The Improvement Study Of Reactor Physics Real-time Simulation Model

Power distribution in nuclear reactor is the most intuitive parameter, which reflects theoperation state of the nuclear power plant. It is also related to the safety of nuclear reactor andnuclear security. We can realize the real-time simulation of the three-dimensional powerdistribution in core through the establishment of reactor core physics simulation model, whichcan be used to validate and improve the core design. It can provide technical support for thesafety and economic operation of reactor. The REMARK core physics real-time simulationprogram developed by GSE Company adopts square fuel assembly core physics model, whichcan be employed in the reactor physics simulation of PWR and this paper will modify theprogram on the basis of REMARK.Firstly, this dissertation establishes a core physics real-time simulation model of theQinshan Phase II nuclear power plant based on the real-time simulation model of theREMARK. The neutron kinetics model of three-dimensional and two groups with six groupsof delayed neutrons are applied and the solution of the model employs the improvedquasi-static approximation method. Thus, the neutron flux density is decomposed into theamplitude function and the shape function. The point kinetic equation is applied to slove theamplitude function and the finite difference method is employed to solve shape functions. Tosolve the difference equation of the shape function, the improved alternative direction implicit(ADI) method is applied. Through the modification of boundary conditions and cross sectionparameters of the original procedures in REMARK, we can achieve the purpose of theimprovement of REMARK. The outer boundary of reactor employs the albedo boundarycondition instead of the vacuum boundary condition. The fitting formula of cross sectionparameters is generated using stepwise regression method, and assembly two-group crosssection parameters are generated by fuel assembly burnup calculation code CASMO-4E.Secondly, preliminary study of nodal expansion method is conducted. Employ nodalexpansion method (NEM) instead of the improved quasi-static approximation method to solvethe neutron diffusion equation and the other methods are invariant. After the programmingand operation, we can get the simulation results and compare the results with the knownpower plant actual measurement data. Through the analysis of the simulation results and the accuracy of the nodal expansion method, we can verify the feasibility of applying the nodalexpansion method to the reactor physics simulation.The modified program was transplanted to SimExec platform developed by GSE andrealizes the reactor core physics simulation. Several burnup points are chosen to verify thesimulation results through comparing the on-line simulation results with the actualmeasurement data, which shows that the modified program can meet the requirements ofprecision and speed. The precision of the modified program is improved, which certifies themodification is effective. Relative error of nodal expansion method is larger and partial resultsof the simulation can not meet the requirement of the simulation precision, which shows thatthe program needs to be further improved. However, it proves that applying the nodalexpansion method to the core physical simulation to solve the neutron diffusion equation isfeasible.