Numerical Simulation On Four-loop Pwr Atasymmetric Operation Conditons Based On CFD

The pressurized water reactor(PWR) with multiple loops may have abnormal working conditions with coolant pumps out of running in some loops. At present, there are great limitations on some traditional transient thermal hydraulic calculation codes and experimental studies, detailed information of the complex three-dimensional(3D) coolant mixing and flow distribution, temperature and pressure distributions in Reactor Pressure Vessel(RPV) on asymmetric operation conditions cannot be resolved. In this paper, the reactor core is simplified by using porous media model, and the dynamic boundary conditions are developed and then embedded into the 3D numerical simulation software(FLUENT) code through utilizing the functionalization of user-defined function(UDF) in FLUENT, and thus the dynamic numerical simulation of PWR at asymmetric operatio n conditions is achieved. So far an effective and credible numerical simulation method of four-loop PWR at asymmetric operation conditions is established preliminarily.Firstly, the computational models, governing equations and numerical methods adopted in the numerical simulations on the flow in RPV of reactor are introduced. And the porous media theory are described in detail.Secondly, parameters of porous media model and reactor heating computation program are established by performing numerical simulation only in the reactor domain. Then, simulations have been performed in the modeled RPV of VVER 1000 working at different operation conditions. The pressure losses of coolant flowing through the core are obtained and compared with the available operation pressure data on hand. It indicates that the computational conditions are accurate and reasonable for the current CFD numerical simulations. The results of stead-state simulation at different asymmetric operation conditions show that the corresponding parameters of each loop present strong symmetry at four-loop running condition; on the contrary, the global parameters present non-symmetry at three-loop or two-loop asymmetric operation conditions, because the backflow coolant of invalid loop has a certain influence on pressure, velocity in the RPV and mass flux distribution of the coolant at the inlet of reactor core.Finally, the dynamic boundary conditions are developed and then embedded into FLUENT to simulate the transient working conditions between different asymmetric operation states. For these cases, pressure losses across the reactor, mass flux of each loop, mass flux distribution of the coolant at the inlet of reactor core and the force acting on the support column were obtained. The results show that pressure losses across the reactor are connected with flow characteristic without external regulation, if the shape of the porous core is fixed; when the asymmetric operation condition changes from one to another, the more invalid loops, the greater the inequality degree of mass flux distribution of the coolant at the inlet of reactor core; but the direction of whole force acting on the support column i s unchanged and the value varies weakly. It indicates that the transient between different asymmetric operation states has little influence on the force acting on the support column.