The Chernobyl Accident: Updating of INSAG-1 - Publications

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SAFETY SERIES No. 75-INSAG-7
INSAG-7
The Chernobyl Accident:
in
Updating of INSAG-1
LL
A REPORT BY THE
CO
INTERNATIONAL NUCLEAR SAFETY ADVISORY GROUP
INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1992
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Basic objectives, concepts and principles to ensure safety.
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THE CHERNOBYL ACCIDENT: UPDATING OF INSAG-1
INSAG-7
A report by the International Nuclear Safety Advisory Group
The following States are Members of the International Atomic Energy Agency:
AFGHANISTAN HOLY SEE PANAMA
ALBANIA HUNGARY PARAGUAY
ALGERIA ICELAND PERU
ARGENTINA INDIA PHILIPPINES
AUSTRALIA INDONESIA POLAND
AUSTRIA IRAN, ISLAMIC REPUBLIC OF PORTUGAL
BANGLADESH IRAQ QATAR
BELARUS IRELAND ROMANIA
BELGIUM ISRAEL RUSSIAN FEDERATION
BOLIVIA ITALY SAUDI ARABIA
BRAZIL JAMAICA SENEGAL
BULGARIA JAPAN SIERRA LEONE
CAMBODIA JORDAN SINGAPORE
CAMEROON KENYA SLOVENIA
CANADA KOREA, REPUBLIC OF SOUTH AFRICA
CHILE KUWAIT SPAIN
CHINA LEBANON SRI LANKA
COLOMBIA LIBERIA SUDAN
COSTA RICA LIBYAN ARAB JAMAHIRIYA SWEDEN
COTE D'lVOIRE LIECHTENSTEIN SWITZERLAND
CUBA LUXEMBOURG SYRIAN ARAB REPUBLIC
CYPRUS MADAGASCAR THAILAND
CZECHOSLOVAKIA MALAYSIA TUNISIA
DEMOCRATIC PEOPLE'S MALI TURKEY
REPUBLIC OF KOREA MAURITIUS UGANDA
DENMARK MEXICO UKRAINE
DOMINICAN REPUBLIC MONACO UNITED ARAB EMIRATES
ECUADOR MONGOLIA UNITED KINGDOM OF GREAT
EGYPT MOROCCO BRITAIN AND NORTHERN
EL SALVADOR MYANMAR IRELAND
ESTONIA NAMIBIA UNITED REPUBLIC OF
ETHIOPIA NETHERLANDS TANZANIA
FINLAND NEW ZEALAND UNITED STATES OF AMERICA
FRANCE NICARAGUA URUGUAY
GABON NIGER VENEZUELA
GERMANY NIGERIA VIET NAM
GHANA NORWAY YUGOSLAVIA
GREECE PAKISTAN ZAIRE
GUATEMALA ZAMBIA
HAITI ZIMBABWE
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© IAEA, 1992
Permission to reproduce or translate the information contained in this publication may be
obtained by writing to the International Atomic Energy Agency, Wagramerstrasse 5, P.O. Box 100.
A-1400 Vienna, Austria.
Printed by the IAEA in Austria
November 1992
SAFETY SERIES No. 75-INSAG-7
THE CHERNOBYL ACCIDENT:
UPDATING OF INSAG-1
INSAG-7
A report by the
International Nuclear Safety Advisory Group
INTERNATIONAL ATOMIC ENERGY AGENCY
VIENNA, 1992
The International Nuclear Safety Advisory Group (INSAG) is an advisory
group to the Director General of the International Atomic Energy Agency, whose
main functions are:
(1) To provide a forum for the exchange of information on generic nuclear safety
issues of international significance;
(2) To identify important current nuclear safety issues and to draw conclusions on
the basis of the results of nuclear safety activities within the IAEA and of other
information;
(3) To give advice on nuclear safety issues in which an exchange of information
and/or additional efforts may be required;
(4) To formulate, where possible, commonly shared safety concepts.
THIS SAFETY SERIES IS ALSO PUBLISHED IN
FRENCH, RUSSIAN AND SPANISH
VIC Library Cataloguing in Publication Data
The Chernobyl accident : updating of INSAG-1 : INSAG-7 : a report by the
International Nuclear Safety Advisory Group. — Vienna : International
Atomic Energy Agency, 1992.
p. ; 24 cm. — (Safety series, ISSN 0074-1892 ; 75-INSAG-7)
STI/PUB/913
ISBN 92-0-104692-8
Includes bibliographical references.
1. Chernobyl Nuclear Accident, Chernobyl, Ukraine, 1986. I. Inter-
national Atomic Energy Agency. II. International Nuclear Safety Advisory
Group, n. Series.
VICL 92-00042
FOREWORD
by the Director General
New information that has come to light since the Post-Accident Review Meet-
ing on the Chernobyl Accident (held in Vienna from 25 to 29 August 1986) bears
on general issues of the operational safety of nuclear power plants in the then Union
of Soviet Socialist Republics as well as on specific issues relating to the design of
the Chernobyl type light water cooled, graphite moderated RBMK reactors.
