There is a continued interest among Member States in the development and application of small and medium sized reactors (SMRs). In the very near term, most new nuclear power plants (NPPs) are likely to be evolutionary water cooled reactor designs building on proven systems while incorporating technological advances and often economies of scale, resulting in outputs of up to 1600 MW(e) from the reactor. For the longer term, the focus is on innovative designs to provide increased benefits in the areas of safety and security, non­proliferation, waste management, resource utilization and economics, as well as to offer a variety of energy products and flexibility in design, siting and fuel cycle options. Many innovative designs are implemented in reactors within the small to medium size range having equivalent electric power of less than 700 MW(e) or even less than 300 MW(e).

Incorporation of inherent and passive safety design features has become a ‘trademark’ of many advanced reactor concepts, including several evolutionary designs and nearly all innovative SMR design concepts. Ensuring adequate defence in depth is important for reactors with smaller output because many of them are being designed to allow greater proximity to the user, specifically when non-electrical energy products are targeted.

The IAEA provides a forum for the exchange of information by experts and policy makers from industrialized and developing countries on the technical, economic, environmental, and social aspects of SMR development and implementation. It makes this information available to all interested Member States by producing status reports and other publications focusing on advances in SMR design and technology development.

The objective of this report is to assist developers of SMRs in Member States in defining consistent defence in depth approaches regarding the elimination of accident initiators/prevention of accident consequences through design and incorporation of inherent and passive safety features and passive systems into safety design concepts of such reactors. Another objective is to assist potential users in Member States in their evaluation of the overall technical potential of SMRs with inherent and passive safety design features, including possible implications in areas other than safety.

This report is intended for different categories of stakeholders, including designers and potential users of innovative SMRs, as well as officers in ministries or 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 main sections of this report present state of the art advances in defence in depth approaches based on the incorporation of inherent and passive safety features into the design concepts of 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 within the SMR range. They also highlight benefits and negative impacts in areas other than safety arising from the incorporation of such features.

The annexes provide descriptions of the design features of 11 representative SMR concepts used to achieve defence in depth and patterned along a common format reflecting the definitions and recommendations of the IAEA safety standards. The annexes were prepared by designers of the corresponding SMRs.

The IAEA officer responsible for this publication was V. Kuznetsov of the Division of Nuclear Power.

EDITORIAL NOTE

This report has been edited by the editorial staff of the IAEA to the extent necessary for the reader’s assistance.

This report does not address questions of responsibility, legal or otherwise, for acts or omissions on the part of any person.

Although great care has been taken to maintain the accuracy of information contained in this publication, neither the IAEA nor its Member States assume any responsibility for consequences which may arise from its use.

The use of particular designations of countries or territories does not imply any judgement by the publisher, the IAEA, as to the legal status of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries.

The mention of names of specific companies or products (whether or not indicated as registered) does not imply any intention to infringe proprietary rights, nor should it be construed as an endorsement or recommendation on the part of the IAEA.