A methodology for preliminary probabilistic multi-unit risk assessment

Tero Tyrväinen, Anna Häggström, Ola Bäckström, Kim Björkman

Research output: Book/ReportReport


In this study, a methodology is outlined to estimate the importance of multi-unit accidents for a site with more than one reactor unit. The suggested approach is based on: - Identification of dependencies - Qualitative and quantitative screening - Estimation of frequencies/probabilities for screened in dependencies - Calculation of the Multi-Unit Core Damage Frequency (MUCDF) or Multi-Unit Large Early Release Frequency (MULERF) using primarily conditional quantification of single unit models (together with the frequency/probability of the dependence) - Sum of the MUCDF/MULERF for the identified dependencies to estimate the total MUCDF/MULERF The approach is considered a conceptual approach, and there are a number of outstanding issues that could be studied further. Most importantly, the approach needs to be validated using full scope PRA models.
Original languageEnglish
PublisherVTT Technical Research Centre of Finland
Number of pages29
Publication statusPublished - 2017
MoE publication typeD4 Published development or research report or study

Publication series

SeriesVTT Research Report


  • multi-unit probabilistic risk assessment
  • dependencies

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    Tyrväinen, T., Häggström, A., Bäckström, O., & Björkman, K. (2017). A methodology for preliminary probabilistic multi-unit risk assessment. VTT Technical Research Centre of Finland. VTT Research Report, No. VTT-R-00086-17 http://www.vtt.fi/inf/julkaisut/muut/2017/VTT-R-00086-17.pdf