Study On Neutronic Characteristics Of Dispersed Granular Media And Burnup Algorithm

Dispersed particulate fuels and poisons have received extensive attention due to their many excellent properties and have broad application prospects in light water reactors.Different from conventional homogeneous materials,they are a kind of dispersed particulate media with special structure,which leads to different performance of fuel and poison.From the perspective of reactor physics,the in-depth study of the neutronic characteristics of the dispersed particulate media and the full use of its potential advantages are of great significance for promoting the development of accident tolerant fuels and advanced reactors.In addition,it is found in the research that the calculation amount is too large and the calculation efficiency is low when solving the fine burnup of the dispersed particulate media.There are certain shortcomings in the existing calculation methods,and further development is urgently needed.Therefore,this paper mainly focuses on the neutronic characteristics of the dispersed particulate media and the related burnup algorithm,and carries out the following research work.Firstly,starting from the preliminary application research of dispersed particulate media,carry out neutronic characteristic analysis for the PWR assembly loaded with dispersed particulate media,evaluate the performance and characteristics of fuel assembly,and analyze the effect of dispersed particulate poison on fuel assembly performance.The study found that the life-time of the dispersed particulate fuel is insufficient,and the reactivity level decreases rapidly and greatly.Thus,it is necessary to appropriately increase the enrichment degree,the concentration and size of fuel particles.Reducing the cell pitch to reduce the level of slowing,could improve its negative feedback and inherent safety.In addition,the reactivity can be effectively controlled by adding a dispersed particulate poison with a particle concentration of0.2% and a radius of 300 μm,making the new assembly approach critical with a substantially parallel trend throughout its lifetime.It is preliminarily demonstrated that the dispersed particulate media has great neutronic characteristics based on the application of PWR assembly,and has broad development prospects.Secondly,in order to further study the neutronic characteristics of the dispersed particulate media,based on the difference model comparison method,the spatial effect research is carried out at the pin-cell level.Compare and study a series of models that limit the difference in spatial structure characteristics,demonstrate the changes of fuel and poison neutronic characteristics caused by the difference in spatial structure characteristics,and explore the internal influence mechanism of the spatial structure of the dispersed particulate media on the fuel and poison neutronic characteristics.Studies have shown that the spatial effect of the dispersed particulate fuel will increase the fuel neutron breeding efficiency and self-shielding effect,thereby increasing the overall reactivity and neutron flux level,slightly increasing the fuel consumption rate,but not causing microscopic stratification.The spatial effect of the dispersed particulate poison is more serious.It increases the self-shielding of the poison,reduces the effective crosssection of the poison in the initial burn-up period,and reduces the consumption rate of the poison,thereby prolonging its life and controlling the reactivity for a long time.In addition,serious microscopic stratification occurs during the burnup process,which brings certain challenges for accurate numerical simulation.Thirdly,in order to cope with the above challenges,a multi-scale coupled burnup calculation method is proposed.By coupling the microscopic spherical model and the macroscopic pin-cell model,the fine solution problem of dispersed particulate media is transformed into a fast solution problem of simple homogeneous media.The problem of large amount of calculation and high grid density in the process of solving the fine burnup of the dispersed particulate poison in the global scope is solved,and the macroscopic and microscopic characteristics of the dispersed particulate poison in each burnup period are accurately and efficiently characterized.Compared with the collision probability method,the calculation speed is increased by about 2 times while ensuring the calculation accuracy.It provides a new idea for solving the burnup problem of the dispersed particulate media.Finally,aiming at the efficiency of burnup calculation,a new Krylov subspace burnup acceleration algorithm is proposed.By searching the optimal solution in a new Krylov subspace based on GMRES iteration,the calculation scale and amount of calculation of the target system are reduced,so as to achieve the purpose of speeding up the solution of the burnup equation.Meanwhile,residuals are strictly controlled during the new subspace projection process,for ensuring computational accuracy.With the help of preconditioning technology and restart technology,the new algorithm can converge more efficiently and stably.The verification results show that compared with the algorithm in the global space,the calculation speed is increased by more than 4 times while ensuring the calculation accuracy,and the efficiency problem when solving the burnup equation is effectively solved.