[en] The reactor coolant pump is the key equipment of nuclear power plant. The pump-induced pulsation will induce the vibration of main components of primary equipment, which is one of the main reasons for component fatigue failure. For AP1000 nuclear power plant, the special layout of RCP and SG aggravate this influence. A simplified modeling is established for the pump-induced pulsation of heat transfer tubes of AP1000 steam generator, and the calculation results can be used for the fatigue analysis and assessment for the heat transfer tubes of steam generator. (authors)

[en] The purpose of the present paper is to evaluate the validity of CFD, especially Large Eddy Simulation (LES), to simulate the OECD/NEA benchmark experiment MATiS-H. The 5 × 5 rod bundle with a split-type spacer grid is simulated by both steady and transient simulation and the numerical results of time averaged and root-mean-square velocity field are compared to the experimental data. It is demonstrated that LES can better describe the mixing turbulent flow velocity field than the FANS method. The mesh sensitivity analysis further reveals that LES with fine mesh is more appropriate for analyzing the turbulent flow field in the rod bundle with spacer grids. LES results help understand the mixing turbulence characteristics with the mixing effect evaluation in transient. The simulated flow field data can also be of value for mechanical evaluations such as flow-induced vibration and grid-to-rod-fretting phenomenon. (authors)

[en] In this study, a modified boron tracking model which takes into account the mass diffusivity caused by the turbulence flow is developed and embedded into RELAP5 code based on second order Godunov method. This method is validated by the analytical solution of linearized Burges question. At last, the sensitivity studies of the inlet velocity and refinement of node scheme are performed, which demonstrates the model's capability of capturing turbulent diffusion transient under low velocity condition and the adaptability to different node schemes. (authors)

[en] Large eddy simulation (LES) of the swirling flow in the rod bundle subchannels with spacer grids are presented. According to the rod bundle flow benchmark experiment, the 5×5 rod bundle with a split-type spacer grid is simulated by this transient simulation with a fine hybrid mesh. Mean velocity components, RMS (root mean square) velocity components and turbulent kinetic energy profiles at different locations downstream the mixing vanes are compared between the experiment and simulation results. LES results can reproduce the mixing turbulent flow velocity field well. We also have studied the influence of the mixing vanes' bending degree on the subchannel flow structures by using LES to simulate the 3×3 rod bundle with the typical PWR spacer grid. The mixing vanes' bending degree is modified to 35deg and 40deg based on the original spacer grid, whose mixing vanes' bending degree is 30deg. The larger bending degree produces a stronger mean coolant mixing effect, while larger pressure loss and fluctuation come together with this effect. The increased pressure loss would generate additional flow resistance, and larger fluctuation of coolant flow would make the mixing effect unstable, as well as would cause flow-induced vibration and grid-to-rod fretting phenomena. The LES method is a viable tool to optimize the spacer grid design and provide transient flow field data for mechanical analysis. (author)

[en] A transient analysis code TAPIRS was developed to analyze the behavior of the heat pipe cooled space reactor power system based on the SAIRS models. Three typical accidents are analyzed using TAPIRS. The results show that the fuel temperature is below a safe limit under the control drum failure, the AMTEC failure and partial loss of the heat transfer area of radiator. This demonstrates that the reactor system is with the characteristics of self-stabilization ability under accident conditions. (authors)