Real-time Simulation Program Research Of Decay Heat Removal System In Pool-type Sodium Cooled Fast Reactor

As one of the representative reactors of Gen ? advanced nuclear energy systems,the pool-type sodium-cooled fast reactor has the better passive safety performance,according to the design principles of inherent safety,its' decay heat removal system could drive the natural circulation by density difference without pump to remove the heat in the core and keep the reactor safety.Based on the analysis of structural properties and thermal properties,a series of mathematical-physical models are set up,including the flow between subassemblies model,the heat exchange between hot and cool sodium pool model,the decay heat exchanger model,the air heat exchanger model,the pump idler turn model,the decay heat calculation model,the flow friction and heat transfer correlations model,and the thermo-physical properties of liquid sodium and air model,etc.The nodes are distributed according to the “Control body”method,the equations of heat exchanger are dispersed by fully-implicit second-order upwind scheme,Gear method is applied to solve the heat transfer model of coolant and thermal-hydraulic model in fuel pellet.Fourth Runge-Kutta method is used to solve the momentum conservation equation.The use of above methods could solve the equations accurately and effectively to reach the real-time simulation.The program of decay heat removal system is developed with modularized method by FORTRAN language.The simulation results indicated that in the steady state program,the errors of basic parameters are less than 1%.The program of decay heat removal system was verified by the station blackout accident.According to the accident sequence of station blackout accident,the establishment and development of natural circulation in the decay heat removal system was researched and analyzed,then calculating the other conditions including different inlet temperature of air and some equipments in the system can't work.The simulation results indicated that: At the early stage of station blackout accident,the temperature of coolant increased because the flow dropped sharply,then the natural circulation replaced the forced circulation gradually,the stable natural circulation would be established at 900 s after the accident;The decay heat removal system could protect the reactor effectively and removal the decay heat in the core,the maximum flow through the core was 12.3kg/s,and the peak temperature of the core could reach 570 ?,there is a big safety margin comparing with the sodium boiling temperature,It would take 10 hours to remove the decay heat completely after accident shutdown;The temperature of inlet air can influence the system properties,the heat exchange capability will increase with the decrease of inlet air temperature;The two sets of individual systems work effectively,and if some equipments in the system couldn't work,the system also can remove the decay heat to protect the reactor.The whole conditions in the paper can reach the fast real-time simulation,and the program has transplanted on the SimExec stage to connect with other systems.