DS511 - Use of a Graded Approach in the Application of the Safety Requirements for Research Reactors

Status: SSG-22 (Rev. 1)

Veröffentlichung  2023

Revision von SSG-22  (Ex DS351)


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Background Information

The current revision of SSG-22 is timely because it predates SSR-3 and most of the General Safety Requirements publications, and as such, it contains many references to superseded requirements, does not fully address all of the current requirements and does not cover the safety of subcritical assemblies. The revised SSG-22 will cover use of a graded approach in all areas important to the safety of research reactors, including subcritical assemblies. The guidance and recommendations in SSG-22 are applicable to all phases of a research reactor lifecycle, including design, construction, commissioning, operation, utilization and modification, extended shutdown and planning for decommissioning.

The objective of SSG-22 is to provide research reactor operating organizations, regulatory bodies and other organizations involved in the site evaluation, design, construction, operation and planning for decommissioning of research reactors with guidance on using a graded approach when implementing the requirements of SSR-3 and the General Safety Requirements as they apply to research reactors.

The scope of SSG-22 will change during the revision process, because it will be expanded to treat subcritical assemblies explicitly and to address application of a graded approach to interfaces between safety and security for research reactors.

The revision of SSG-22 will benefit from amendments to take into consideration the following:

  • Revisions implemented in the General Safety Requirements, other IAEA Safety Standards and, in particular, the new and modified requirements in SSR-3 since publication of the SSG-22;
  • Long Term Structure of the IAEA Safety Standards;
  • Feedback from the users of the IAEA Safety Standards related to research reactors, including feedback from a Technical Meeting on graded approach held in 2016 and attended by 55 participants from 39 Member States;
  • Use of SSG-22 by organizations involved in the safety of subcritical assemblies, which are now in the scope of SSR-3;
  • Lessons from the accident at the Fukushima Daiichi nuclear power plant and other events in the nuclear industry, including those occurring at research reactors that were reported to the Incident Reporting System for Research Reactors.


More specifically, amendments of SSG-22 are needed to address the following:

1. There are several new requirements in SSR-3 and others have been substantively modified from their original form in NS-R-4. Obviously, some of these requirements are not addressed at all in SSG-22, including Req. 22, Design Extension Conditions; Req. 55, Emergency Response Facilities on the Site; Req. 76, Material Conditions and Housekeeping; and Req. 90, Interfaces between nuclear safety and nuclear security. The guidance related to other requirements in SSR-3 that were substantively modified needs to be rechecked and updated to ensure it provides complete and consistent coverage of SSR-3.

2. The IAEA Safety Standards, related to the safety of research reactors (this include IAEA Safety Standards Series No. SSR-3, Safety of Research Reactors (2016), and eleven Specific Safety Guides), were all published before SSG-22 (except SSG-37) and contain information about applying a graded approach in their respective areas. This information needs to be removed from the other Guides and consolidated in a harmonized manner in the revision to SSG-22.

3. The publication of SSR-3 expanded the scope of the safety requirements for research reactors to include subcritical assemblies. As SSG-22 was published prior to SSR-3, it does not provide explicit guidance about how the safety requirements should be implemented for subcritical assemblies using a graded approach. Given that subcritical assemblies are typically much simpler nuclear installations than critical facilities and research reactors that operate at significant power levels, there are many requirements in SSR-3 that can be graded much differently for subcritical assemblies than for other types of research reactors. Target users will benefit from guidance in this area.