Simulationon Neutron Space-time Kinetics For Accelerator Driven Sub-critical System

Accelerator Driven Sub-critical reactor(ADS)consists of coupling a spallationtarget,a high energy protonbeam accelerator anda sub-critical reactor core,comparing to the traditional Pressurized-water reactor,the external neutronsource of ADS reactor could tremendously increase non-uniform distribution extent of the sub-critical reactor core power and the complexity of the neutron behavior.In this paper,Monte Carlo transport theory was applied to the variables space and time separated framework of neutron space-time kinetics calculation for Accelerator driven sub-critical reactor.The improved quasi-static approximation was combined with Monte Carlo neutron transport program(IQS/MC)method.The shape function and kinetic parameters were calculated by Monte Carlo transport program,and the amplitude function was coupled with the lumped parameter thermal feedback model for neutron space-time kinetic process of ADS critical reactor with external source.Besides,the IQS/MC simulation calculation program with visualization operation platform for ADS sub-critical system was developed simultaneously,and this program consists of Monte Carlo program and kinetic parameters calculation module,IQS kinetics module,thermal feedback module and control interface program,which can achieve automatic calculation of the transient analysis process and the human-computer interaction step by step.The physical model of ADS was regarded as an example and beam increase,lifting fuel assembly,loss of the beams and loss-of-flow without scram weresimulated analysis based on this platform.The dynamics in two conditions of inserting beam and lifting fuel assemblywere simulated,the core total relative power and three-dimensional gird distributions of relative neutron fluence rate of energy group separated and relative power along with time were obtained.The calculated results of IQS/MC method and point reactor method were compared,the results agreed well with the relevant physics laws and those of foreign references,which verify that the IQS/MC method was suitably applicable to simulation of ADS neutron space-time kinetics.The dynamics in two conditions of loss of beams and loss-of-flow were simulated,Three-dimensional grid distributions of relative neutron flux of energy group were separated along time can be obtained,meanwhile the totally relative power,fuel temperature and outlet temperature of coolant at the core varied as the time can be also obtained.As known from the simulation results,the core relative power can make an immediate response when beam interrupt,and the fuel temperature and the outlet temperature of the coolant varied similarly with the time,but the time-response of the outlet temperature of the coolant was slower than the time-response of the fuel temperature.In conclusion,the point reactor kinetics model could underestimate relative power in ADS neutron kinetics calculation,which was a disadvantage to the nuclear reactor safety assess,but this problem can be avoided by IQS/MC method,so IQS/MC method was more suitable for ADS neutronics transient security analysis.