| The nodal Green’s function method transient program NGFM-C is under the second boundary condition and with rod cusping effect improved.In this thesis,the calculation of reactor core transient in time discretion method is researched,which makes the solving process of neutron spatial kinetics more accurate and rapid.It will also help in simulating time varied severe problems in reactor(such as eject rod,drop rod etc.)and providing more realistic three-dimensional power distribution of the reactor core.This thesis also study on adding transient poison concentration calculation module(mainly xenon,samarium)for simulating the process of neutron kinetics and improve the program.The time discretization method for the original transient calculation program NGFM-C is implicit difference method,which accuracy is one order and more time consuming.Moreover,in some cases the results are deviating from the true value.In order to improve the calculation accuracy,efficiency and stability,the diagonally implicit Runge-Kutta(DIRK)method which has higher order is explored.The mathematical principles and process of DIRK can be easily developed in the implicit difference method of original program NGFM-C.Firstly,the DIRK/NGFM-C transient calculation program is verified by the three-dimensional LMW transient benchmark problem,which proves the correctness and feasibility of the DIRK process in the program.Then,different orders of DIRK format is developed to calculate the three-dimensional transient benchmark problem.Compared with all the results,2S DIRK/NGFM-C program is selected which takes adventages in high order and time efficiency in simulating more complicated and time consuming problems of Qinshan reactor core.With the application of 2S DIRK/NGFM-C program,reactivity induced problems in the Qinshan reactor core such as rod ejection and rod drop are successfully calculated and analysed.The results are compared with the reference values which can provide useful references for reactor core control and safety.The time efficiency of the 2S DIRK/NGFM-C program is verified in dealing with the problems of large core transient calculation,that is,the calculation time is shorter in the same accuracy level.This thesis also study on adding transient poison concentration calculation module(mainly xenon,samarium)for the 2S DIRK/NGFM-C program to simulate the process of reactor shutdown and other process of poison change.We take Qinshan reactor core as example to calculate the concentration during the process of shutdown and distribution of equilibrium xenon,samarium.The results are also compared with calculation values of CASM04E/SIMULATE3,which indicate the development of the program is creditable. |
