Coupled Neutronics And Thermal-Hydraulics Simulation Methods For Nuclear Reactors

Nuclear reactor system is a complex system involving multiple physical phenomena.Multi-physics coupling simulation considering the multi-physics interaction can obtain the high-fidelity reactor state,which is the need of current reactor design and analysis.The design of new type reactors relies heavily on multi-physics coupling simulations to provide reliable analytical data due to lack of experimental and historical data.Most operating reactors can improve the reactor economy by reducing the safety margin based on high-fidelity multi-physics coupling simulations.Due to the need of current reactor design and analysis,high-fidelity multi-physics coupling simulation has become the focus of nuclear energy research.Monte Carlo codes are popular in coupled neutronics(including neutron transport and burnup)and thermal-hydraulics simulation.However,the inherent statistical error of Monte Carlo method may lead to numerical instability in the coupling process.Besides,the data mapping between the Monte Carlo neutron transport model which uses Constructive Solid Geometry(CSG)and other physical models is also a difficulty.In this paper,the research on the key problems of coupled Monte Carlo neutronics and thermal-hydraulics simulation was performed based on the multi-physics coupling framework of Super Multi-functional Calculation Program for Nuclear Design and Safety Evaluation(SuperMC).For coupled Monte Carlo neutron transport and thermal-hydraulics simulation,a general data mapping method based on the parametric-surface-represented entity clipping method was proposed,which can be applied to different thermal-hydraulic models.The stochastic approximation coupling strategy was used to decrease the impact of the inherent statistical error of the Monte Carlo method.Based on the multi-physics coupling framework of SuperMC,the coupled Monte Carlo neutron transport and thermal-hydraulics simulation integrated both Sub-Channel code SUBCHANFLOW and Computational Fluid Dynamics(CFD)code Fluent.The simulation results showed good agreement with the results calculated by other similar coupling codes,like MCNP/Fluent and MCNP/CTF,which well verified the capability of the coupling simulation.For coupled Monte Carlo transport-burnup and thermal-hydraulics simulation,an improved semi-predictive correction algorithm based on stochastic approximation was proposed to improve the tolerance of the burnup time-step size,which can also reduce the impact of the statistical error.The coupled Monte Carlo transport-burnup and thermal-hydraulics simulation was implemented based on the multi-physics coupling framework of SuperMC.The simulation results verified the improvement of the time-step size tolerance of the coupling strategy proposed in this paper.Finally,a space lithium-cooled nuclear reactor was analyzed and optimized by using coupled Monte Carlo neutronics and thermal-hydraulics simulations,which showed the comprehensive application ability of coupling simulation in practical problems.