An Active Interrogation Technique Based on Photofission for Non-destructive Assay of Used Nuclear Fuel

Graduation date: 2016High-energy delayed γ-rays from photofission were demonstrated to be signatures for detection and identification of special nuclear materials. Such γ-rays were measured in between linac pulses using independent data acquisition systems. A list-mode system was developed to measure low-energy delayed γ-rays after irradiation. Photofission product yields of ²³⁸U and ²³⁹Pu were determined based on the measured delayed γ-ray spectra. The differential yields of delayed γ-rays were also proven to be able to discriminate nuclear and non-nuclear materials. The measurement outcomes were compared with Monte Carlo simulation results. It was demonstrated that the current available code has capabilities and limitations in the simulation of photofission process.\ud \ud A two-fold approach was used to address the high-rate challenge in used nuclear fuel assay based on photofission technique. First, a standard HPGe preamplifier was modified\ud to improve its capabilities in high-rate pulsed photofission environment. Second, advanced pulse processing algorithms including template-matching and de-randomization methods were shown to greatly improve throughput rate without large sacrifice in energy resolution at ultra-high input count rate