Thermal Hydraulics And Safety Analysis Of A Supercritical Carbon-dioxide Modular Small Reactor

The supercritical carbon-dioxide reactor is promising and has attracted widespread attention in the last two decades.But it is still in the stage of conceptual design and experimental verification.Thus many works such as thermal hydraulics and safety analysis are still being executed.Based on the extensive investigation,this paper focuses on the thermal hydraulic,safety limits and limiting safety system settings,safety analysis of typical accident by establishing mathematical physics models and programming.Based on that,the supercritical carbon dioxide modular micro reactor(MMR)originally designed by Korea Advanced Institute of Science and Technology(KAIST)was researched as the object with the developed safety analysis program.The main research contents of this paper are as follows:1)The mathematical and physical modeling of KAIST MMR was established,and a safety analysis program ASSCR for supercritical carbon dioxide reactors was developed using the FORTRAN programming language.2)MMR engineering hot channel factors were derived to considerate the influences of engineering uncertainties.The safety limiting regime and permissible operation regime were calculated using ASSCR,and limiting safety system settings were obtained.The results show that the main constraint on the maximum power varies with the mass flow,and at the rated flow,the maximum allowable temperature of the cladding is the main limiting factor for the maximum core power.3)In view of the uncertainties of the factors including thermophysical properties of materials,heat transfer coefficient,flow disparity factor,sensitivity of LSSS power was evaluated.The results show that the descending order of sensitivity is convection heat transfer coefficient,carbon dioxide specific heat capacity,flow disparity factor,carbon dioxide thermal conductivity,carbon dioxide viscosity,cladding thermal conductivity,among which convection heat transfer coefficient,flow disparity factor and material thermal conductivity lead to the greatest effect on LSSS power.4)Some typical transient unprotected accidents were calculated,including loss of flow,reactivity insertion accident,loss of heat sink,and overcooling.Then loss of flow accident with scram was calculated,because maximum core outlet temperature was beyond its safety limit.The results show the cladding and fuel temperature have not exceeded their safety limits,indicating that MMR has good safety characteristics under the above accidents;however,the maximum core outlet temperature is close to or exceeding its safety limit,which indicates the material of pipe is the key constraint on transient performance.Besides,the loss of flow accident may be the most threatening for the MMR system.This paper’s preliminary research on the supercritical carbon-dioxide modular small reactor has certain reference significance for further research and application in the future.