Direct predecessors of this report are: IAEA-TECDOC-1485, entitled Status of Innovative Small and Medium Sized Reactor Designs 2005: Reactors with Conventional Refuelling Schemes [2], published in March 2006, and IAEA-TECDOC-1536, Status of Innovative Small Reactor Designs Without On-Site Refuelling [3], published in January 2007. These reports presented the design and technology development status and design descriptions for concepts of innovative SMRs developed worldwide. Design descriptions of SMRs in these reports incorporated descriptions of safety concepts prepared according to a common outline. However, these descriptions were rather limited in detail because of limited space in the reports, which were also dedicated to the presentation of other aspects of innovative SMRs, including descriptions of design, economics, proliferation resistance and security, fuel cycle options, and innovative infrastructure provisions. More importantly, descriptions of SMR safety design concepts in these reports were not always structured according IAEA safety standard recommendations, specifically regarding defence in depth strategies

Another predecessor of this report is IAEA-TECDOC-1487, Advanced Nuclear Plant Design Options to Cope with External Events [5, 6], published in February 2006, which provided structured descriptions and explanations of the design features of 14 advanced nuclear power plants incorporating protection against the impacts of natural and human induced external events. The designs considered in that report included several SMRs.

The present report, therefore, provides an in-depth description of safety design features used to achieve defence in depth in 11 innovative SMR concepts selected to represent all major reactor lines with near to medium and longer term deployment potential. These descriptions are structured to follow the definitions and recommendations of IAEA safety standard NS-R-1, Safety of the Nuclear Power Plants: Design Requirements [7] and include some references to other IAEA safety guides and documents, including NS-G-3.3, Evaluation of Seismic Hazard for Nuclear Power Plants [8], and NS-G-1.5, External Events Excluding Earthquakes in the Design of Nuclear Power Plants [9], as well as recommendations by the International Nuclear Safety Advisory Group [10 11], and non-consensus definitions suggested in IAEA publications [5, 12]. The basic definitions recommended or suggested in the above mentioned IAEA publications are reproduced in Appendix 2 of this report.

In September 2007, the IAEA published IAEA-TECDOC-1570, Proposal for a Technology-Neutral Safety Approach for New Reactor Designs [13]. Based on a critical review of IAEA safety standard NS-R-1,

Safety of the Nuclear Power Plants: Design Requirements [7], IAEA-TECDOC-1570 outlines a methodology/ process to develop a new framework for the safety approach based on quantitative safety goals (a probability — consequences curve correlated with each level of defence in depth), fundamental safety functions, and generalized defence in depth, which includes probabilistic considerations. Further elaboration of IAEA safety standards suggested in reference [13] could facilitate expansion of design development and safety qualifications of several medium and longer term SMRs addressed in the present report, thus recommendations in this publication are referenced in Section 3, which highlights design features of selected SMRs. Limited information provided by Member States for this report made it impossible to consider in full the recommendations of IAEA safety standards and guides. Where possible, references to other recently published IAEA reports are included, when such recommendations may be considered in more detail; see Ref. [6].