The report includes an introduction, 6 Sections, 4 appendices and 10 annexes.

The introduction (Section 1) describes the background and identifies the objectives, the scope and the structure of this report, as well as the approach used in its preparation and the design status of the SMRs considered.

Section 2 provides an overview of the considerations for the incorporation of inherent and passive safety features into safety design concepts of SMRs. These considerations, presented in a generic way and for each reactor line separately, were elaborated at the IAEA technical meetings in June 2005 and in October 2006.

Section 3 presents the design approaches applied by the designers to achieve defence in depth in SMRs. Both passive and active safety design features and systems are included to highlight the role of inherent and passive features and show how they may affect the design/function of the active safety systems. This section is based on the information and data provided by the designers of SMRs in Member States and presented, in a
structured form, in Annexes I-X in this report. The common format used to describe passive and active safety design features of SMRs is given in Appendix IV.

Section 3 is structured as follows. First, a common general approach is described. Then a description is provided for each reactor line addressed in the present report, including pressurized water reactors, pressurized light water cooled heavy water moderated reactors, high temperature gas cooled reactors, liquid metal cooled fast reactors, and non-conventional designs. For each reactor line, a short summary of the design features of one or more of the corresponding SMRs presented in the annexes is included, followed by summary tables and discussions of the safety design features contributing to each level of defence in depth. In this, dedicated passive and active safety systems are discussed in more detail in conjunction with defence in depth level 3. After that, summary tables and discussions follow on design basis and beyond design basis events, on acceptance criteria, and on features for plant protection against external event impacts. Each section winds-up with a summary table and a discussion of the measures planned in response to severe accidents.

Section 4 provides a review of the benefits and negative impacts in areas other than safety that in view of the SMR designers arise from incorporation of the corresponding inherent and passive safety design features. The discussion is structured along the reviewed reactor lines, in the same way as in Section 3.

Section 5 summarizes the approaches and considerations applied in the selection of combinations of passive and active safety systems in the considered SMRs.

Section 7 is the conclusion. It is elaborated as an executive summary of the report.

Appendix 1 addresses the issue of performance assessment of passive safety systems by providing a summary of background and experience, a short description of the two methodologies for reliability assessment of passive safety systems, and a recommendation for further research and development based on the outputs of a dedicated IAEA technical meeting on June 2006. This appendix is referenced from Section 5.

Appendix 2 includes a paper on periodic confirmation of passive safety feature effectiveness, contributed by D. C. Wade of the Argonne National Laboratory (ANL), USA. This paper is referenced from Appendix 1.

Appendix 3 includes consensus and non-consensus definitions from the IAEA safety standards and other publications relevant to the subject of this report, and also highlights some non-conventional terms used by Member States.

Appendix 4 gives a common format for description of the design features of SMRs as used in Annexes I-X.

Annexes I-X provide descriptions of the design features of the considered SMRs used to achieve defence in depth. The descriptions were contributed by Member States and are done according to the common outline in Appendix 3. The order of the inputs corresponds to that used in Sections 3 and 4, with pressurized water SMRs going first (Annexes I-V), followed by a pressurized light water cooled heavy water moderated reactor (Annex VI), a high temperature gas cooled reactor (Annex VII), the liquid metal cooled fast-spectrum SMRs (Annexes VIII, IX), and the non-conventional design (Annex X).

Contributors to drafting and review of this report are listed on the last page.