The Neutronics Analysis of Heat Pipe Cooled Traveling Wave Reactor Designs With High-Assay Low-Enrichment Uranium and Natural Uranium

Abstract The heat pipe cooled traveling wave reactor (HPTWR) is a novel design. This paper firstly presented a HPTWR design featured with a traditional traveling wave reactor core, which consists of high-assay low-enrichment uranium (HALEU) section (20%) and natural uranium section (0.725%), or ignitor section and breeder section. The core was a hexagonal prism and assembled with more than a thousand of separated UN fuel elements. Each fuel element was a smaller hexagonal prism with a heat pipe channel in the center. A lithium and Mo/Re heat pipe was used in the current design. The neutronics calculations were performed using Monte Carlo code RMC with heat pipes, cladding and UN fuel had a same operational temperature (1700 K). And the results showed that at the beginning of the cycle reactivity is high, and Keff has reached 1.36, and power is concentrated in the ignitor section with nearly zero power in the far end of breeding section. Then an improved HPTWR design is proposed to limit the swing of keff less than 1%, and distribute the power more evenly by reducing the enrichment difference between ignitor section and breeder section with similar core geometry. The HPTWR using natural uranium can reach 100MWth of power and 350 years of refueling cycle, and the improved HPTWR can reach 70MWth and more than 40 years of refueling cycle.