Study Of Passive Residual Heat Removal System Design For Lead-based Fast Reactor

Lead-cooled Fast Reactor(LFR)was chosen as one of the six Generation-IV reactor concept candidates due to excellent performance in neutronics,thermal hydraulics,chemical and inherent security features.Under the accident conditions,a large amount of the core residual heat is a significant risk to the LFR reactor safety.It is important to conduct a study of Passive Residual Heat Removal System(PRHRS)to improve the inherent safety of LFR.Three kinds of the PRHRSs of a lead-bismuth cooled fast reactor with a power of 1000 MWth were studied,including lead-bismuth heat transfer model development and verification,the design,performance analysis,influencing factors and performance comparison analysis.The detailed were as follows:1)Based on the benchmark of lead-bismuth heat transfer model of OECD/NEA Lead-Alloy-Cooled Advanced Nuclear Energy Systems(LACANES),the appropriate heat transfer models were developed and added to the RELAP5/MOD 4.0 code,since the heat transfer model of Pressurized Water Reactor(PWR)is not suitable for the lead-bismuth heat transfer calculation.The lead-bismuth heat transfer model was verified by the simple pipe model test,which laid the foundation of PRHRS design and performance analysis.2)According to passive safety design approach,three kinds of the PRHRSs were designed,where the heat removal characteristics were studied by using RELAP5/MOD 4.0 code.The results showed that:The heat removal rate of three kinds of the PRHRSs removing heat by Steam Generator(SG),Independent Heat EXchanger(IHEX)and Reactor Vessel(RV)exceeded the core decay rate at about 0.6 hours,5 hours and 48hours,respectively.The cladding peak temperature of three kinds of the PRHRSs reached 490 ℃,562 ℃ and 743 ℃,respectively,which were below the limit(750 ℃).The results indicated that the design of three kinds of the PRHRSs satisfy the design goals.3)The optimization design suggestions were given by studying the parameters sensitivity of three kinds of PRHRSs.The results showed that:For PRHRSs removing heat by SG and IHEX,increasing the heat transfer area and decreasing system response time can enhance the heat removal capacity of PRHRS.However,increasing the height difference of cold and heat source center and decreasing loop resistance have little effect on the heat removal capacity of PRHRS.For PRHRS removing heat by RV,increasing chimney height and heat transfer area,and decreasing gap width between main and safety vessel can enhance the heat removal capacity of PRHRS.However,increasing the vessel wall emissivity and decreasing system response time have little effect on the heat removal ability of PRHRS.4)The scheme design suggestions were given by the performance comparison of three kinds of the PRHRSs.The PRHRS removing heat by SG is suitable as an independent residual heat removal system for a high power LFR/commercial reactor,or operation in the early phase of the accident.The heat removal capacity of PRHRS removing heat by IHEX is suitable as an independent residual heat removal system for a medium-power LFR/demonstration reactor.However,the heat removal capacity of PRHRS removing heat by RV is suitable as an independent residual heat removal system for a small power LFR/research reactor or operation in the late stage of the accident.In order to enhance the safety of LFR,it is recommended to use two or more kinds of PRHRSs.