Improvement on natural uranium utilisation in heavy water-moderated molten salt reactor using radial blanket

Abstract

Heavy water moderated-molten salt reactor (HWMSR) is a novel concept in which heavy water is used as the neutron moderator in lieu of graphite. Excellent neutron economy of heavy water moderator allows HWMSR to use natural uranium as its fuel, foregoing the need for uranium enrichment. Studies regarding HWMSR typically assumes a single fluid stream with identical fuel conduit size throughout the core. This study expands that premise by analysing the performance of HWMSR fuelled by natural uranium with virtual one-and-half fluid stream, using 10% fuel volume fraction (VF) in the narrow fuel conduit and 22.5% fuel VF in blanket conduit. The variation ranges from no blanket until three outer blankets. Neutronic and burnup calculations were conducted using MCNP6.2 code and ENDF/B-VII.0 neutron cross section library. From the calculation results, it was observed that the temperature coefficient of reactivity (TCR) for all variations worsen over time, and only one variation remains negative until the end of cycle (EOC). Fuel cycle length in larger blanket layer numbers is significantly longer, better fertile conversion, and lower fissile consumption. The plutonium vector degraded quickly, so that it becomes impossible to divert. Overall, it is suggested that HWMSR that works using natural uranium be given larger blanket layer numbers to maintain safety and improving performance.