Investigation On Method Of Characteristics For Reactor Core Calculation

At present,the core structure of the reactor system is designed more and more complexly,such as the BWR which is designed increasingly complexly and the MOX-UO₂mixedly loading PWR.Local effects produced in the core are more significant.Differences of neutron characteristics in the components are intensifie.As the the core space changes,the neutron spectrum becomes more complex.Considering approximately that homogenization parameter is only the function of component type and has nothing to do with its specific location in the reactor core,existing"two-step"core physics calculation error has been growing.Direct solution of the reactor core neutron transport equation eliminates the"two-step"major errors and has been widespreadly concerned.Method of characteristics（MOC）can solve the fine structure of the neutron transport equation in any geometry,becoming one of the main research directions in core transport calculations.This paper studies the core calculation using method of characteristics on the basis of the Dragon program.First,for different treatments of the source terms in method of characteristics,linear source approximation method is added to Dragon program in which flat source approximation has been applied.To verify the correctness and validity of the linear source,the widely used square and hexagonal components are computed in two-dimensional and three-dimensional methods.Then the small reactor SMART core is calculated in three-dimensional method on the basis of the characteristic line parameter sensitivity analysis and the effect of acceleration method test.The computing results,the time required for the calculation process and the storage space are analyzed.Finally,for the long computing time in three-dimensional core calculation,2D MOC/1D S_N coupling method is used for solving the core transport equation.2D MOC/1D S_Ncoupling calculation process is studied.Programming the one-dimensional SN calculation program and combining it with Dragon code,the core SMART is carried out by 2D MOC/1D S_Ncoupling calculation.The results of the study show:the linear approximation method using the coarse grid and loose control characteristic parameters can obtain higher computing accuracy.And if the accuracy is similar with the accuracy of flat source approximation,the linear source approximation requires less computing time and storage space,verifying that adding the linear source approximation method to the Dragon code is effective;Argument quadrature in characteristic controlling parameters has the greatest impact on the results;In Dragon code,while using the ACA,SCR,TMT acceleration method in MOC,the acceleration effect is the best.The MOC obtain the fine core neutron flux distribution,but the calculation time is very long and it can not meet the engineering application.Particularly the long characteristic method has great limitations to large core computing.In the 2D/1D three-dimensional core coupling calculation,the required computer memory,storage and computing time have been significantly improved.The MOC using 2D/1D coupling calculation is more conducive to core computing under current conditions.