Proliferation Resistance of Utilizing Enriched Reprocessed Uranium

Abstract:

The proliferation resistance (PR) of enriched reprocessed uranium (ERU) was investigated. The inherent intrinsic proliferation resistance to production of a uranium or plutonium based nuclear explosive device (NED) is the focus of this study. This study is expected to encourage the employment of closed nuclear fuel cycle employing light water reactors (LWRs), in order to efficiently use uranium resources and reduce the deep geological repository as well. Reprocessed uranium (RepU), compared to natural uranium contains higher concentration of ²³⁴U and other uranium isotopes, such as ²³²U, ²³³U, and ²³²U. The presence of minor isotopes affects the uranium enrichment process and in turn the composition of used fuel discharged from a power reactor. As reprocessing recycling of discharged uranium is repeated, the minor uranium isotopes tend to accumulate more in ERU. ²³⁸Pu renders plutonium less attractive for a NED and its buildup is enhanced by the increase of ²³⁶U. When ERU is used as fuel in an LWR, ²³⁸Pu content in plutonium can easily exceed 6.2% and is expected to provide high intrinsic PR, because it is an undesired isotope of plutonium in a NED due to its high decay heat and spontaneous fission rate. Besides denaturing plutonium with ²³⁸PPu, RepU holds advantage over natural uranium in terms of discouraging production of highly enriched uranium (HEU). Uranium enrichment process is to preferentially enrich ²³⁵U using a physical enrichment method and a gas centrifuge enrichment plant is a commercial means to enrich uranium in bulk. However, the presence of minor uranium isotopes ²³²U, ²³⁴U, and ²³⁶U in the discharged fuel complicates this selective ²³⁵U enrichment process. ²³²U complicates the enriched uranium product and the enrichment facility with high γ-radiation, whereas ²³⁴U and 236U are neutron poisons. A matched-abundance ratio cascade (MARC) model was applied to accurately estimate the enrichment of the multi-isotope uranium. The MARC was followed by Monte Carlo N-Particle Transport (MCNP) to simulate the burnup of ERU fuel in a conventional LWR. Both codes were successful in verifying the PR of ERU. After 3 fuel cycles, whereby discharged uranium was reprocessed, enriched, and recycled twice, denatured plutonium was attained and after the 4th fuel cycle, denatured uranium was also attained. Nevertheless, ERU became contaminated with ²³²U and ²³⁴U and the maximum burnup or the amount of electricity generation diminished after 3 fuel cycles. Therefore, further uranium recycling was impractical past that point. The potential of applying RepU regeneration technique was raised. While this technique can prolong the uranium recycling period, proliferators may acquire the technique to reverse the isotopic denaturing. Thus, further study can be done to enhance the PR of RepU regeneration technique.