Molten Salt Reactor Safety Analysis Under Different Working Conditions

Molten salt reactor is the only liquid fuel reactor in the fourth generation nuclear power system,so the safety analysis of molten salt reactor is different from other types of reactor.This paper analyzes the safety of three stages of start-up,disturbance and accident in molten salt reactor.Firstly,the reactor kinetic equation in the start-up stage is modified to make it suitable for molten salt reactor with liquid fuel.The modified point reactor kinetic equation is solved by analytical method.The numerical method is used to verify the analytical solution,and the results show that the analytical solution is same with the numerical solution.The solution of the point reactor kinetic equation without modified is higher,so it is no longer suitable for start-up analysis of molten salt reactor.Based on the solution of the point reactor kinetic equation with modified deduce the expression of molten salt reactor cycle,derives physical startup neutron multiplication curve,derives the relationship between reactivity insertion rate and neutron density.Provide safety analysis reference for start-up of molten salt reactor.Secondly,the local disturbance of molten salt reactor is studied using MCNP(Monte Carlo and Photo Transport Code)software.The optimal radial position of the control rod is obtained,and the disturbance of the axial center of the control rod has the greatest influence on the effective multiplication coefficient of molten salt reactor.The influence of local temperature disturbance on molten salt reactor is obtained: the Doppler effect occurs at the axial both ends has a greater influence on the core.Finally,based on finite element analysis software,the change of each parameter in molten salt reactor is studied when accident happened.The temperature field,precursor concentration distribution and neutron flux distribution in molten salt reactor were studied.The results show that when the accident of losing of flow happened the outlet temperature increases slowly at first.But when it higher than 1000 K it will grow exponentially.Precursor concentration distribution will change because of the loss of flow.It has little effect on the neutron flux distribution.when graphite expanded,the temperature of graphite will rise,the thermal neutron flux will increase,the thermal neutron distribution become out of shape.