As regards general issues, the new information demonstrates the lack of feed-
back of operating experience and the inadequacy of communication between
designers, engineers, manufacturers, constructors, operators and regulators. These
deficiencies, coupled with a lack of clear lines of responsibility, were critical factors
in the events leading up to the Chernobyl accident. These shortcomings have been
tackled at the national level and some improvements have been made.
Valuable lessons can be learned from incidents and accidents, as was demon-
strated after the accident at Three Mile Island nuclear power plant in the United
States of America in 1979, when far reaching follow-up actions were taken to
minimize the risk of a recurrence and to improve procedures for accident manage-
ment. The accident at Chernobyl demonstrated that the lessons from the Three Mile
Island accident had not been acted upon in the USSR: in particular, the importance
of systematic evaluation of operating experience; the need to strengthen the on-site
technical and management capability, including improved operator training; and the
importance of the man-machine interface.
Specific issues relating to the design of the RBMK reactors were the subject
of intensive studies in the USSR after 1986, and some modifications have since been
made to these reactors and to their operating regimes. More recently, discussions
have been held at the international level on the safety of nuclear power plants with
RBMK reactors. International efforts to assist in the safety assessment of the RBMK
reactors have been intensified in recent months.
Efforts to enhance the safety of RBMK reactors will continue; however, inter-
national assistance can only achieve a fraction of what has to be done at the national
level. In addition, the general issues mentioned earlier require sustained efforts to
upgrade the national nuclear safety regime before a safety culture can be inculcated
at all levels and in all the organizations concerned.
The emergence of the new information prompted the IAEA's International
Nuclear Safety Advisory Group (INSAG) to review its former conclusions about the
causes of the Chernobyl accident of April 1986. The present INSAG-7 report updates
the Summary Report on the Post-Accident Review Meeting on the Chernobyl Acci-
dent (IAEA Safety Series No. 75-INSAG-l), published in September 1986. The con-
clusions formulated in the report will broaden the basis for international
consultations to enhance the safety of RBMK reactors.
With this report, INSAG has made a valuable contribution to the task that lies
ahead.
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.
The use of particular designations of countries or territories does not imply any judge-
ment 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 authors are responsible for having obtained the necessary permission for the IAEA
to reproduce, translate or use material from sources already protected by copyrights.
Material prepared by authors who are in contractual relation with governments is
copy righted by the IAEA, as publisher, only to the extent permitted by the appropriate national
regulations.
CONTENTS
1. INTRODUCTION 1
2. FEATURES OF THE REACTOR 3
2.1. Void coefficient of reactivity 3
2.2. Design of control and safety rods 4
2.3. Speed of insertion of the emergency protection rods 4
2.4. Control of power 4
2.5. Instrumentation indicating the reactivity margin 6
2.6. Size of the reactor core 6
2.7. Capability to alter safety systems, plant trips and alarms 6
2.8. Subcooling of the inlet water 7
2.9. Primary coolant system 7
2.10. Containment 8
3. THE ACCIDENT 10
4. MORE RECENT ANALYSES OF THE FAULT SCENARIO 13
4.1. The scenario 13
4.2. Operating reactivity margin 14
5. VIEWS OF INSAG 16
5.1. Design 16
5.2. Operator actions 17
5.3. Safety framework 20
5.4. Implications of ignoring deficiencies 20
5.5. Importance of competent safety analysis 20
5.6. Deficiencies in the regulatory regime 21
5.7. General remarks on the lack of safety culture 21
5.8. Summary assessment 22
6. CONCLUSIONS ON FACTORS CONTRIBUTORY TO
THE ACCIDENT 23
APPENDIX: MEASURES TO IMPROVE THE SAFETY OF
RBMK PLANTS 27
ANNEX I: REPORT BY A COMMISSION TO THE USSR STATE
COMMITTEE FOR THE SUPERVISION OF
SAFETY IN INDUSTRY AND NUCLEAR POWER 29
1-1. Introduction 29
1-2. Brief description of the design of Chernobyl Unit 4 32
1-3. Violations of safety standards and regulations in the
design of Chernobyl Unit 4 34
1-4. Causes and circumstances of the accident 51
1-5. Conclusions 84
References to Annex I 89
Bibliography to Annex I 93
JlHTepaxypa K npHJiOHcenmo I 95
EH6jiHorpa<}>Hsi K IlpHjioaceHHio I 99
ANNEX II: REPORT BY A WORKING GROUP OF
USSR EXPERTS 101
II-1. Brief description and features of the RBMK-1000
reactor of Chernobyl Unit 4 103
II-2. Latest views on how the Chernobyl accident
occurred and developed 107
II-3. Measures to improve the safety of plants with
RBMK reactors 124
II-4. Conclusions 132
LIST OF ACRONYMS AND SYMBOLS 133
MEMBERS OF THE INTERNATIONAL NUCLEAR SAFETY
ADVISORY GROUP, WORKING GROUP MEMBERS AND
ASSOCIATED EXPERTS 135