Delayed Gamma Assay for Spent Nuclear Fuel Safeguards

The delayed gamma assay technique is being investigated as part of the U.S. DOE Next Generation Safeguards Initiative (NGSI) with a focus on non-destructive quantification of plutonium in spent nuclear fuel, and prompt detection of nuclear material diversion. High-energy beta-delayed gammaray signatures induced during neutron interrogation offer the capability to determine total fissile content and individual fissile and fertile isotope inventories. The objective of the research is to assess whether the delayed gamma assay instrument can provide sufficient sensitivity, isotope specificity and accuracy as required in nuclear material safeguards. A conceptual design of the delayed gamma spent nuclear assay instrument is presented, along with modeling results for several assemblies from the NGSI spent nuclear fuel libraries with a range of burnup, initial enrichment and cooling times. Variations and limitations of the assay parameters and a response analysis approach are discussed.