S. Skutnik

Determining Optimal Used Fuel Allocation Strategies

A key challenge in fulfilling the U.S. federal government’s obligations under the Nuclear Waste Policy Act is in the transition of used nuclear fuel (UNF) storage away from at-reactor storage and t...

Evaluation Of Covert Plutonium Production From Unconventional Uranium Sources

The potential for a relatively non-advanced nation to covertly acquire a significant quantity of weaponsgrade plutonium using a gas-cooled, natural uranium-fueled reactor based on relatively primitive early published designs is evaluated in this article. The economic and technical issues that would influence the design decisions of a covert Pu production program are considered. Several unconventional uranium acquisition approaches were explored. Methods for extracting uranium from enrichment tails, seawater, and coal ash sources were considered. The evaluation indicated that uranium extraction from coal ash or in-situ leaching from underground deposits could be performed in economical manner that might be difficult to detect by the international community. These two methods were estimated to be within the technical capabilities of an under-developed nation. Calculations performed using the Monte Carlo N-Particle code (MCNP) showed that extracting uranium from enrichment tails would not be a technically feasible source for reactor fuel fabrication because the U concentration inside the enrichment tails would not be high enough to maintain criticality in the relatively unsophisticated reactor design considered. The SCALE code package was used to perform reactor physics and depletion calculations used to evaluate the effect of different combinations of uranium irradiation time and reactor power density had on plutonium production rates and isotope concentrations. The results of these simulations were used to estimate the desirability of the modeled plutonium for use in a weapon with published material attractiveness figures of merit. All the modeled reactor conditions produced material that was highly attractive for use in a nuclear weapon. Historical examples of early gas-cooled reactors were used to examine the complexity associated with building various gas-cooled reactor designs. These examples were compared to simulated reactor conditions. The choices that a covert unsophisticated nuclear weapons program might consider when designing a reactor were evaluated. An air-cooled design was found to be a simple and cost effective solution for a group interested in producing a small number of significant quantities (8 kg) of plutonium. 1 Chvala et al.: Evaluation Of Covert Plutonium Production From Unconventional Uranium Sources Published by Trace: Tennessee Research and Creative Exchange, 2016 International Journal of Nuclear Security, Vol. 2, No. 3, 2016

An Examination of Simplification and Uncertainty on Material Attractiveness Evaluation for Proliferation Resistance Assessment

The effect of simplifications in nuclear fuel depletion analysis as well as the effect of cross-section uncertainties were evaluated as to their impact upon material attractiveness for weapons diversion purposes. The effect of simplified depletion models for material attractiveness evaluation was evaluated through a comparison of pressurized water reactor fuel for several benchmark cases, using experimentally measured values along with a two-dimensional lattice physics model (TRITON) and a point depletion model (ORIGEN-S). Simplifications such as the use of the ORIGEN-S depletion libraries and assumptions of homogeneous core enrichment were found to have a negligible impact on material attractiveness evaluation, particularly relative to uncertainties in experimental measurements; additionally, simplified irradiation power histories do not introduce unacceptable errors into the attractiveness evaluation. Finally, the overall sensitivity of material attractiveness and associated uncertainty was found to be greater for transuranic mixtures compared to plutonium as a function of both burnup and decay time; however, associated uncertainties are generally small and not prohibitive to material attractiveness discrimination. As a result, the use of simplified depletion models such as ORIGEN-S appears to be well justified for use in material attractiveness evaluation for proliferation resistance studies.