Investigation Of Steady-state Neutronics And Thermal-hydraulics Coupling For The Molten Salt Fast Reactor

Molten Salt Reactor?MSR?is the only liquid-fueled reactor in the Generation IV advanced nuclear energy system.It has considerable advantages in terms of inherent safety,excellent neutron economy,and feasibility of on-line refueling and reprocessing.Molten Salt Fast Reactor?MSFR?is one of the most potential reactor types among multitudinous MSRs due to it does not need graphite moderator,as well as has a better capability for achieving ²³²Th-²³³U breeding and transuranic?TRU?isotope burning than graphite-moderated MSR according to its characteristic of fast neutron spectrum.Multiphysics interaction during the operation of MSFR including neutron physics,thermal-hydraulic and structural material stress,among which the coupling of neutronics and thermal-hydraulics?THs?is the most significant.Therefore,the coupling study of neutronics and THs is of great significance for the design and safety assessment of MSFR.Firstly,in the core of the MSFR benchmark model,a large recirculation flow of the fuel salt is formed near the fertile blanket,it finally makes a hot spot occur in this region,which results in a great challenge to the temperature tolerance of material.Secondly,energy will be released by radiation capture reaction in the fertile blanket since the ²³²Th nuclide loaded in this region is exposed to the core neutron flux.Meanwhile,a small fission fraction will be located in this region since ²³³U is bred by ²³²Th.However,the heat deposited in the fertile blanket due to fission and neutron capture cannot be evacuated by the fuel salt through the blanket walls.Therefore,an external cooling system for the fertile blanket has to be considered in the reactor design.In this work,focusing on MSFR,a coupled code is developed using python programming language to establish a three-dimensional steady-state neutronics and THs coupling program suitable for MSFR by exchanging the power distribution,temperature and density distributions between OpenMC?Monte Carlo particle transport simulation code?and OpenFOAM?computational fluid dynamics software?.Simultaneously,in order to obtain the distribution of Delayed Neutron Precursor?DNP?in the core,an OpenFOAM solver suitable for DNP equation of MSFR was developed in this work to accomplish the simulation of distribution for DNP in turbulent flow fuel salt.Based on the coupling code,a benchmark model of MSFR is established,the convergence time and calculation accuracy of OpenMC and OpenFOAM are analyzed.Also,the effects of the number of neutonics region division and the different initial conditions on the k_eff,concentration of DNP,fuel salt velocity and temperature distributions are studied.The study result shows that different initial conditions have no effect on k_eff,and an alternative number and scheme of neutronics region division is recommended.Finally,the simulation results show a good agreement with the reference results of MSFR by comparison,which indicates that this coupled code can provide reliable results for the steady-state neutronics and THs coupling of MSFR.Based on the above-mentioned coupling code,in order to further conducting the neutronics and THs coupling research for MSFR optimized model,three different core optimized geometries and three cases of different number of external cooling loop for the fertile blanket are proposed in this work to carry out coupling calculation of neutronics and THs respectively.The three-dimensional velocity field,temperature field,and turbulent dynamic viscosity field of three different core geometries are analyzed.The results show that the hot spot and stagnation zones that appear in the upper and lower part of the core center,where is near the reflector,can be eliminated by curving both the top and bottom walls of the core.The results for fertile blanket show that the eight cooling loops with a total flow fate of 0.0555 m³?s^-11 guarantee the acceptable temperature distribution.