Design Of A Passive Residual Heat Removal System For Msr And Heat Transfer Characteristics Of The Fuel Drain Tank Involved

Safety has to be firstly considered in the design of a reactor or system.Among all the problems as far as the safety is concerned,the key is that the residual heat could be efficiently removed.On the basis of the original residual heat removal system proposed by Oak Ridge National Laboratory(ORNL),a new modified air-cooled passive residual heat removal system(PRHRS)was proposed for the 10 MW molten salt reactor experiment after thoroughly scheme demonstration and discussion.Once the system is in operation,water in the bayonet cooling thimble absorbs the residual heat of the molten salt and evaporates;the steam is condensed in the air cooler and the condensate flows back into the bayonet cooling thimble via the steam drum under gravity,then a complete natural circulation is accomplished.In terms of the heat transfer characteristics of the bayonet cooling thimble and air cooler,etc,a calculation model was established and solved numerically in the code of C++.The calculated results were compared with the experimental results acquired in MSRE.Meanwhile,the operational characteristic of the air-cooled PRHRS was investigated,particularly on which the effects of the gas gap width and the steam riser width were evaluated.Furthermore,for satisfying the requirement of the system characteristic and temperature of the molten salt,an optimization operational scheme was proposed for the PRHRS.The results show that,such parameters as the power of bayonet cooling thimble and heat loss from fuel drain tank the PRHRS involved,the calculated results agree well with the experimental value from MSRE with errors within 10%.Compared with that of the gas gap,the width of the steam riser has an obvious effect on the natural circulation in the bayonet cooling thimble.Moreover,the air-cooled PRHRS can meet the design requirements of heat removal,and has a heat removal rate approximating to the decay heat generation rate,realizing the steady decrease in the temperature of the molten salt.The optimization analysis on the operational scheme show that the best way is to reduce the heat transfer element to 8 after running for 9 h and evacuate all of them after running for 57 h,This can postpone the adjustment time as well as the start-up of the fuel drain tank heater to the utmost on condition that the safety of the system could be ensured and the temperature of the molten salt changed in the safe range,and would also provide adequate emergency response time for the system.