Numerical Study Of Flow Behavior Of Lead-bismuth In Fuel Assembly With Wire Spacer

As the good physical properties for heat transfer and neutronics, Lead-Bismuth Eutectic (LBE) is a priority candidate material for the coolant and spallation target for the ADS (Accelerator Driver Sub-critical System), and the Lead-bismuth cooled reactor has become the main development direction of the fourth generation reactors. As the core component of nuclear reactor, fuel assembly directly affects the safety, economy and reliability of the reactor. In the fuel assembly of heavy liquid metal cooled fast reactor, the wire spacer helically wound on the fuel rod with identical pitch, which maintain appropriate rod-to-rod clearance and created channels of coolant. Wire spacers can produce cross flow which enhancing the heat transfer between the coolant in different channels and improving the temperature uniformity of coolant, but it also lead to higher friction factor and more hot spot. Numerical analyze the influence of wire spacers on the flow in the fuel assembly is of great importance to the improvement of thermal-hydraulic characteristics.According to the preliminary scheme of the10MW nature circulation Lead-bismuth cooled reactor designed by the FDS team, detailed flow field and temperature field distribution of the LBE in the fuel assembly have been analyzed with one of the Computational Fluid Dynamics (CFD) codes FLUENT in this paper. Acquired the important parameters such as friction coefficient、temperature gradient and hot spot; Comparative analysis between the calculation value and the theoretical value of the pressure drop between the inlet and outlet of the fuel assembly; Analyzed the impact of wire pitch on the thermal hydraulic characteristics of the fuel assembly; Analyzed the impact of the degree of wire spacers on the flow field and the temperature field distribution at the outlet of the fuel assembly. These results can provide valuable references for the design and optimization of the fuel assembly of lead-bismuth cooled reactor.The results showed that the highest temperature of LBE in the fuel assembly of the10MW nature circulation Lead-bismuth cooled reactor was701K, the average axil velocity was0.205m/s, the maximum temperature of UO2was1007K, which meet the thermal and hydraulic design requirements; As the exist of the wire spacers, the temperature distribution of the LBE in the outlet of the fuel assembly was more uniform; Among the analyzed models of three different pitch and degree of the wire spacers, the friction factor was lowest when the pitch of the wire spacer was550mm, the outlet temperature of LBE was more uniform when the degree of the wire spacer at the outlet was30°.