Sensitivity Assessment of the ASTEC Code Results for a Severe Accident in a SFP by Using the SUNSET Tool

The present work focuses on the sensitivity assessment of simulation results for a severe accident scenario in the Spent Fuel Pool of Fukushima Daiichi Unit 4, using a simplified case study. The analysis is performed using the ASTEC code, based on an input deck developed by INRNE-BAS under the EU Horizon 2020 MUSA project. A probabilistic approach is applied for the propagation of input uncertainties using the SUNSET statistical tool. A total of 100 ASTEC simulations are conducted, enabling the estimation of 95%/95% probability and confidence levels for key outputs using Wilks' formula. The paper outlines the step-by-step application of the ASTEC/SUNSET methodology, its adaptation, and the main results.