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IAEA SSG-27 - Criticality Safety in the Handling of Fissile Material

ARPANSA coordinates comments on behalf of Australia on IAEA draft documents. We provide feedback to the IAEA through Safety Standards Committee members.

ARPANSA requests comments on drafts in relation to:

  • Relevance and usefulness. Are the stated objectives appropriate, and are they met by the document?
  • Scope and completeness. Is the stated scope appropriate and adequate to cover the document?
  • Quality and clarity. Do the requirements/guidance represent the current consensus among specialists in the field? Are they expressed in a clear and coherent way?

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The Issue
Start/End Date: 
Tuesday 21 April 2020 - 11:00 to Friday 15 May 2020 - 17:00

What is the guide used for?

The purpose of SSG-27 is to provide recommendations on how to meet the specific safety requirements for ensuring subcriticality when dealing with fissile material in the handling, processing, storage, transport and disposal of these materials and for planning the response to criticality accidents. 

ARPANSA uses the guide for assessment of new applications to licence nuclear installations and applications to make relevant changes . The guidelines are incorporated into the ARPANSA performance objectives and criteria which are applied during facility inspections.

Justification of revision

The revision of SSG-27 will take into consideration the following: 

  • the new and modified requirements in SSR-4 regarding criticality safety and the revision of the General Safety Requirements along with developments in other IAEA Safety Standards
  • structure of the IAEA Safety Standards
  • feedback from users of the IAEA Safety Standards related to nuclear criticality safety
  • lessons from the accident at the Fukushima Daiichi nuclear power plant and other events in the nuclear industry including those at nuclear fuel cycle facilities
  • operational experience gained from safety evaluation of fuel cycle facilities.

More specifically, amendments of the guide are needed to address the following:

  1. Update to references.
  2. As mentioned above there are several new requirements in SSR-4 and other requirements have been substantively modified compared to their original form in NS-R-5 Safety of Nuclear Fuel Cycle Facilities. These requirements are not fully addressed in the guide, particularly Req. 21 Design extension conditions, Req.27 Human factors engineering, Req. 38 Design for criticality safety, Req. 66 Criticality control in operation and Req. 75 Interfaces between safety, nuclear security and the state system of accounting for and control of nuclear material which all relate to criticality safety.
  3. The content of the guide will be checked against Appendices and Annexes of NS-R-5 that were removed when replaced by SSR-4.
  4. Some statements in the guide that are expressed as “should” statements may now duplicate some requirements of SSR-4. Such statements should be carefully checked and either removed or modified to make them useful recommendations, supporting the appropriate requirements.
  5. In some cases, the IAEA Safety Guides have been developed to support the GSRs (e.g. SSG-41 for predisposal management of radioactive waste). These safety guides should be referenced where appropriate, along with other safety series documents that are relevant.
  6. In some places, the guide should be updated to better reflect the current operational practices at nuclear fuel cycle facilities and relevant state-of-the-art.
  7. Analyses of operating experience and safety culture in ageing nuclear fuel cycle facilities worldwide indicate that some guidance needs to be strengthened to support Member States in enhancing criticality safety in this regard.
  8. Consider interfaces between all the SSGs for nuclear fuel cycle facilities; the revised guide should be compatible and consistent with other related SSGs.
  9. Application of the graded approach to the criticality safety issues should be explained.
  10. Relevant feedback from operational experience will be considered when revising the guide.

Main revisions to the guide 

Section Main revisions

Standardize background, objective and scope. The background, objective and scope need to be clearly specified. 

Update references.


Check consistency and adequacy with SSR-4. 

Include information to clarify: 

  • safety criteria and acceptance criteria; 
  • prevention and mitigation design features and operational control; 
  • the interface between safety, nuclear security and the State system of accounting for, and control of, nuclear material. 
  • Align discussion of graded approach with SSR-4 regarding the nuclear criticality safety 

Check consistency and adequacy with SSR-4. 

The following should be made consistent with SSR-4: terminology introduced by SSR-4 (credible abnormal conditions, conditions included in the design); the definition of concept of defence in depth; the definition of safety functions; safety classification; operational limits and conditions, design extension conditions; classification and qualification of items important to safety. 

SSR-4, Requirements 38 and 66 on design for criticality safety and criticality control in operation should be addressed fully including: 

  • Para 6.139 of SSR-4 related to methods for ensuring criticality safety
  • Para 6.144 of SSR-4 related to important factors for criticality (including temperature). 

Include information to clarify: 

  • application of conservative approach
  • definition and application of double contingency principle
  • application of inherent safety principle
  • means of mitigation of a criticality accident. 

Add guidance on the implementation of following requirements in relation to criticality safety: 

  • operational limits and conditions
  • structures, systems and components important to criticality safety 
  • maintenance, periodic testing and inspection
  • ageing management 
  • training of personal
  • supervision
  • records and operational documentation
  • accountancy (material control)
  • firefighting
  • warning notices. 

Update references.



Check consistency and adequacy with SSR-4. 

Include information to clarify: 

  • application of design extension conditions to criticality safety assessment
  • using Criticality Safety Benchmark. 

The guidance on means of measurements and evaluation of associated uncertainties should be made consistent with SSR-4. 

Update references.


Check consistency and adequacy with SSR-4. 

Make SSG-27 the basic document for the criticality control programme with other SSG’s addressing specific criticality issues. 

Consider additional guidance where appropriate on the following for each practice: 

  • handling
  • storage arrangements
  • training of personnel
  • moderation control
  • loading and unloading packages intended for transport. 

Expand subsection related to uranium enrichment and conversion facilities and add clarification on implementation of para 9.88b of SSR-4 on preventing criticality during the cleaning of equipment and cylinders. 

Update references.


Check consistency and adequacy with SSR-4. 

Consider additional guidance on false alarm of criticality detection and alarm systems. 

Update references.

Annex Update list of relevant international standards

How to make a comment

ARPANSA will compile all comments prior to providing the national input to the IAEA. Please use the comment template provided to have your say. You may use the online webform available below or submit the form via e-mail to stakeholdercommentatarpansa.gov.au

Comments will be accepted until 15 May 2020. 

View draft documents on the IAEA website:

Download draft template for comments:


21 Apr 2020 - 11:00
15 May 2020 - 17:00
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