Innovative design of uranium startup fast reactors

Abstract

Sodium Fast Reactors are one of the three candidates of GEN-IV fast reactors. Fast reactors play an important role in saving uranium resources and reducing nuclear wastes. Conventional fast reactors rely on transuranic fuels from reprocessing facilities, which are not available in the U.S. Thus, deployment of fast reactors requires decoupling from reprocessing facilities. This motivates the design and deployment of Uranium Startup sodium Fast Reactors (USFR) on a once-through fuel cycle in order to facilitate the transition to fast reactors by reducing their plant costs and increase capacity factor. Three different fuel types including uranium carbide (UC), metal (UZr) and uranium oxide (UO₂) are investigated and analyzed using the ERANOS code for potential use in USFR designs. A key enabling factor is use of high-albedo MgO or Zr reflectors in place of fertile blankets to reduce uranium enrichment and improve non-proliferation resistance. The different compositions in different fuel types result in different neutronic performance. The softer spectrum and lower allowable fuel volume fractions of oxide fuel have shorter fuel cycle length due to reactivity constraints, whereas fast neutron fluence plays an important role in determining the fuel cycle length in metal cores due to the harder spectrum. Moderators are deliberately added in the metal fuels to lower the fast neutron fluence. Carbide cores have a slightly harder neutron spectrum than oxide cores and a larger achievable fuel volume fraction. USFRs using all three fuel types (UC, U0 2 and UZr) have lower fuel cycle cost (6.27, 6.09 and 5.77mills/kWhe) and comparable uranium consumption (0.50, 0.55, and 0.53kgNatU/MWde) compared with typical LWRs (6.39nills/kWhe and 0.53kgNatU/MWde). All USFR designs have maximum neutron fluence below 5E23n/cm². All three USFR designs have pressure drop below 0.7MPa and maximum temperature below the limit for each fuel type. Both carbide and metal fuel have excellent passive safety performance. It is concluded that the USFR approach is a competitive way to accelerate fast reactor development.