The Study And Optimization Design Of The Bayonet Cooling Tube In The Passive Decay Heat Removal System For The Fuel Drain Tank To The 373MW Molten Salt Reactor

Molten Salt Reactor(MSR)is one of the most advanced candidate reactor modes in fourth-generation nuclear system.It has advantages of good economy,high safety,recyclable and flexible fuels etc.Safety is one of the most important issues in MSR design.Decay heat removal system is one of the most important systems in guaranteeing safety of reactor shutdown.Based on a large numbers of domestic and international related literatures,analyzing and summarizing several decay heat removal system designs of classic reactors,taking decay heat removal system of MSRE and DRACS of Mark-1 as references,this research takes decay heat removal system of the 100 MW level MSR as a study object,introducing an initial design which can be applied to the 100 MW level MSR.The bayonet cooling thimble is a component with triple casing design.Flowing cooling water inside casing exchanges heat with high temperature molten salt outside casing,density difference generated by cooling water heated and gasified provide driving force of natural circulation inside bayonet cooling thimble.This thesis analyzes heat exchange process between molten salt and casing,and natural circulation process of cooling water inside casing,designs a program by MATLAB,which is capable to calculate steady state parameters of bayonet cooling thimble.Usability of this program is examined by FLUENT and experiment designed by Harbin Engineering University.This thesis analyzes performance of bayonet cooling thimble in steady state and influence,providing a calculation basis for later optimal design.According to the calculation results of MATLAB calculation program,this research optimizes bayonet cooling thimble design by FLUENT,analyzing temperature variation of molten salt and key parts of bayonet cooling thimbles under different bayonet cooling thimble arrangements and different arrangement spacing with decay heat curve.The influence generated by air gap change?different tube heights ?emissivity to the walls of the air gap and edge effect of the drain tank also is analyzed.Conclusion shows that on the premise of the wall surface highest temperature of heat exchange temperature under 977.4K,organizing unit bayonet cooling thimbles as a square arrangement,taking 0.095 m as spacing value will achieve the most economical situation;reducing air gap shows little improvement in heat transfer enhancement,therefore,0.0043 m spacing design is retained;the outer wall temperature positively correlates with the height of the bayonet cooling thimble;the circular edge of the drain tank will influent the arrangement of bayonet cooling thimble;the heat transfer capability of the bayonet cooling thimble raises with the increase of the emissivity to the walls of the air gap.While the drain tank is 4m wide and 2m high and the emissivity to the walls of the air gap is 0.5,the minimum number of the bayonet cooling thimble is 1721.