Realistic methods for calculating the releases and consequences of a large LOCA

European Commission Directorate-General For The Information Society And Media Directorate-General For Research And Innovation

Description

Second seminar on practical decommissioning experience with nuclear installation in the European Community: Sellafield, Windermere, 25 and 26 September 1991
Energy research

Informations

• Publié par: EUROPEAN-COMMISSION-DIRECTORATE-GENERAL-FOR-THE-INFORMATION-SOCIETY-AND-MEDIA-DI
• Nombre de lectures: 168
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

Commission of the European Communities
nuclear science
and technology
Realistic methods for calculating
the releases and consequences
of a large LOCA
Report
EUR 14179 EN Commission of the European Communities
nuclear science
and technology
Realistic methods for calculating
the releases and consequences
of a large LOCA
Second seminar on practical
decommissioning experience with nuclear installations
in the European Community
organized by the Commission of the European Communities,
AEA Decommissioning and Radwaste, Windscale
and BNFL Decommissioning Unit, Sellafieid
Seliafield, Windermere, 25 and 26 September 1991
W. Stephenson, L M. C. Dutton, B. J. Handy, C. Smedley
NNC Limited
Booths Hall, Chelford Road
Knutsford, Cheshire WA16 8QZ
United Kingdom
Contract No ETNU - 0001 /UK
Final report
Publication of this report has been supported by the Dissemination of Scientific and Technical Knowledge Unit,
Directorate-General for Information Technologies and Industries, and Telecommunications,
Commission of the European Communities, Luxembourg
Directorate-General
Science, Research and Development PARI EUROP. Biblioth.
1992 N.C. EUR 14179 E
CI. Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Information Technologies and Industries, and Telecommunications
L-2920 Luxembourg
LEGAL NOTICE
Neither the Commission of the European Communities nor any person
acting on behalf of the Commission is responsible for the use which might
be made of the following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1992
ISBN 92-826-4632-7
© ECSC-EEC-EAEC, Brussels • Luxembourg, 1992
Printed in Luxembourg FOREWORD
The work described in this report was carried out within the
framework of the Working Group 1 on the Safety of Thermal Reactors
of the Commission of the European Communities. It forms the third
phase of a study to derive a realistic calculational route to predict
the consequences of a successfully terminated Large Loss of Coolant
Accident (LOCA) at a Pressurised Water Reactor (PWR).
The first phase was the completion of two benchmark studies in 1988.
It was clear from these studies that there is a wide spectrum of
models and assumptions in use within the European Community and that
the predictions for the resulting radiological consequences cover a
range of several orders of magnitude.
It is important to recognise that such differences should not be
interpreted as differences in the standards of safety applied to
nuclear plants in different countries. That can only be assessed
when all the aspects that are relevant to safety and the approach to
licensing are taken into account.
Subsequently two further studies were carried out which extended the
earlier work by proposing a calculational route which is based on
realistic methods and data. The purpose of the present study is to
develop these calculational routes further and to provide a synthesis
of the earlier work.
ACKNOWLEDGEMENT
The methods and data described in this report are the result of a
collaborative effort by representatives from France, Germany and
Belgium as well as the UK. A major input to the report was the work
carried out by the Commissariat a l'Energie Atoraique at
