As it was mentioned in Section 9.3, the current deterministic approach can be used to justify the reduced off-site emergency planning requirements for advanced reactors, including SMRs, in countries where the provisions for such a justification exist. However, the deterministic justification is likely to be conservative as the assumptions typically used in it are conservative.

A risk-informed approach defines the acceptance criteria based on a “probability — consequences” curve derived from the Level 3 probabilistic safety analysis (PSA), which makes it possible to take into account the smaller source terms offered by some advanced SMRs [9.14, 9.17]. Risk-informed regulations are being developed in several countries, including the United States and the Republic of Korea, and risk-informed safety standards are being developed by the IAEA [9.17]. At least one country, Argentina, already has a risk-informed approach incorporated in its national regulations for NPP licensing, see annex III in reference [9.14].

In 2007, the IAEA has published the IAEA-TECDOC-1570 Proposal of a Technology — Neutral Safety Approach for New Reactor Designs [9.17]. This publication suggests “.a methodology/process to develop a new framework for development of the safety approach based on quantitative safety goals[76], fundamental safety functions, and generalised defence-in-depth, which includes probabilistic considerations.” However, publication [9.17] is not an IAEA Safety Standard.

In the United States, the US NRC considers developing a set of performance based, risk — informed, and technology-neutral requirements for licensing of the power reactors, to be included in the NRC regulations as a new 10 CFR Part 53 that could be used as an alternative to the existing requirements 10 CFR Part 50 [9.15]. The 10 CFR Part 53 would provide a set of risk-informed requirements for both light water and non light water reactor designs [9.14]. A risk-informed regulation implementation plan (RIRIP) was adopted by the US NRC in 2006 [9.18], but the overall progress toward 10 CFR Part 53 is rather slow, and this part of the regulations is currently indicated as ‘reserved’ on the US NRC Web-site [9.19].

Once established, risk-informed national regulations could help the designers of advanced SMRs justify the reduced off-site emergency planning requirements for their designs. To achieve this, a method to quantify the reliability of passive safety systems would need to be established, as discussed in Section 9.3.

References

[9.1] United States Nuclear Regulatory Commission (US NRC), Office of Nuclear Reactors — Advanced Reactors: www. nrc. gov/reactors/advanced/pbmr. html

[9.2] United States Nuclear Regulatory Commission (US-NRC), Office of Nuclear Reactors — Advanced Reactors: www. nrc. gov/reactors/advanced/hyperion. html

[9.3] IAEA (2009), Passive Safety Systems and Natural Circulation in Water Cooled Nuclear Power Plants, IAEA-TECDOC-1624 Vienna, Austria.

[9.4] Marques M., et al (2005), “Methodology for the reliability evaluation of a passive system and its integration into a Probabilistic Safety Assessment”, Nuclear Engineering and Design 235, pp 2612-2631.

[9.5] Nayak, A. K., M. R. Gartia, A. Anthony, G. Vinod, A. Srivastav and R. K. Sinha (2007), “Reliability Analysis of a Boiling Two-phase Natural Circulation System Using the APSRA Methodology”, Proceedings of International Congress on Advances in Nuclear Power Plants (ICAPP 2007), Nice, France, May 13-18, 2007 (Paper no. 7074).

[9.6] IAEA (2010), Small Reactors without On-site Refuelling: General Vision, Neutronic Characteristics, Emergency Planning Considerations, and Deployment Scenarios, Final Report of IAEA Coordinated Research Project on Small Reactors without On-site Refuelling, IAEA — TECDOC-1652, Vienna, Austria.

[9.7] Web-page of the IAEA Coordinated Research Project “Development of Methodologies for the Assessment of Passive Safety System Performance in Advanced Reactors”: www. iaea. org/NuclearPower/Downloads/SMR/CRPI31018/CRP_Programme. pdf

[9.8] IAEA (2000), Safety of the Nuclear Power Plants: Design Requirements, Safety Standards Series, No. NS-R-1, IAEA, Vienna, Austria.

[9.9] IAEA (1999), ‘Basic Safety Principles for Nuclear Power Plants’: 75-INSAG-3 rev. 1 / INSAG-12, Vienna, Austria.

[9.10] IAEA (2005), “Innovative Small and Medium Sized Reactors: Design Features, Safety Approaches and R&D Trends”, Final report of a technical meeting held in Vienna, 7-11 June 2004, IAEA-TECDOC-1451, Vienna, Austria.

[9.11] IAEA (2006), Status of Innovative Small and Medium Sized Reactor Designs 2005: Reactors with Conventional Refuelling Schemes, IAEA-TECDOC-1485 Vienna, Austria.

[9.12] IAEA (2006), Advanced Nuclear Plant Design Options to Cope with External Events, IAEA- TECDOC-1487, Vienna, Austria.

[9.13] IAEA (2010), Small Reactors without On-site Refuelling: General Vision, Neutronic Characteristics, Emergency Planning Considerations, and Deployment Scenarios, Final Report of IAEA Coordinated Research Project on Small Reactors without On-site Refuelling, IAEA — TECDOC-1652, Vienna, Austria.

[9.14] IAEA (2009), Design Features to Achieve Defence in Depth in Small and Medium Sized Reactors, IAEA Nuclear Energy Series Report NP-T-2.2, Vienna, Austria.

[9.15] U. S. Nuclear Regulatory Commission (2005), “Backgrounder on Nuclear Power Plant Licensing Process”:

www. nrc. gov/reading-rm/doc-collections/fact-sheets/licensing-process-bg. html

[9.16] IAEA (2007), Status of Small Reactor Designs without On-site Refuelling, IAEA-TECDOC — 1536, Vienna, Austria.

[9.17] IAEA (2007), Proposal for a Technology-Neutral Safety Approach for New reactor Designs, IAEA-TECDOC-1570, Vienna, Austria.

[9.18] U. S. Nuclear Regulatory Commission (2007), “History of the NRC’s Risk-Informed Regulatory Programs”: www. nrc. gov/about-nrc/regulatory/risk-informed/history. html

[9.19] U. S. Nuclear Regulatory Commission (2010), “NRC Regulations Title 10, Code of Federal Regulations”: www. nrc. gov/reading-rm/doc-collections/cfr/