncertainty calculations. For Pu and U samples, gamma emission probabilities uncertainties can be a large contributor to the expanded uncertainty and must be accounted for. To mitigate the uncertainty issues in FRAM code, a method to perform uncertainty calculations outside of the code was developed. FRAM output reports provide a great deal of spectral analysis information. GUM compliant uncertainty calculations were performed using information extracted from FRAM output reports and results were compared to the code generated measurement uncertainties. The uncertainty calculations were performed using GUM Workbench from Metrodata GmbH. This document had been reviewed and assigned publication number: 'LA-UR-19-21316'