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NKS Programme Area:NKS-R
Research Area:Risk analysis and probabilistic methods
Report Number:NKS-345
Report Title:Deterministic-Probabilistic Safety Analysis Methodology for Analysis of Core Degradation, Ex-vessel Steam Explosion and Debris Coolability
Activity Acronym:DPSA
Authors:Pavel Kudinov, Sergey Galushin, Dmitry Grishchenko, Sergey Yakush, Yvonne Adolfsson, Lisa Ranlöf, Ola Bäckström, Anders Enerholm, Pavel Krcal, Anna Tuvelid,
Abstract:This reports summarizes the experience achieved within the NKS-DPSA project during 2014. The aim of the project is to develop the methodology for application of Integrated Deterministic-Probabilistic Safety Analysis (IDPSA) with PSA/DSA to the Nordic nuclear energy industry and regulatory needs. We further develop a Risk Oriented Accident Analysis Methodology (ROAAM) framework that demonstrates how dynamic behavior in NPPs can be better included in safety analyses. The methodology is developed and demonstrated through analysis of the relocation of the core melt to the lower plenum, as initial conditions for the melt-vessel structure interactions, melt release and ex-vessel steam explosion and debris bed coolability in Nordic BWRs. The influence of timing in PSA level 1 sequences and possible recovery actions on the amount and properties of the melt in the lower head are addressed. It is shown that IDPSA results can be used to refine and improve the PSA in several ways. One example is the analysis of recovery of core cooling, where IDPSA has provided usable information regarding the timing and possibility of core coolability (re-flooding). This information can be used as a basis material for the HRA, to re-define the binning of plant damage states as well as provide probabilities for failure of coolability. The analysis performed for phenomena such as steam explosion shows interesting results that are relevant for the PSA-modelling. The analysis provides insights regarding under which conditions each phenomenon should be modelled and can therefore influence the sequences for which the phenomena is modelled. The results may also be used as one input to the quantification of phenomena. The analysis can be developed to further facilitate the use in PSA. Experiences from performed studies are summarized in the report as well as suggestions of areas which need further investigations.
Keywords:IDPSA, PSA, DSA, BWR, Severe accident, MELCOR, MAAP, core degradation, steam explosion
Publication date:03 Jul 2015
ISBN:ISBN 978-87-7893-427-7
Number of downloads:2776
Download:pdf NKS-345.pdf
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