| dc.description.abstract | Reprocessing of used nuclear fuel being the acquisition path for Pu and U by the proliferating states, the roles of intrinsic and extrinsic barriers to proliferation through this path need a deeper analysis. Denaturing of a fissile material, such as U or Pu, is one of the intrinsic barriers that renders the fissile material less suitable and less attractive for nuclear explosive device (NED) but does not affect its value as a source of nuclear energy for civilian energy uses. Isotopic denaturing using even-numbered isotopes is known to be less reversible than other denaturing methods. Pu may be denatured with higher fraction of Pu-238, and U may be denatured with higher fraction of minor U isotopes (U-232, U-234, U-236). Enriched reprocessed uranium (ERU) contains higher U-236 (due to its presence in the used fuel and its further enhancement after U-235 re-enrichment) compared to natural or reprocessed uranium. U-236, one of Pu-238 precursors, can enhance intrinsic barriers against Pu proliferation while practicing the recycling of used fuel. Until this time, the verification of the proliferation resistance (PR) of ERU has been conducted without a deeper understanding of the multi-isotope enrichment. Thus, to determine the concentration of U-236 in ERU, a matched-abundance ratio cascade (MARC) model is used. Following the MARC model, Monte Carlo N-Particle Transport (MCNP) computer code was used to simulate fuel burnup of a pressurized water reactor fuel assembly that uses ERU. Both, uranium enrichment and fuel burnup simulations allowed us to estimate the Pu-238 buildup in the ERU-based LWR fuel. Besides denaturing plutonium with Pu-238, reprocessed U (RepU) holds advantage over natural uranium in terms of discouraging production of highly enriched uranium (HEU). The presence of minor uranium isotopes U-232, U-234, and U-236 in the discharged fuel complicates the selective U-235 enrichment process. The MARC model was modified and applied to estimate the change in the amount of feed and lead time as U reprocessing and recycling are repeated. Pu is found denatured after 1st recycling of U and U is found denatured after 3rd recycling of U. Nevertheless, applying RepU for protected U production is questionable since recycling beyond the 2nd recycle is economically not feasible. In sum, it is hoped that the results of this study will be useful to support the reuse of recycled U for energy generation in the foreseeable future thereby result in efficiently using U resources and reducing the volume of deep geological repository. | en |
