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    Assessment of Defence in Depth for Nuclear Power Plants
    Assessment of Defence in Depth for Nuclear Power Plants
    Assessment of Defence in Depth for Nuclear Power Plants
    Ebook170 pages1 hourSafety Reports Series

    Assessment of Defence in Depth for Nuclear Power Plants

    By IAEA

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    This publication describes the updated version of the method for the assessment of comprehensiveness of defence in depth and demonstrates the overall improvement in assessment results when using it. For assessment of comprehensiveness, five levels of defence in depth are considered. To ensure that safety objectives are met at each level of defence in depth, the integrity of relevant fission product barriers is maintained by the safety functions. A set of challenges to the performance of safety functions and the mechanisms leading to the challenges are specified by the method. Finally, a comprehensive list of safety provisions, which contribute to preventing these mechanisms from occurring, is specified. These provisions encompass the inherent safety features, equipment, procedures, personnel availability, personnel training and safety culture aspects. The challenges, mechanisms and provisions for all levels of defence in depth are presented in the assessment method in the form of objective trees.
    LanguageEnglish
    PublisherInternational Atomic Energy Agency
    Release dateJun 24, 2024
    ISBN9789201451231
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      Book preview

      Assessment of Defence in Depth for Nuclear Power Plants - IAEA

      1.png

      Assessment of

      Defence in Depth for

      Nuclear Power Plants

      SAFETY REPORTS SERIES No. 46 (Rev. 1)

      Assessment of

      Defence in Depth for

      Nuclear Power Plants

      INTERNATIONAL ATOMIC ENERGY AGENCY

      VIENNA, 2024

      COPYRIGHT NOTICE

      All IAEA scientific and technical publications are protected by the terms of the Universal Copyright Convention as adopted in 1952 (Geneva) and as revised in 1971 (Paris). The copyright has since been extended by the World Intellectual Property Organization (Geneva) to include electronic and virtual intellectual property. Permission may be required to use whole or parts of texts contained in IAEA publications in printed or electronic form. Please see

      www.iaea.org/publications/rights-and-permissions for more details. Enquiries may be addressed to:

      Publishing Section

      International Atomic Energy Agency

      Vienna International Centre

      PO Box 100

      1400 Vienna, Austria

      tel.: +43 1 2600 22529 or 22530

      email: [email protected]

      www.iaea.org/publications

      © IAEA, 2024

      Printed by the IAEA in Austria

      June 2024

      STI/PUB/2008

      https://doi.org/10.61092/iaea.dbwn-89a9

      IAEA Library Cataloguing in Publication Data

      Names: International Atomic Energy Agency.

      Title: Assessment of defence in depth for nuclear power plants / International Atomic Energy Agency.

      Description: Vienna : International Atomic Energy Agency, 2024. | Series: safety reports series, ISSN 1020–6450 ; no. 46 (Rev.1) | Includes bibliographical references.

      Identifiers: IAEAL 23-01623 | ISBN 978–92–0–144923–8 (paperback : alk. paper) | ISBN 978–92–0–145023–4 (pdf) | ISBN 978–92–0–145123–1 (epub)

      Subjects: LCSH: Nuclear power plants — Safety measures. | Nuclear reactors — Safety measures. | Nuclear power plants — Design and construction.

      Classification: UDC 621.039.58 | STI/PUB/2008

      FOREWORD

      The concept of defence in depth has evolved from the original idea of using multiple physical barriers against releases of radioactive materials to incorporating a combination of barriers and complementary means of providing the barriers with consecutive and independent levels of protection. Defence in depth is an overall safety philosophy that encompasses the entire lifetime of a nuclear power plant (NPP), including siting, design, manufacture, construction, commissioning, operation and decommissioning. Defence in depth is applied by means of organizational, behavioural or design related safety measures, and it represents a focal point for the IAEA’s safety related activities.

      In the late 1990s, the IAEA recognized a need for more specific guidance on the implementation and assessment of defence in depth in NPPs. To address this need, in 2005 the IAEA published Safety Reports Series No. 46, Assessment of Defence in Depth for Nuclear Power Plants. The Safety Report introduced an assessment method (objective trees) that was designed to facilitate the assessment of an NPP’s conformance to the concept of defence in depth and was primarily applicable to existing NPPs. Since its publication, the method described in the Safety Report has been used in a number of practical applications.

