This report is intended for different categories of stakeholders, including designers and potential users of innovative SMRs, as well as officers in ministries of atomic energy commissions in Member States responsible for implementing nuclear power development programmes or evaluating nuclear power deployment options in the near, medium, and longer term.

The overall objectives of this report are:

(1) To assist developers of innovative SMRs in defining consistent defence in depth approaches regarding the elimination of accident initiators/ prevention of accident consequences through design and the incorporation of inherent and passive safety features and passive systems in safety design concepts of such reactors;

(2) To assist potential users of innovative SMRs in their evaluation of the overall technical potential of SMRs with inherent and passive safety design features, including their possible implications in areas other than safety.

The specific objectives of this report are:

— To present the state of the art in design approaches used to achieve defence in depth in pressurized water reactors, pressurized light water cooled heavy water moderated reactors, high temperature gas cooled reactors, sodium cooled and lead cooled fast reactors, and non-conventional designs within the SMR range;

— To highlight benefits and negative impacts in areas other than safety arising from the implementation of inherent and passive safety design features;

— To identify issues of performance reliability assessment for passive safety systems in advanced reactors, and to highlight further research and development needs arising therefrom.

Designers of SMRs not considered in the present report (currently a minimum of 45 innovative SMR concepts and designs are being analysed or developed worldwide [2, 3]) could benefit from the information published here, which is structured to follow the definitions and recommendations established in IAEA safety standards or suggested in other IAEA publications. It should be noted that IAEA safety standards are used as the base for national nuclear regulations in many developing countries, and that this trend will likely continue into the future.

The information presented in this report could be used in assessment studies for innovative nuclear energy systems (INSs) involving SMRs, as conducted by the IAEA’s International Project on Innovative Reactors and Nuclear Fuel Cycles (INPRO) [14].

Part of this report is elaborated upon through participation of research teams in Member States involved in the development of methodologies for reliability assessments of passive safety systems in advanced reactors. This part (see Appendix I) provides justification for the coordinated research project on Development of Methodologies for the Assessment of Passive Safety System Performance in Advanced Reactors, which is being implemented by the IAEA in its programme during the 2008-2009 budget cycle.