DS498 - External Events Excluding Earthquakes in the Design of Nuclear Installations
Status: STEP 12
Revision von NS-G-1.5
Beteiligte IAEO-Komitees: NUSSC, WASSC
Specific Safety Guide
Overview of DS498
A major revisions are:
- New structure and content of the document, extending the scope from NPP to all nuclear installations,
- Design and qualification methods and means of protection for nuclear installations,
- Implementation of safety requirements (DS484, SSR-2/1, SSR-3 and SSR-4),
- Incorporates the progress in the state of practice and the results of research on the effects of all external events excluding earthquakes.
It provides new or updated guidance on:
- General concept and application of safety criteria to the design of structures, systems and components (SSCs) for protection against external events, load combinations and acceptance criteria,
- Safety analysis for Design Basis External Events (DBEEs) and Beyond Design Basis External Events (BDBEEs),
- Safety Margin,
- Technical recommendations for good engineering practice.
Background Information by Step 3
The document (NS-G-1.5) was first published in 2003. The scope of the safety guide will be extended to all nuclear installations. This safety guide considers design protection measures of nuclear installations against external hazards covered by the existing IAEA Safety Standards.
The current revision (DS 498) was initiated to
- Ensure consistency with applicable requirements for site evaluation and design of nuclear installations (SSR-1/DS484, SSR-2/1, SS-R-3 and SSR-4/DS478)
- Ensure coherency and consistency with other relevant IAEA Safety Standards (e.g. SF-1 and GSRs),
- Incorporate the lessons learned and address challenges highlighted IAEA Report on Fukushima-Daiichi NPP Accident.
The new information in DS498 includes
- Will address hazards induced Common Cause Failures
- Will address design basis for external hazards including combination of hazards
- DEC against external hazards (when applicable)
- Recommendations for achieving adequate safety margins to avoid cliff edge effects consistent with applicable safety requirements.
- The terminology will be made consistent with the new definitions in the safety requirements and the safety glossary
- References will be updated
Fukushima Daiichi Implications
- Importance of adequate design basis
- Appropriate considerations of uncertainties
- Common-cause effects of external events can compromise several layers of defense in depth at the same time
- Combined effects of natural events need to be considered