Dissertation Defense: Active Interrogation of Fresh Nuclear Fuel in Shipping Containers

Sarah Sarnoski, Ph.D. candidate in nuclear engineering, will be the speaker.

Sarah Sarnoski, Ph.D. candidate in nuclear engineering, will be the speaker. Dr. Kenan Ünlü is chair of her committee.

Abstract

Currently available techniques are intrusive, requiring removal of fuel assemblies from shipping containers to assay them. It is a goal of the International Atomic Energy Agency (IAEA) to have a technique to assay assemblies without removal from shipping containers. A new technique for the assay of fresh nuclear fuel in shipping containers has been developed and benchmarking experiments performed to validate the method. The technique utilizes a tuned energy spectrum neutron source to preferentially fission U-235 and high purity germanium (HPGe) spectrometry to quantify short-lived fission products resulting from the fission process, selecting fission products that provide the greatest differentiation between U-235 and U-238 fission.

An experiment was designed to validate the proposed technique by interrogating bare fuel assemblies of Low Enriched Uranium (LEU), Depleted Uranium (DU), and a challenge assembly comprised of an unknown combination of LEU and DU fuel rods. Seventeen unique fission product gamma rays were identified in the LEU fuel. Isotope ratios were calculated for each fuel type and a χ² analysis used to determine the statistical differences between the fuel types. In a blind analysis, the composition of the challenge fuel assembly was postulated to be LEU around the perimeter with DU rods in the center of the assembly, which was revealed to be the true configuration.

Monte Carlo N-Particle (MNCP) was used to predict the measured gamma-ray spectrum and the model benchmarked with the experimental data. The simulation was then extended to model a fresh fuel assembly inside a shipping container on a semi-trailer. The results indicate that the fission product gamma rays used in the analysis of the experimental data are expected to be distinguishable above backgrounds, indicating that the proposed technique can be used to measure induced short-lived fission products through a shipping container and verify a fresh nuclear fuel assembly.