Numerical study on flow and heat transfer characteristics of helical fuel in lead-bismuth reactor

[Background] The Lead-Bismuth-cooled fast Reactor (LBR) is one of the advanced Generation IV nuclear energy systems. The majority of the LBR concept design uses wire-wrapped fuel assembly. The helical fuel, a new type of nuclear fuel, can be used in potential LBR, which can enable fuel self-supporting of and improve heat transfer. [Purpose] This study aims to study the flow resistance, convective heat transfer, and transverse mixing characteristics of helical fuels in LBR and evaluate the comprehensive flow and heat transfer performance of different helical fuels. [Methods] The study employs computational fluid dynamics (CFD) to compare the resistance coefficient (f), Nusselt number (Nu), and comprehensive performance evaluation factors of various 2×2 helical fuel bundles, thereby assessing their flow and heat transfer characteristics. Additionally, the flow sweep mixing parameters and temperature distribution of a 3×3 helical fuel bundle are analyzed to evaluate the transverse mixing characteristics. Furthermore, the comprehensive performance evaluation factors of three types of helical fuel bundles are compared to assess their overall flow and heat transfer performance. [Results] The results demonstrate the following key findings: (1) The comprehensive performance of helical fuels is significantly influenced by the blade-to-valley radius ratio. Specifically, an increase in this ratio leads to a degradation in overall performance. (2) Among the helical fuel configurations examined, the four-blade helical fuel exhibits superior convective heat transfer performance. (3) When comparing the flow sweep mixing parameters across the three types of helical fuels, it is observed that the flow sweep mixing parameters at the inner/inner subchannel interface are larger for helical fuels with a higher blade-to-valley radius ratio. This condition also results in a more uniform temperature distribution across different subchannels. [Conclusions] The results show that the four-blade helical fuel is more suitable as the preferred nuclear fuel for the lead-bismuth reactor.