Safety Design Criteria Task Force (SDCTF) - Concluded

The GIF Policy Group established the safety and reliability goals for Generation-IV Nuclear Energy Systems in 2002 in a publication titled “Generation-IV Nuclear Energy Systems under the GIF Roadmap” and the GIF Risk & Safety Working Group proposed the “Basis for safety approach for design & assessment of Generation-IV Nuclear Systems”. In addition, the SFR System Steering Committee set the design goals for the SFR systems in 2007 in the publication “SFR System Research Plan”. It is recognized that domestic codes and standards will be used when developing the detailed designs of structures, systems and components. However, there is a large gap between the high-level safety fundamentals and the detailed codes and standards.

The idea to establish “Safety Design Criteria (SDC)” to fill that gap for one of the selected Generation-IV reactor systems was proposed and discussed at the  GIF Policy Group meeting in October 2010. It was recognised that such SDC would fill the middle level of the safety standard hierarchy and would be essential to achieve the enhanced safety goals of Generation-IV reactor systems. It was decided to start with the GIF Sodium-cooled Fast Reactor (SFR) systems and the “GIF Task Force on Safety Design Criteria” (SDC-TF) was set up to draft a specific SDC for SFR.

After the completion of SDC, there were some incentives and needs for making “further technical specification of the criteria specific to Gen-IV SFRs” - “to utilize the SDC as the starting reference for safety standardization” and also “to understand/explain the SFR specific safety features & technology in comparison with LWR systems” for discussions within international organizations where regulatory bodies participate (e.g. IAEA).  The 2^nd phase of SDC-TF was set up to develop 2 types of Safety Design Guidelines (SDGs).

The SDC-TF has produced the SFR safety documents listed below and successfully completed most of its missions.

• Safety Design Criteria for Generation IV Sodium-cooled Fast Reactor System
• Safety Design Guidelines on Safety Approach and Design Conditions for Generation IV Sodium-cooled Fast Reactor Systems
• Safety Design Guidelines on Structures, Systems and Components for Generation IV Sodium-cooled Fast Reactor Systems

To discuss remaining topics, SDC-TF members proposed to the GIF PG that the SDC TF joins the Risk and Safety WG (RSWG) on the GIF PG meeting(Oct. 2019, Weihai, China), and the PG approved it. The SDC-TF members joined the RSWG from the RSWG meeting in June 2020.

The SDC-TF completed the SFR Safety Design Criteria (SDC) report in 2013 as the outcome of its phase I activities, distributed it to international organisations—IAEA, MDEP, NEA/CNRA, and regulatory bodies of the GIF member states with active SFR development programmes, namely, China, Euratom, France, Japan, Korea, Russia and the United States—and revised it on the basis of their comments. In the revision process , the SDC-TF adopted many technical descriptions of the IAEA SSR 2/1 revision 1 issued in 2016, including new provisions that reflect lessons learnt from the TEPCO’s Fukushima Daiichi nuclear power plants accident. It published the revised SFR SDC report in 2017 after the approval of the GIF Experts Group (EG) and Policy Group (PG)..

The contents of the SDC are grouped into the following four parts:

1. Introduction and Safety approach to the SFR as a Generation-IV reactor system (Chapters 1 and 2)
2. Criteria for the overall safety design and specific structure, system and component design (Chapters 3 to 6)
3. A Glossary, covering specific terminologies for the SFR system and for Generation IV reactor systems in general.
4. Appendices.

The purpose of the SSC SDG is to guide and support SFR designers when practically applying the SDC in design process so that their design can ensure the highest level of safety. The SSC SDG builds bridges between the recommendations of the SA SDG and each SSC design. In addition, the SSC SDG describes recommendations to meet the requirements of the SDC Report which are not covered in the SA SDG. The recommendations in the SSC SDG include measures considering SFR’s reactivity characteristics against anticipated transient without scram (ATWS), and the measures to practically eliminate the core uncovering and the complete loss of decay heat removal function. The recommendations which are not covered in the SA SDG are on fuels and materials under high temperature, radiation conditions and on measures against various hazards such as sodium fire, sodium-water reaction, and load factors on the containment system, for example.

The SSC SDG describes the three fundamental safety systems: the core system, the coolant system, and the containment system, which particularly includes selected 14 focal points regarding the SFR-specific safety features as listed in the table below. The SDC-TF referred to design features of Generation IV SFR systems, and the descriptions, definitions, and formats of IAEA NS-G series to develop the recommendations. Although the current SSC SDG primarily covers the main components, it will also address other SSCs such as fuel handling and fuel storage systems. The SDC-TF distributed the SSC SDG in 2019 to OECD/NEA WGSAR and IAEA Department of Nuclear Energy to receive external review.