Probabilistic Safety Assessments (PSA), which was introduced in the 1970s as complement to deterministic safety analysis methods, is a well-established tool that supports design and safety assessment of nuclear facilities, and risk-informed decision-making. The wide use of PSA techniques demonstrate that they complement deterministic safety analyses well. However, traditional PSA approaches also have their limitations, specifically in meeting the challenge of identifying realistic scenarios in complex and dynamic systems.
Therefore, the IAEA is encouraging Member States to explore the use of Advanced Probabilistic Safety Assessment (PSA) to get a deeper view of a nuclear power plant’s risk profile than that offered by traditional PSAs, thereby contributing to decision-making that can strengthen safety. The Agency is offering trainings, workshops, events and forthcoming publications to highlight the potential of Advanced PSAs.
“Advanced PSA approaches and applications, such as considering the dynamic human machine interaction in the evolution of an accidental situation have been discussed for quite a while – it is now time to test and apply them extensively in practice” said Cornelia Spitzer, Section Head of the IAEA’s Safety Assessment Section.
The development of Advanced PSAs began decades ago to broaden the perspective gained from the static PSAs. Advanced probabilistic approaches provide a more accurate view of plant behaviour in response to initiating events. Compared to conventional assessments, advanced PSAs include more realistic modelling of safety systems and structures, as well as the human-machine interactions. In addition, the use of assumptions in conventional assessments can lead to distorted risk profiles, which in turn might create obstacles for effective decision-making.
“Understanding the risk profile for a nuclear installation is the ultimate goal of the PSA, and it needs to yield as realistic results as possible. Advanced PSAs offer a way to get such results,” Spitzer said.
Participants in an IAEA-organized international workshop on Advanced PSA approaches and applications held in September 2019 in Alkmaar, the Netherlands, exchanged experiences, insights and proposals related to the method. The 36 participants in workshop noted that more practical application of advanced PSAs, experience feedback as well as consideration of further development and harmonisation is needed.
“It’s important to recognize that with improvements in technical knowledge and analysis capabilities, current solutions can always be improved,” said Nathan Siu, Senior Technical Adviser for Probabilistic Risk Assessment in United States’ Nuclear Regulatory Commission and a panellist at the workshop.
Discussions at this workshop and other IAEA events on ongoing actions related to dynamic modelling, software reliability analysis methods, passive system reliability assessment approaches, the use of ageing trend analysis results are contributing to revisions of the IAEA Safety Standards and the development of supporting technical documents.
