Research On Coupling Schemes Of Burnup Calculation And On-The-Fly Therment On Thermal Scattering Based On RMC

Monte Carlo(MC)method is widely applied in analysis and caculation of nuclear system,and becomes more and more attractive in nuclear industry.Large-scale MC calculation with high fidelity is increasing turning into main tool for reactor simulation.Burnup calculation underlies reactor computating,and can be used for comprehensive calculation through which coupling with hydrauclic and material codes.Sevral aspects of MC burnup are researched in detail in this paper composed with following content.Coupling problem of MC burnup calculation,involving coupling schemes and numerical stability is researched in this paper.For coupling schemes are analyzed and developed in Reactor Monte Carlo Code(RMC),which is developed by REAL lab of Department of Engineering Physics in Tsinghua Univeristy.Two different predictorcorrector methods are researched and developed,the first method corrects results of MC burnup calculation based on nuclear density,while the second one based on reaction rate,i.e.one group effective cross section and neutron flux.In addition,high order predictorcorrector with sub-step method is researched,by using which the efficiency of MC burnup calculation can be notably improved.For numerical stability,method used for preventing xenon oscillation with variable power density in short burnup steps is proposed in this paper,and shows stronger applicability.Moreover,rim effect in burnup calculation caused by spatial self-shiedling and caculation method of online refueling in RMC are researched as well.Traditional method used in MC burnup calculation to take spatial self-shiedling effect into consideration is dividing fuel pin into several annular rings,which results in extra memory requirement and computing time.An effective cross section method is proposed in this paper to solve such problem.Meanwhile,online refuling burnup calculation function based on psudo nuclide is developed in RMC to simulate online fuel feed and fission poision removal in new generation reactor like Molten Salt Reactor(MSR).Research on thermal scattering treatment including seperated and on-the-fly treatments by which can be used for reducing memory requirement of nuclear data used in MC burnnup calculation to improve capability of MC code in large-scale problem.In this paper,traditional thermal scattering data processing method is researched firstly and related module of nuclear data code,Thermc,is developed.This code can calculate ACE(A Compated ENDF)formatted thermal scattering data directly from evaluated nuclear data files.In addition,on-the-fly treatment on thermal scattering data based on online sampling is researched.Using phonon spectrum of moderator material,probability density function and cumulative probability function can be obtained from independently developed code SabFit,which is developed in this paper to carry out least square method to fit temperature dependent cumulative probability function into polynomials and calculate related fitting coefficients to fabricate distribution law of momentum and energy transfer number.Those cumulative probability function,consequently,used in RMC,to describe state of out thermal neutron.This on-the-fly method of thermal scattering data treatment can be used to reduce memory requirement by 10% with high accuracy and efficiency.