Fuel cycle performance of the Fort Saint Vrain reactor

All modern fuel cycle analysis studies have not considered the historically operated high-enriched uranium (HEU) and thorium (Th) fuel cycles. This represents a significant gap in the literature as these reactors were operated both in the United States and internationally. The work discussed here fills that gap by determining the performance of the Fort Saint Vrain high enriched uranium thorium fuel cycle with respect to natural uranium resource utilization, high-level waste, low-level waste, radioactivity, land use, water use, and CO 2 production. The Department of Energy (DOE) Office of Nuclear Energy (NE) Evaluation and Screening (E&S) study provides information on several different figures of merit for many nuclear fuel cycles employing advanced reactors; however, the study does not include information on high-enriched uranium fueled systems. Fort Saint Vrain and Peach Bottom are the only commercially operated high temperature gas-cooled reactors in United States history, and they operated with a high enriched uranium‑thorium fuel cycle. Determination of the performance of the high enriched uranium thorium fuel cycle is a novel contribution due to the lack of similar investigations in the E&S study as well as in the literature. To understand the performance of the Fort Saint Vrain once-through fuel cycle, a full-core Serpent model with equilibrium fuel masses was created. This was depleted for a length of time determined by the quadratic reactivity model using 6 batches. The resulting burnups and discharge masses were used to compare performance to once-through cycles from the E&S study. There is a gap in similar modeling of the Fort Saint Vrain equilibrium core in the literature, as well as the necessary concentration of information to facilitate modeling Fort Saint Vrain. Once-through cycles from the E&S study for a pressurized water reactor using low-enriched uranium fuel (EG01), a high temperature gas-cooled reactor using high-assay low-enriched uranium fuel (EG02), and a high temperature gas-cooled reactor using high-assay low-enriched uranium and thorium fuel (EG05) were compared to Fort Saint Vrain. The results show that compared to the HTGR and HTGR-Th fuel cycles, Fort Saint Vrain performed better for the natural uranium required, 36.8% less than the HTGR and 33.2 less than the HTGR-TH, CO 2 produced, 21.8% less than the HTGR and 20.4% less than the HTGR-Th, and land use metrics, 20.2% less than the HTGR and 18.7% less than the HTGR-Th. For spent nuclear fuel and high level waste (SNF&HLW) produced, the Fort Saint Vrain fuel cycle produced 27.3% more mass than the HTGR and 2.8% more mass than the HTGR-TH. Compared to the LWR fuel cycle Fort Saint Vrain performed well requiring similar mass of natural uranium, 2.4% more, and land, 4.7% less, as well as producing similar amounts of CO 2 , 2.9% less, but producing 46.5% less SNF&HLW. The activity at 100,000 years is the main disadvantage of the Fort Saint Vrain fuel cycle. Mainly due to the presence of U-233 in the discharged SNF&HLW, Fort Saint Vrain produced significantly more activity at 100,000 years, with activity being 990.5% more than the LWR, 770.2% more than the HTGR, and 143.7% more than the HTGR-TH. The results show that Fort Saint Vrain had benefits regarding mass of natural uranium required and environmental impact; however, its main drawback was a high level of long term activity largely driven by the high U-233 content of the spent nuclear fuel. This suggests that the HEU-Thorium fuel cycle should be operated as a continuous recycle fuel cycle for which the thorium fuel was originally intended.