Fontenay-aux-Roses and the report has benefited from the many
suggestions and information provided by Gesellschaft fur
Reaktorsicherheit, Cologne and Vincotte, Brussels.
Ill METHODS OF CALCULATION OF RELEASES AND CONSEQUENCES
OF A LARGE LOCA. CEC CONTRACT NO ETNU-0001/UK
Contents
Page No.
1 INTRODUCTION 1
2 MAJOR DESIGN FEATURES WHICH MAY AFFECT THE 5
RELEASE
2.1 Hot Leg Injection 5
2.2 Primary Containment Spray System
2.3yt Fan Coolers
2.4 Primary Containment Leak. Rate 6
2.5 Presence/Design Features of a
Secondary Containment
2.6 Filtration Efficiency
2.7 Summary 7
3 GENERAL DESCRIPTION OF THE FAULT SEQUENCE 9
3.1 Break Position 9
3.2 The Safeguard Systems
3.3e Blowdown Phase
3.A The Refill Phase 11
3.5e Re flood Phase
3.6 The Long Term Cooling Phase 1
4 THE CORE INVENTORY2
4.1 Benchmark Calculations 1
4.2 Recommendation3
4.3 Sensitivity Studies4
V Contents (cont'd)
Page No
15 THE FAILED FUEL FRACTION
15 5.1 Benchmark. Calculations
5.2 Rupture due to Strain 15
5.3 Probabilistic Analysis 15
5.4 16 Other Analyses
Burst Criteria 18 5.5
5.6 Stress Corrosion Cracking 18
5.7 Recommendation 18
Research 19 5.8
THE RELEASE FROM FAILED FUEL 21
21 6.1 Benchmark Calculations
The Gap Inventory 21 6.2
21 6.2.1 Stable Fission Gas Release
6.2.2 Short-lived Fission Product 22
Release
6.3 The Release from Fragmented Fuel 26
27 6.4 Total Release from the fuel
6.5 The Release in the Dry Phase 28
6.6 Recommendation 29
THE RELEASE OF ACTIVITY TO THE PRIMARY 31
CONTAINMENT
7.1 Benchmark Calculations 31
7.2 The Phases of the Release 32
7.3 The Form of Fission Products 34
Releases in the 'Dry Phase'
7.3.1 Noble Gases 34
7.3.2 Iodine 34
7.3.3 Caesium 34
7.3.4 Other Elements 34
-VI Contents (cont'd)
Page No.
7.4 The Retention of the Dry Phase Release 35
in the Primary Circuit
7.4.1 Recommendation 35
7.4.2 Sensitivity Studies
7.5 Form of Fission Products Released in 36
the Wet Phase
7.6 Recommendations 37
7.6.1 Dry Phase Release when 3
Injection is only in the Cold
Leg
7.6.2 Dry Phase Release when8
Injection is into both the
Cold and Hot Legs
7.6.3 Wet Phase Release when 3
Injection is only into the
Cold Legs
7.6.4 Wet Phase Release when9
Injection is into both the
Hot and Cold Legs
7.7 Further Work 3
RETENTION IN THE PRIMARY CONTAINMENT 41
8.1 General Phenomena 4
8.2 Benchmark Calculations2
8.3 Aerosol Behaviour
8.3.1 General Phenomena
8.3.2 Removal Processes 43
8.3.3 The Blowdown Aerosol7
8.3.4 The Effect of Agglomeration 48
8.3.5 Recommendations 50
8.3.6 Comparison with Experimental Data 51
8.4 The Behaviour of Iodine3
8.4.1 General Phenomena 5
8.4.2 The Chemistry of Inorganic 5
Iodine
8.4.3 Removal of Inorganic Gaseous 54
Iodine
8.4.4 Modelling of Inorganic 55
Iodine Behaviour
VII -Contents (cont'd)
Page No
8.4.5 The Overall Behaviour of 56
Inorganic Iodine
8.4.6 59 The Formation of Organic
Iodine
8.4.7 The Removal of Organic 61
Iodine
8.4.8 Comparison with the Results 61
Licencing Calculations
Summary of Recommendations for 62
Retention In the Primary Containment
8.6 Research 63
8.6.1 Aerosol Behaviour
8.6.2 Chemistry
THE RELEASE OF RADIOACTIVITY TO ATMOSPHERE 65
9.1 Benchmark Calculations 6
9.1.1 General Features5
9.1.2 Leakage through the Primary 6
and Secondary Containments
9.1.3 They Containment 67
Filtration Systems
9.2 The Retention of Activity in Leakage8
Paths
9.3 Release due to Leakage into the 6
Auxiliary Building
9.3.1 Nature of the Release8
9.3.2 Without Aerosol Formation 68
9.3.3 With Aerosoln9
9.4 Summary of Recommendations 71
9.4.1 Leakage Rates from the
Primary Containment and the
Fractionthat Bypasses the
Secondaryt
9.4.2 Secondary Containment 71
Filtration
9.4.3 Filtration of Direct Leakage 7
9.4.4 Leakage from the Safeguard1
Systems
9.5 Further Work 72
VIII