Application of FFTBM for sensitivity study

摘要

The uncertainty quantification of best estimate codes is typically accompanied by a sensitivity analysis, in which the influence of the individual contributors to uncertainty is determined. The objective of this study is to demonstrate that the fast Fourier transform based method (FFTBM) and improved FFTBM by signal mirroring (FFTBM-SM) can be used for the sensitivity analysis when one parameter is varied at a time. The sensitivity study was performed for the LOFT L2-5 test, which simulates the large break loss of coolant accident. There were 14 participants in the BEMUSE (Best Estimate Methods - Uncertainty and Sensitivity Evaluation) programme, each performing a reference calculation and 15 sensitivity runs of the LOFT L2-5 test. These calculations were used to determine the sensitivity for upper plenum pressure, primary side mass inventory and rod surface temperature. The results suggest that FFTBM and FFTBM-SM are especially appropriate for a quick assessment of a sensitivity analysis in which several calculations need to be compared. Finally, the results show that with the FFTBM-SM the analyst can also get the time dependent picture of the input parameter influence to the results.