To retrieve the fuel debris in Fukushima Daiichi Nuclear Power Plants(1F),it is essential to infer the fuel debris distribution.In particular,the molten metal spreading behavior is one of the vital phenomena in nuclea...To retrieve the fuel debris in Fukushima Daiichi Nuclear Power Plants(1F),it is essential to infer the fuel debris distribution.In particular,the molten metal spreading behavior is one of the vital phenomena in nuclear severe accidents because it determines the initial condition for further accident scenarios such as molten core concrete interaction(MCCI).In this study,the fundamental molten metal spreading experiments were performed with different outlet diameters and sample amounts to investigate the effect of the outlet for spreading-solidification behavior.In the numerical analysis,the moving particle full-implicit method(MPFI),which is one of the particle methods,was applied to simulate the spreading experiments.In the MPFI framework,the melting-solidification model including heat transfer,radiation heat loss,phase change,and solid fraction-dependent viscosity was developed and implemented.In addition,the difference in the spreading and solidification behavior due to the outlet diameters was reproduced in the calculation.The simulation results reveal the detailed solidification procedure during the molten metal spreading.It is found that the viscosity change and the solid fraction change during the spreading are key factors for the free surface condition and solidified materials.Overall,it is suggested that the MPFI method has the potential to simulate the actual nuclear melt-down phenomena in the future.展开更多
To improve the efficiency and fidelity of the numerical analysis for cascade flutter, we propose an efficient scale-resolving simulation method dedicated to time-periodic flows by incorporating the harmonic balance ap...To improve the efficiency and fidelity of the numerical analysis for cascade flutter, we propose an efficient scale-resolving simulation method dedicated to time-periodic flows by incorporating the harmonic balance approach into the large-eddy simulation. This method combined convergence calculations of the steady-state problem based on the harmonic balance method for periodic components, and the nonlinear time-marching method for turbulent fluctuations. Using the proposed method, deterministic periodic components and stochastic turbulent fluctuations were calculated simultaneously, and the effect of turbulent fluctuations on deterministic periodic components was directly calculated without using turbulence models. In this paper, we explain the algorithm and feature of this simulation technique and present the results of the computation for channel flow excited in the streamwise direction as an analysis example using the proposed method. In order to validate the proposed method, an analysis of sinusoidally pulsating channel flow at the central friction-velocity Reynolds numbers Rer = 180 was conducted, confirming that the amplitude and phase of the mean velocity oscillation computed by the proposed method were in good agreement with those of the conventional LES. The present calculation achieved an order of magnitude improvement in computational efficiency compared to conventional LES.展开更多
文摘To retrieve the fuel debris in Fukushima Daiichi Nuclear Power Plants(1F),it is essential to infer the fuel debris distribution.In particular,the molten metal spreading behavior is one of the vital phenomena in nuclear severe accidents because it determines the initial condition for further accident scenarios such as molten core concrete interaction(MCCI).In this study,the fundamental molten metal spreading experiments were performed with different outlet diameters and sample amounts to investigate the effect of the outlet for spreading-solidification behavior.In the numerical analysis,the moving particle full-implicit method(MPFI),which is one of the particle methods,was applied to simulate the spreading experiments.In the MPFI framework,the melting-solidification model including heat transfer,radiation heat loss,phase change,and solid fraction-dependent viscosity was developed and implemented.In addition,the difference in the spreading and solidification behavior due to the outlet diameters was reproduced in the calculation.The simulation results reveal the detailed solidification procedure during the molten metal spreading.It is found that the viscosity change and the solid fraction change during the spreading are key factors for the free surface condition and solidified materials.Overall,it is suggested that the MPFI method has the potential to simulate the actual nuclear melt-down phenomena in the future.
文摘To improve the efficiency and fidelity of the numerical analysis for cascade flutter, we propose an efficient scale-resolving simulation method dedicated to time-periodic flows by incorporating the harmonic balance approach into the large-eddy simulation. This method combined convergence calculations of the steady-state problem based on the harmonic balance method for periodic components, and the nonlinear time-marching method for turbulent fluctuations. Using the proposed method, deterministic periodic components and stochastic turbulent fluctuations were calculated simultaneously, and the effect of turbulent fluctuations on deterministic periodic components was directly calculated without using turbulence models. In this paper, we explain the algorithm and feature of this simulation technique and present the results of the computation for channel flow excited in the streamwise direction as an analysis example using the proposed method. In order to validate the proposed method, an analysis of sinusoidally pulsating channel flow at the central friction-velocity Reynolds numbers Rer = 180 was conducted, confirming that the amplitude and phase of the mean velocity oscillation computed by the proposed method were in good agreement with those of the conventional LES. The present calculation achieved an order of magnitude improvement in computational efficiency compared to conventional LES.
