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NKS Programme Area:NKS-R
Research Area:Severe accidents
Report Number:NKS-411
Report Title:Phenomena Threatening Containment Integrity in Deterministic and Probabilistic analyses and integration of PRA levels 1 and 2
Activity Acronym:SPARC
Authors:Anna Nieminen (ed.), Veikko Taivassalo, Magnus Strandberg, Tero Tyrväinen, Ilkka Karanta,
Abstract:Phenomena threatening the BWR containment integrity were assessed both deterministically and probabilistically. Studies related to establishing a temperature-based dryout criteria for a debris bed were continued evaluating the influence of friction models. Agreement between the VTT and KTH results was improved after implementing the same friction model as in DECOSIM into Fluent. Deterministic steam explosion analysis was performed to study the effect of RPV breaking location on dynamic pressure load on lower drywell wall. The resulting explosions were stronger in comparison to the previous central break cases. Probabilistic modelling of steam explosions is very challenging because uncertainties related to the phenomenon, especially triggering of explosions, are very high. Currently, it is a good idea to use conservative probabilities in PRA. It could be studied if explosion triggering probabilities could be estimated based on some physical parameters calculated by deterministic software tools, but plenty of development work and analyses are needed before well-justified probabilities can be estimated. The development of simplified PRA models of a BWR plant was also continued by extending previously developed level 1 and level 2 models were extended and integrated so that it is possible to list most important event tree sequences, initiating events and basic events with regard to radioactive releases.
Keywords:Debris bed coolability, Fluent, steam explosions, MC3D, PRA
Publication date:04 Oct 2018
ISBN:ISBN 978-87-7893-500-7
Number of downloads:1187
Download:pdf NKS-411.pdf
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