Study On The System Analysis Code And The Safety Characteristics Of Liquid Fueled Molten Salt Reactors

The molten salt reactor is one of the generation IV reactors,which has remarkable advantages as good economy,inherent safety,on-line feeding and on-line post-processing.The nuclear fuel of liquid fueled molten salt reactors flows in the primary loop,which makes the neutronics and thermo-hydraulic characteristics of liquid fueled molten salt reactors different from traditional solid fueled reactors.Safety analysis is always an important issue with the development of nuclear energy.The task of safety analysis is to study the safety characteristics of reactors under different conditions.It is an important part of the reactor design and construction process.Development of liquid fueled molten salt reactor system safety analysis code and construction of liquid fueled molten salt reactor safety assessment method are an important basis for the analysis of reactor safety,which is of great significance for the guarantee and improvement of reactor safety and reliability.In this paper,RELAP5/MOD4.0 code is extended based on the point kinetic model,thermohydraulic model of liquid fueled molten salt reactors and the solving algorithm of delayed differential equations.The correctness of the model and the extended code is verified by the experimental datum of the pump start-up,the pump coast-down,the natural circulation and the reactivity perturbation transients of the Molten Salt Reactor Experiment(MSRE)at Oak Ridge National Laboratory(ORNL).The extended code provides the tool support of liquid fueled molten salt reactor safety analysis.Meanwhile,the initial events of liquid fueled molten salt reactors are classified according to the reports of domestic HAF,HAD and international IAEA,NRC and ORNL,and on the basis of the classification method of the initiating events of pressurized water reactor,sodium-cooled fast reactor and high temperature gas-cooled reactor.The safety limits of the liquid fueled molten salt reactor are determined according to the properties of the reactor material.The maximum temperature of fuel salt and graphite moderate in the core are achieved by the conservative single-channel model considering the uncertainty.Therefore,the whole safety assessment method of liquid fueled molten salt reactor is constructed,which lays the foundation of safety analysis of liquid fueled molten salt reactor.In order to further verify the applicability of the extended code and the safety assessment method,the safety characteristics of the low power 2 MWt experimental molten salt reactor TMSR-LF1 and the high power 2250 MWt molten salt breeder reactor MSBR system are modeled and analyzed respectively.The transient responses of reactivity changes,the transients of heat dissipation increasing and decreasing at secondary molten salt loop are simulated in order to obtain safety characteristics of the reactor under different operating conditions.The results show that the safety margin of TMSR-LF1 is larger than that of MSBR.The temperature of TMSR-LF1 exceeds the safety limits under uncontrol withdrawal transient of the control rod,control rod accidentally broken transient and transient of lost of force flow at secondary molen salt loop.The temperature of MSBR exceeds the safety limits under uncontrol insertion transient of the control rod,transient of accidentally supercritical during fuel addition,transient of lost of force flow at secondary molten salt loop and transient of increasing load demand.It is necessary to take timely measures to avoid damage of the reactor.The results of the analysis show that the extended RELAP5/MOD4.0 code and the proposed safety assessment method are applicable to the safety assessment of liquid fueled molten salt reactors at different power levels.Development of liquid fueled molten salt reactor system analysis code based on RELAP5/MOD4.0,establishment of the safety assessment method and their application analysis have an important engineering reference for further engineering design and safety analysis of liquid fueled molten salt reactor of Advanced Nuclear Energy Innovation Institute of Chinese Academy of Sciences.