Development Of A Transient Analysis Program For Molten Salt Reactor

Molten Salt Reactor(MSR),belonging to one of the six advanced reactor types offered on the International Forum of the fourth generation nuclear energy system,has favourable features on economy,inherent safety and nuclear non-proliferation.With the development of MSR concept,it divides into two directions: one is the liquid fuel type MSR with the mix of liquid fuel salt and coolant salt.The other is the solid fuel type MSR with solid fuel elements and liquid coolant.Two designs employ some similar technologic characteristics,like high working temperature(~700 °C),low operating pressure(~1.0 MPa),high boiling point of coolant,negative temperature reactivity coefficient and so on.These feactures improve the inherent safety and economy of the system.Liquid fuel type MSR adopts the Th-U fuel salt which can achieve the fuel multiplication based on the thorium-uranium cycle and enlarge the utilization of thorium.Pebble bed fluorine salt cooled high temperature reactor,one branch of the solid fuel type MSR,adopts the fuel elements containing TRISO particles has high failure temperature(~1400 °C).Besides,the MSR concept can be coupled with online loading and water-free cooling technologies,etc.Under the guidance of miniaturized and modularized ideas,the development of small modular MSR can not only meet certain electricity demand,but also work flexibly as other energy type,such as heat supply,hydrogen production,methanol production and so on.Transient analysis of the MSR plays an important role on the safe operation of the reactor.The research of MSR is started in Oak Ridge National Laboratory(ORNL)in the 60 s of last century.Till now,many design tools have not been fully developed as light water reactor research tools which also have amounts of experimental data.In recent years,with the development of material technology and manufacturing industry as well as the diversified demand of nuclear energy development,domestic and foreign scientific research institutes have invested a lot into the research of molten salt reactor technology.Transient analysis and systemic simulation of MSR have been supported and developed on this basis.The systemic analysis of reactor is complex and the working characteristics and operational strategies of the system are often obtained by experiment,but it needs to invest a lot of money and manpower.With the development of the simulation technology,analysis of large systems is often through systemic codes.This can improve the efficiency of the system analysis work and reduce the cost and shorten the working cycle.In this paper,the operational characteristics of the molten salt reactor are preliminary analyzed and the equivalent calculation method of the related equipment is studied.Then,establish the general mathematical and physical model of energy system.A code named TREND(transient systematic analysis code for MSR)is developed and a series of transient analysis of MSR is simulated.This work is initialized from the basic law of conservation and uses the methods of staggered grid and semi-implicit finite volume difference method to solve the quality,momentum and energy conservation equations.The Gauss Seidel algorithm(G-S)is adopted to solve the network pressure matrix and update velocity of fluid,pressure distribution and other information.The discretization of heat structures are based on the finite volume method and the structure arrangement of the inhomogeneous material and non uniform distribution of internal heat source and three kinds of boundary conditions are under consideration.The power load is offered by the point reactor neutron kinetics model or power table read from the input card.The typical Runge Kutta method is used to solve the point reactor neutron kinetics model due to the rigidity of the equations.The thermal hydraulic phenomenon is more macroscopic than the neutron dynamics,so the time scale can be set more loosely.The fluid dynamics model and thermal structure model are coupled to solve to obtain the temperature distribution,the flow distribution and the pressure distribution of the system and provide a reference for analyzing the transient behavior of the system.The reactivity model has the factor of the control rod model,thus the reactor control logic can also be studied.In addition,the fluid temperature calculated by the thermal hydraulic model can be used as the input parameter of the power conversion module,which is used to calculate the energy conversion efficiency of the system.The calculation of the core power of the MSR needs to be considered separately due to the two different core design branches.For liquid fuel MSR,the fuel and coolant are mixed,so a decayed neutron dynamic term is added to the point reactor model to reflect the decayed neutron flow effect of the fuel salt in the loop.For PB-FHR,the fuel assemblies are located in the core so this can be approximated that there is no heat source existing outside of the core.However,the computational parameters of both point reactor models need to be derived from the neutron physical results of the MSR design.Besides,this paper summarizes the physical equation and properties of fuel,coolant,physical parameters of structural material,shell and tube type heat exchanger model,pump model,the core decay heat model,compressor,turbine model,pressure drop model and heat transfer calculation model.The TREND program developed in this paper can be used to analyze operation transient of MSR and study control logic and power conversion efficiency of energy system.User can model in input card conveniently and friendly.In this paper,the numerical solution of the basic model in the system analysis is contrasted with its analytical solution and the CFD commercial software and commercial transient analysis code RELAP5,which ensures that the computation results of the basic model will not deviate much from commercial programs.By comparing the calculation results of liquid molten salt reactor with the experimental results of MSRE pump startup and pump shutdown and comparing the numerical solution of solid point reactor with some other algorithms,the correctness of the point reactor neutron kinetics model calculation is ensured.The nuclear-thermal-coupling calculation of TREND is validated by the results of the early MSRE natural circulation experimental data.The paper also introduces the related work of molten salt experiments in which several modules of TREND are coupled with hardware equipment for the hardware-in-the-loop simulation,control technology and thermo-hydraulic experiment and so on.The control module is examined and used in the HTS nitrate loop of the SINAP and itoptimizes the original controller with the control technology and methods.This work also studies the feasibility of applying fuzzy control to control the temperature of the molten salt loop.The loop control and hardware in the loop test of the CIET experimental facility has been completed by coupling MATLAB and LabVIEW.It upgrades the function of the loop and laid the foundation for the subsequent development of hardware in the loop simulation and system simulation.