Uncertainty and sensitivity analysis of the ASTEC simulations results of a MBLOCA scenario in a generic KONVOI plant using the FSTC tool.

• Karlsruhe Tool for Uncertainty and Sensitivity Analysis (KATUSA) tool (as part derived from the Fast Source Term Calculation (FSTC) tool) is described; • Medium Break Loss-of-Coolant Accident (MBLOCA) scenario simulated with the ASTEC code up to the basemat rupture; • Consistency of the simulations results is proven – using two sets of simulations: up to the basemat rupture and up to the lower head vessel failure + 6000 s; • Results for the release of the different fission products (FPs) into the environment and containment are presented; • Spearman correlation values for different "FPs release – input parameter" pair are presented; • Role of the input parameters governing aerosols behavior shown for the later stages of the severe accident (SA); • Influence from the pre-correlation set for the input parameters is discussed. This paper presents the results of uncertainty and sensitivity (U&S) analysis of Medium Break Loss-of-Coolant (MBLOCA) severe accident (SA) scenario simulations performed with the ASTEC code with a generic input deck prepared for a KONVOI-1300 nuclear power plant (NPP). The analysis was done with the in-house Fast Source Term Calculation Tool (FSTC) (currently: KArlsruhe Tool for Uncertainty and Sensitivity Analysis (KATUSA)). Part of the presented here results – analysis of MBLOCA scenario simulations up to the basemat rupture - were already shown at the ERMSAR conference in 2022. Here an extension related to the analysis of shorter MBLOCA simulations (up to 6000 s after lower head vessel failure (LHVF)) and investigation of the influence from adding correlations between uncertain input parameters is given. The analysis allows to identify which uncertain input parameters influence the release of fission products (FPs) in the containment and environment at the different stages of SA progression. [ABSTRACT FROM AUTHOR]