Delayed Gamma-Ray Spectroscopy for Spent Nuclear Fuel Assay

High-energy, beta-delayed gamma-ray spectroscopy is investigatedas a nondestructive assay technique for the determinationof plutonium mass in spent nuclear fuel. This approach exploitsthe unique isotope-specific signatures contained in the delayedgamma-ray emission spectra detected following active interrogationwith an external neutron source. A high-fidelity modelingapproach that couples radiation transport, analytical decay/depletion, and a newly developed gamma-ray emission sourcereconstruction code is described. Initial simulations and analysiswere performed for “one-pass” delayed gamma-ray assay that focusedon the long-lived signatures. Also presented are the resultsof an independent study that investigated “pulsed mode” measurementsto capture the likely more isotope-specific, short-livedsignatures. The initial modeling results outlined in this paper suggestthat Pu-239 may be assayed in a typical 17x17 pressurizedwater reactor (PWR) assembly with a statistical uncertainty of afew percent using commercially available gamma-ray spectrometersand a neutron generator with a source strength on the orderof 1011 n/s.