Status of Site-Level (Including Multi-Unit) Probabilistic Safety Assessment Developments

NEA/CSNI/R(2019)16
Adobe Acrobat PDF Document - on 7/1/21 at 5:30 PM
- Adobe Acrobat PDF Document on 4/19/21 at 10:40 AM

Two important lessons learnt from the March 2011 Fukushima Daiichi nuclear power plant (NPP) accident were: 1) there can be significant interactions between multiple co located radiological sources (e.g. reactor units, spent fuel pools or dry fuel storage facilities) on a shared NPP site in response to concurrent or consequential initiators; and 2) the timing of concurrent accident sequences involving multiple site radiological  sources can challenge shared structures, systems and components, and resources available for severe accident management and emergency response.

Since this accident, the international nuclear safety community has been exploring whether the traditional single-unit PSA approach is sufficient for assessing the radiological risk associated with accident scenarios for multi-unit sites and if there is a need for an integrated multi-unit PSA (MUPSA) or site-level PSA approach that includes consideration of concurrent accidents involving co-located radiological sources. The international nuclear community has since made significant efforts to enhance the simulation and assessment of such multi source accident scenarios.