Development of Monte Carlo models of a gamma-ray nondestructive assay system for nuclear material control and accountability

Nuclear material control and accountability (NMCA) is vital to safeguarding special nuclear materials (SNM) against theft and diversion. Nondestructive assay (NDA) via gamma-ray spectrometry is one of the most common methods employed by NMCA programs to determine the amount or composition of SNM. However, accurate gamma-ray NDA of SNM can be difficult in certain scenarios due to the complex distributions and compositions samples can exhibit. Monte Carlo models of a high-purity germanium (HPGe) gamma-ray detector used for assaying plutonium were developed and benchmarked to simulate two difficult measurement scenarios often faced at Los Alamos National Laboratory (LANL): electrorefining salt (ER) residues and holdup in gloveboxes. For holdup measurements, accuracy is inherently limited because the exact distribution of material is unknown, which can lead to high uncertainties in reported masses. While the uncertainty in holdup measurements is assumed to be substantial, a thorough investigation of what an adequate value for gloveboxes at LANL should be has not been completed. Thus, measurements were simulated with various distributions of plutonium within a glovebox, and the resulting spectra were analyzed to see how the spatial distribution of material affected the measured mass. In doing so, a more accurate uncertainty value was determined. For the ER salts, NDA is hindered by samples’ complex compositions which arise from the fresh separation of elemental components and the possible presence of heterogeneities. Gamma-ray measurements of both homogenous and heterogenous samples were modelled with varying amounts of plutonium present. The simulation results from these Monte Carlo models were then used to determine the minimum detectable amount (MDA) of ²³⁵U for different plutonium masses and to develop an improved parameter set used for determining the isotopic compositions of the salts.

Author dc:creator

• McKay, Kevin Marsile

Contributors dc:contributor

• Charlton, William S.
• Landsberger, Sheldon
• John Smeltz
• Elena Zannoni
• Ryan Winkler

• Electrorefining
• FRAM
• Holdup
• MDA
• Plutonium
• MCNP
• Spectrometry
• NMCA
• NDA

Language dc:language

English

Identifier

https://doi.org/10.26153/tsw/63027

OAI identifier oai:identifier

oai:tdl-ir.tdl.org:2152/135709