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NKS Programme Area:NKS-R
Research Area:Severe accidents
Report Number:NKS-475
Report Title:Source Term and Timing Uncertainty in Severe accidents NKS-STATUS Phase 2 report
Activity Acronym:STATUS
Authors:Sergey Galushin, Govatsa Acharya, Dmitry Grishchenko, Pavel Kudinov, Sara Ojalehto, Tuomo Sevón, Ilona Lindholm, Patrick Isaksson, Elisabeth Tengborn, Naeem Ul-Syed,
Abstract:The overall goal of the project is to generate a body of knowledge regarding the uncertainty in the magnitude of fission products release in case of a potential severe accident in Nordic nuclear power plants. The work aims to provide insights into the effect of various types of uncertainty on the source term predictions. Results of the work will be useful both for probabilistic and deterministic safety assessments as well as for emergency response applications. Within the second phase of the project sensitivity and uncertainty analyses were performed for a set of risk significant accident scenarios identified by the review of PSA L2 for a typical Nordic BWR within the first phase of the project. These scenarios include accident sequences that lead to filtered containment venting in case of a transient or LOCA, and accident sequences that lead to containment failure due to ex-vessel phenomena in case of a transient or LOCA. To perform sensitivity and uncertainty analyses, a review of available methods and tools for sensitivity analysis and uncertainty quantification was performed, selected methods were implemented in the simulation tools used in the project. Sensitivity analysis was performed to identify the most influential MELCOR code modelling parameters for selected accident scenarios. These parameters involved in the modelling of core degradation and relocation, fission products release from fuel, debris behaviour in the core region and vessel lower head, vessel lower head failure, fission products behaviour in the RCS and the containment, as well as modelling of the filter trapping, containment sprays and pool scrubbing. The most influential MELCOR code modelling parameters were then considered in quantification of uncertainty in the magnitude and timing of the fission products release to the environment.
Keywords:Severe accident, uncertainty quantification, MELCOR, Nordic BWR, fission prod-ucts, source term
Publication date:03 Jul 2023
Number of downloads:532
Download:pdf NKS-475.pdf
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