Determining 235U Enrichment Using a Dual-Energy Approach for Delayed Neutron Measurements

Author

Angela Lynn Lousteau, University of Tennessee, KnoxvilleFollow

Date of Award

12-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Nuclear Engineering

Major Professor

Jason P. Hayward

Committee Members

Ron Pevey, Steven Skutnik, Charles Britton

Abstract

Bulk uranium items are often measured using active neutron interrogation systems to take advantage of the relatively high penetrability of neutrons, providing the ability to quickly and accurately measure uranium masses in large, dense configurations. Active techniques employ an external neutron source to induce fission in the uranium and subsequently measure emitted prompt fission or delayed neutrons. Unfortunately, the emitted neutrons from ²³⁵U [uranium-235] and ²³⁸U [uranium-238] are, for all practical purposes, indistinguishable; therefore, commonly used systems such as the Active Well Coincidence Counter, the ²⁵²Cf [californium-252] Shuffler, and other systems based on measurement of prompt or delayed fission neutrons require many representative calibration standards and/or well-known isotopic information to interpret the results (i.e., extract an isotopic mass from the effective fissionable mass), thus limiting these techniques for safeguards applications. The primary objective of this research was to develop and demonstrate a dual-energy neutron interrogation technique using a ²⁵²Cf Shuffler measurement chamber for determination of uranium enrichment, thus eliminating the need for a (traditionally separate) gamma isotopic measurement.

This new technique exploits the change in fission rates as a function of interrogating neutron energy to independently determine the ²³⁵U and ²³⁸U content in the measurement item. Dual neutron interrogation energies were achieved by adding a deuterium- tritium (D-T) neutron generator into the measurement chamber of the Oak Ridge National Laboratory ²⁵²Cf Shuffler. Results from traditional ²⁵²Cf measurements and the new D-T measurements were then used to develop a relationship between uranium enrichment and the ratio of the two delayed neutron count rates. Parameter studies were performed to optimize the measurements for each source using a combination of modeling/simulation and experimental measurements. This dissertation presents the detailed development of this novel dual-energy neutron interrogation technique. The results are promising and with engineering refinements could be deployed for routine assay of certain types of materials.

Recommended Citation

Lousteau, Angela Lynn, "Determining 235U Enrichment Using a Dual-Energy Approach for Delayed Neutron Measurements. " PhD diss., University of Tennessee, 2017.
https://trace.tennessee.edu/utk_graddiss/4748