Design and performance analysis of passive residual heat removal system for a lead-cooled fast reactor

Lead-cooled Fast Reactor (LFR) has been chosen as one of the six Generation-IV reactor concept candidates due to its high performance in neutronics, thermal hydraulics and inherent safety features. Passive residual heat removal system (PRHRS) is a passive system that guarantees the residual heat removal of LFR even in the hypothetical beyond-design basis conditions. Based on a 1000 MWth lead-bismuth cooled fast reactor, the design and performance analysis of PRHRS were conducted using RELAP5 code. First, a PRHRS removing heat by Independent Heat EXchanger (IHEX) was designed, which utilizes natural circulation, gravity field and has the characteristics of high reliability and inherent safety. Secondly, the lead-bismuth heat transfer model was developed and verified based on RELAP5/MOD 4.0 code, as the heat transfer model of Pressurized Water Reactor (PWR) is not suitable for the lead-bismuth heat transfer calculation. The RELAP5 model of LFR was established and verified by comparison with design parameters. The PRHRS performance was investigated under Loss of Power (LOP) transient to assess the feasibility of the PRHRS design. The results demonstrated that the heat removal rate of the PRHRS removing heat by IHEX exceeded the core decay rate at about 5 h. The cladding peak temperature of the PRHRS reached 562 °C, which was below the limit (750 °C). Therefore, the PRHRS removing heat by IHEX has the capability to remove the LFR residual heat and has the characteristics of high performance and inherent safety, which can be used as an independent residual heat removal system for commercial LFR. The work provides reference for the design and performance analysis of LFR PRHRS in the future.