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Assessing Safety Margins and Avoiding Cliff-Edge Effects at NPPs by Applying Option 4 from SSG-2

IAEA Headquarters, Vienna, Austria

14 May 2013

Background

NSNI Seminar_14 May.pngIn 2009, the IAEA published the Specific Safety Guide SSG-2 on Deterministic Safety Analyses for Nuclear Power Plants. This Guide addresses four options for the application of deterministic safety analyses. The first option uses conservative codes/models and conservative Initial and Boundary (I&B) conditions and has been used since the early days of civil nuclear power. Option 2 uses realistic codes/models but with conservative I&B conditions. Option 3 uses realistic codes/models and realistic I&B conditions and therefore also needs to consider the associated uncertainties. Today, it is known as the Best Estimate Plus Uncertainty (BEPU) option.

Option 4 is not developed in the SSG-2 document. The Safety Guide only indicates that Option 4 is an attempt to combine insights from probabilistic safety analyses with a deterministic approach. The Option 4 approach has been developed after the publication of SSG-2 and was explained in more detail during the IAEA Division of Nuclear Installation Safety (NSNI) Seminar titled “Assessing Safety Margins and Avoiding Cliff-Edge Effects at NPPs by Applying Option 4 from SSG-2” held on 14 May 2013.

Objective & Conclusions

The NSNI Seminar, presented by Milorad Dusic of the IAEA’s Safety Assessment Section at IAEA Headquarters, focused on the main elements of how to perform Option 4 of the SSG-2. The general conclusions of the seminar included the following: the conservative approach is still used for licensing purposes in most countries; some countries allow BEPU approach in licensing; Option 4 will remain a “research option” for quite some time; and the combined insights from DSA and PSA will continue to be explored. The presentation was followed by a stimulating discussion among colleagues from NSNI. For more information on the Seminar, please send an email to the GSAN Contact Point.