Probabilistic safety assessment (PSA) is what most of the world outside the United States calls a probabilistic risk assessment (PRA). Same activity, same three levels, same tools: event tree analysis (ETA) for the accident sequences, fault tree analysis (FTA) for the systems inside them, and results reported as core damage frequency and release frequency. The IAEA safety guides use PSA throughout, as do most European and Asian regulators, while the US NRC uses PRA. There is no technical difference to chase here, only a vocabulary split, and both terms are worth knowing because vendor documents and international project work will use either one without explaining which they mean. The process industries run the same style of analysis under a third name, quantitative risk analysis (QRA).
Deep dive: For the free NUREG failure rate data that PSA work makes public, and how it maps onto SIF hardware, see Where Does the Data Come From? A Guide to Failure Rate Data Sources in Functional Safety.
Key Points
- PSA and PRA name the same analysis; the difference is regional vocabulary, not method.
- IAEA guidance is the international reference set, with separate safety guides for Level 1 and Level 2 PSA.
- Expect PSA in IAEA, European, and Asian documents, and PRA in NRC and US industry documents.
Example
A European utility submitting a Level 1 PSA and a US licensee submitting a Level 1 PRA are producing the same deliverable: a quantified core damage frequency built from event trees and fault trees.
See Also: PRA, probabilistic, ETA, FTA
Cited Sources
- International Atomic Energy Agency, Development and Application of Level 1 Probabilistic Safety Assessment for Nuclear Power Plants (IAEA SSG-3)
- Center for Chemical Process Safety (CCPS), Quantitative Risk Analysis (QRA), Process Safety Glossary