Research On Direct Simulation Method For Neutron Continuous-energy Spacial Kinetics

Neutron spacial kinetics, which is one of the vital and complex subjects in the field of nuclear reactor analysis, must solve the time-dependent neutron transport equations or the neutron diffusion equations as the approximation to the transport equations, with the explicit representation of delayed neutrons by numerical methods. The latter is simpler in form and requires less computer capability to be solved. Hence, the diffusion theory has been widely used in reactor analysis. However, due to its inherent approximation, there are some limitations for the transient analysis methods and codes based on this theory.With the development of the computer hardwares and the numerical calculation techniques, the research focus has been gradually transferred from the diffusion theory to the transport theory. Recently, the transient calculations based on the transport theory have been made great progresses, and some relevant transient analysis codes have been developed. These researches show that under the current computational condition it is feasible to solve nuclear reactor kinetics problems by the transport theory.After investigating the existing transport transient analysis methods and codes, a new method for transient, three-dimensional neutron transport problems is put forward. This thesis makes the detailed reseach on this method, including the theoretical model, algorithm establishment, design of calculation framework and development of the relevant transient analysis code. In this method, transient problems are solved by simulating the dynamic behaviors of neutrons and precursors of delayed neutrons during a transient process. And it is for all-purpose use since it gets rid of various approcimations which are always necessary to other methods. For instance, it is based on the transport theory rather than the diffusion theory, its origin is stochastic method, it adopts continuous-energy neutron interaction data instead of multi-group data, it adopts continuous treating instead of discretization for time variable. So it is suitable for various transient problems, different energy spectrum, complex geomertry and material composition. In order to emphasize the characteristic of continuous simulation for time variable, this method is called the direct simulation method (DSM).Combining with the 973 program—the fundamental research of key scientific problems for supercritical water reactor (SCWR), several SCWR fuel assemblies are adopted to verify the DSM and the code. Under different transient conditions, the variations of neutron flux distribution along with time are calculated by the new transient analysis code TMCC (Transient Monte Carlo Code). And some verification and analysis of the calculated results are presented. Finally, a series of typical nuclear reactor transient processes caused by the adjustment of control rod position are simulated.Based on the integral research of DSM, further work on random number generators and criticality calculation are carried out. For the former, a new improved algorithm is introduced. About the criticality calculation, a critical calculation module based on the conventional methods is developed and the coupling with the subsequent transient calculation is completed. Moreover, considering with the special requirement for the criticality calculation used in DSM, a new method is preliminarily studied and the relative code is developed.