Analyses for the Production and Dosimetry of Adding Uranium-232 as a Tracer to the Uranium Fuel Cycle

This dissertation is an examination of the use of uranium-232 as a tracer in nuclear fuel. Decay daughters from ²³²U, particularly thallium-208, produce high energy gamma rays that, when added to uranium, may increase detectability in case of theft or diversion, but are also hazardous in high quantities. Previous studies of the ²³²U decay chain are examined. This work will go in to a dosimetry study to determine how hazardous varying levels of ²³²U are, and how to efficiently produce ²³²U in sufficient quantities.

A dosimetry study was performed to determine the dose hazards due to the addition of ²³²U to uranium. This dosimetry study determined that the concentration of ²³²U to add to uranium is between 100 parts per trillion. A production scoping study was performed to determine the preferred target materials for producing ²³²U via neutron irradiations. Calculations performed using SCALE 6.2 ORIGEN determined that ²³¹Pa and ²³⁰Th are the optimum target materials, and that reactor irradiations are preferred. ORIGEN Calculations using flux spectra from the High Flux Isotope Reactor determined that ²³¹Pa calculations that the optimum irradiation time is 2 HFIR cycles, yielding 0.35 grams of ²³²U per gram ²³¹Pa. Thorium-230 irradiations yielded 0.15 grams ²³²U per gram ²³⁰Th after five cycles. Neutronics analyses examined the neutron spectra in targets modeled in MCNP, and determined that self-shielding is a concern that may reduce yield, especially in ²³⁰Th, lowering the yield to 0.1 grams after five cycles.

A study of ²³⁸Pu contaminated with ²³⁶Pu produced at the Advanced Test Reactor was also conducted base on work from the CSNR. This examined strategies for mitigating against ²³⁶Pu contamination by chemical removal of ²³²U. Only material irradiated close to the center of the ATR needed this extra processing, and only a few micrograms of ²³²U is recoverable. However, these small quantities may still have a use for small stockpiles or testing purposes.