Uncertainty and Sensitivity Analyses of Source Term Estimates during an Unmitigated SBO Sequence in a PWR-1000 Reactor

The Management and Uncertainties of Severe Accidents (MUSA) project is focused on the testing, adaptation, and use of Uncertainty Quantification (UQ) and sensitivity methods for the application in Severe Accident (SA) analysis. An Uncertainty and Sensitivity Analysis (UaSA) of source term (ST) estimates in a Best Estimate Plus Uncertainty (BEPU) calculation of an unmitigated Station Black-Out (SBO) occurring in a 3-loop PWR-W has been conducted by CIEMAT in collaboration with University of Pisa. The results of the analysis provided some major insight. The ST magnitude is affected by a small uncertainty band. Sensitivity analysis did not point at any phenomenon of outstanding significance; however, the time of fuel failure and the diffusional release of radionuclide from fuel have been found to affect the ST to the environment.