      The present publication is a revision of Safety Reports Series No. 46 that takes into account developments since the publication of the original Safety Report, including significant enhancements of the international safety requirements for NPPs. It also incorporates operating experience and lessons learned from previous applications of the method.

      The publication describes the updated version of the original method for assessing the comprehensiveness of defence in depth and demonstrates the overall improvement in assessment results when it is used. For assessment of comprehensiveness, five levels of defence in depth are considered. To ensure that safety objectives are met at each level of defence in depth, the integrity of relevant fission product barriers is fulfilled by the safety functions. A set of challenges to the performance of safety functions and the mechanisms leading to these challenges are specified by the method. Finally, a comprehensive list of safety provisions, which contribute to preventing these mechanisms from occurring, is specified. These provisions encompass the inherent safety features, equipment, procedures, personnel availability, personnel training and safety culture aspects. The challenges, mechanisms and provisions for all levels of defence in depth are presented in the assessment method in the form of objective trees.

      The assessment method is intended to be used predominantly by the operating organization, and thus covers the responsibility of the operating organization for all stages of the NPP’s lifetime, from siting to the cessation of operation, as well as external factors important to safety that can be influenced by the operating organization. Nevertheless, the method provides useful practical guidance for any other user requiring a comprehensive assessment of defence in depth, including regulatory bodies and technical support organizations providing services either to the regulatory body or to the operating organization.

      The on line supplementary file for this publication, which can be found on the publication’s individual web page at https://doi.org/10.61092/iaea.dbwn-89a9, provides a full set of objective trees for the purpose of practical assessment of the defence in depth capabilities of NPPs.

      The IAEA is grateful to the experts from ČEZ and the Japan Nuclear Safety Institute who contributed to this publication. The IAEA officers responsible for this publication were A. Duchac and and J. Luis Hernández of the Division of Nuclear Installation Safety.

      EDITORIAL NOTE

      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.

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

      Guidance and recommendations provided here in relation to identified good practices represent expert opinion but are not made on the basis of a consensus of all Member States.

      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.

      The IAEA has no responsibility for the persistence or accuracy of URLs for external or third party Internet web sites referred to in this book and does not guarantee that any content on such web sites is, or will remain, accurate or appropriate.

      The authoritative versions of the publications are the hard copies issued and available as PDFs on www.iaea.org/publications.To create the versions for e-readers, certain changes have been made, including the movement of some figures and tables.

      CONTENTS

      1. INTRODUCTION

      1.1. Background

      1.2. Objective

      1.3. Scope

      1.4. Structure

      2. THE CONCEPT OF DEFENCE IN DEPTH

      2.1. General considerations

      2.2. Fulfilment of the fundamental safety functions

      2.3. Practical elimination

      3. APPROACH TO TAKING INVENTORY OF THE DEFENCE IN DEPTH CAPABILITIES OF A PLANT

      3.1. Defence in depth and accident management

      3.2. Description of the assessment approach

      3.3. Specifications of the provisions

      3.4. Objective trees

      4. USE OF THE METHOD

      5. POTENTIAL APPLICATIONS

      Appendix I: FUNDAMENTAL SAFETY FUNCTIONS AND SAFETY FUNCTIONS

      Appendix II: CONTENT OF THE ONLINE SUPPLEMENTARY FILE

      REFERENCES

      Annex I: APPROACH TO DEMONSTRATION OF PRACTICAL ELIMINATION OF PLANT EVENT SEQUENCES LEADING TO EARLY OR LARGE RADIOACTIVE RELEASES

      Annex II: EXPLANATION AND JUSTIFICATION OF MODIFICATIONS OF OBJECTIVE TREES

      DEFINITIONS

      ABBREVIATIONS

      CONTRIBUTORS TO DRAFTING AND REVIEW

      1. INTRODUCTION

      1.1. Background

      The primary means of preventing accidents in a nuclear power plant (NPP) and mitigating the consequences of accidents if they do occur is the application of the concept of defence in depth. Defence in depth is defined in the IAEA Nuclear Safety and Security Glossary [1] as:

      "A hierarchical deployment of different levels of diverse equipment and procedures to prevent the escalation of anticipated operational occurrences and to maintain the effectiveness of physical barriers placed between a radiation source or radioactive material and workers, members of the public or the

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