An Initial Study on Modeling the United States Thermal Fuel Cycle Mass Flow Using Vensim

Abstract

According to current forecasts, nuclear power plant construction and nuclear-generated electricity production is projected to increase in the next half-century. This is likely due to the fact that nuclear energy is an ‘environmental alternative’ to fossil fuel plants that emit greenhouse gases (GHG). Nuclear power also has a much higher energy density output than other alternative energy sources such as solar, wind, and biomass energies. There is also growing consensus that processing of low- and high-level waste, LLW and HLW respectively, is a political issue rather than a technical challenge. Prudent implementation of a closed fuel cycle not only curbs build-up of GHGs, but can equally mitigate the need to store nuclear used fuel. The Global Nuclear Energy Partnership (GNEP) is promoting gradual integration of fuel reprocessing, and deployment of fast reactors (FRs) into the global fleet for long-term uranium resource usage. The use of mixed oxide (MOX) fuel burning Light Water Reactors (LWR) has also been suggested by fuel cycle researchers. This study concentrated on modeling the construction and decommissioning rates of six major facilities comprising the nuclear fuel cycle, as follows: (1) current LWRs decommissioned at 60-years service life, (2) new LWRs burning MOX fuel, (3) new (Gen’ III+) LWRs to replace units and/or be added to the fleet, (4) new FRs to be added to the fleet, (5) new reprocessing and MOX fuel fabrication facilities and (6) new LWR fuel fabrication facilities. Our initial work [1] focused on modeling the construction and decommissioning rates of reactors to be deployed. This is being followed with a ‘mass flow model’, starting from uranium ore and following it to spent forms. The visual dynamic modeling program Vensim was used to create a system of equations and variables to track the mass flows from enrichment, fabrication, burn-up, and the back-end of the fuel cycle. Sensible construction and deployment rates were benchmarked against recent reports and then plausible scenarios considered parametrically. The timeline starts in 2007 and extends in a preliminary model to 2057; a further mass flow model scenario continues until 2107. The scenarios considered provide estimates of the uranium ore requirements, quantities of LLW and HLW production, and waste storage volume needs. The results of this study suggest the number of reprocessing facilities necessary to stabilize and/or reduce recently reported levels of spent fuel inventory. Preliminary results indicate that the entire national spent fuel inventory produced over the next ∼50 years can be reprocessed by a reprocessing plant construction rate of less than 0.07 plants/year (small capacity) or less than 0.05 plants /year (large capacity). Any larger construction rate could reduce the spent fuel inventory destined for storage. These and additional results will be presented.