IEC TR 61838:2009

Nuclear power plants - Instrumentation and control important to safety - Use of probabilistic safety assessment for the classification of functions

IEC/TR 61838:2009 provides a survey of some of the methods by which probabilistic risk assessment results can be used to establish "risk-based" classification criteria, so as to allow FSEs to be placed within the four categories established within IEC 61226. The safety principles and the usefulness of a risk-based approach to classification are discussed and a description of four different approaches is presented. The main technical changes in this second edition with regard to the previous edition are as follows:
- to update the references and the terminology;
- to take into account the progress done since edition 1.

Centrales nucléaires de puissance - Instrumentation et contrôle-commande importants pour la sûreté - Utilisation des évaluations probabilistes de sûreté pour le classement des fonctions

La CEI/TR 61838:2009 étudie différentes méthodes permettant d'utiliser les résultats des évaluations probabilistes des risques afin d'établir des critères de classement basés sur l'évaluation du risque, dans le but de pouvoir classer les FSE dans les quatre catégories établies par la CEI 61226. Les principes de sûreté et l'utilité d'une approche d'évaluation des risques pour le classement sont discutés et la description de quatre approches différentes est présentée. Les principales modifications techniques de cette seconde édition par rapport à la première édition sont les suivantes:
- mettre à jour les références et la terminologie;
- prendre en compte les progrès réalisés depuis la première édition.

General Information

• Status: Published
• Publication Date: 13-Dec-2009
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 27.120.20 - Nuclear power plants. Safety
• ICS: 35.160 - Microprocessor systems
• Technical Committee: SC 45A - Instrumentation, control and electrical power systems of nuclear facilities
• Drafting Committee: WG 7 - TC 45/SC 45A/WG 7
• Current Stage: PPUB - Publication issued
• Start Date: 15-Feb-2010
• Completion Date: 14-Dec-2009

Relations

• Revises: IEC TR 61838:2001 - Nuclear power plants - Instrumentation and control functions important for safety - Use of probabilistic safety assessment for the classification
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC/TR 61838 ®
Edition 2.0 2009-12
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
colour
inside
Nuclear power plants – Instrumentation and control important to safety – Use of
probabilistic safety assessment for the classification of functions

Centrales nucléaires de puissance – Instrumentation et contrôle-commande
importants pour la sûreté – Utilisation des évaluations probabilistes de sûreté
pour le classement des fonctions

IEC/TR 61838:2009
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IEC/TR 61838 ®
Edition 2.0 2009-12
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
colour
inside
Nuclear power plants – Instrumentation and control important to safety – Use of
probabilistic safety assessment for the classification of functions

Centrales nucléaires de puissance – Instrumentation et contrôle-commande
importants pour la sûreté – Utilisation des évaluations probabilistes de sûreté
pour le classement des fonctions

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XB
CODE PRIX
ICS 27.120.20 ISBN 978-2-88910-575-5
– 2 – TR 61838 © IEC:2009
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.10
2 Normative references .10
3 Terms and definitions .11
4 Abbreviations .14
5 Limitations regarding the use of individual approaches alone .14
5.1 General .14
5.2 Limitations regarding the use of a PSA-related approach alone .14
5.3 Limitations regarding the use of the deterministic role-based approach alone.15
6 Open issues regarding categorisation.16
6.1 General .16
6.2 Why categorize: To determine requirements, or do requirements determine
the category? .16
6.3 To what degree are risk-based and probabilistic methods already used
implicitly? .18
6.4 How precise do PSA results need to be? .18
7 Current practices in some member states.19
7.1 General .19
7.2 Brief summaries .19
7.3 More detailed explanations.20
8 A survey of risk-related techniques of categorisation .23
8.1 General .23
8.2 Approach 1: Time and reactor states based approach .25
8.2.1 Categorisation of FSE during the design phase .25
8.2.2 Impact of safety reviews on categorisation .29
8.3 Approach 2: Quantitative importance based approach .29
8.3.1 General .29
8.3.2 Quantitative assignment criteria.30
8.3.3 Quantitative criteria .30
8.3.4 Category assignment.32
8.3.5 Classification procedure .32
8.3.6 Determination of requirements.33
8.4 Approach 3: Consequence – mitigation based approach.33
8.4.1 History: A dual licensing requirement leading to the probabilistic
approach .33
8.4.2 Current probabilistic targets.33
8.4.3 Classification of safety-related systems .34
8.4.4 Application of design requirements .34
8.4.5 Purpose of categorisation .35
8.4.6 Categorisation principles .35
8.4.7 Categorisation methodology .36
8.5 Approach 4: Combined deterministic-probabilistic approach Bbased on NS-
R-1.37
8.5.1 General .37
8.5.2 Basis for the historical approach.38

TR 61838 © IEC:2009 – 3 –
8.5.3 Plant state basis.38
8.5.4 Defence in depth considerations.40
8.5.5 Basis for classification – Based on IEC 61226 .40
8.5.6 Application of IEC 61226 .41
8.5.7 Safety classification methodology.42
8.5.8 Deterministic criteria for safety function categories.43
8.5.9 Other classification considerations .44
8.5.10 Worked example.45
8.5.11 Conclusion .46
8.6 Approach 5: Application of risk methodologies in U.S.A. nuclear regulation .46
9 Comparison of risk-related categorisation results .48
9.1 CANDU plant stepback function.48
9.1.1 Problem statement .48
9.1.2 Solution using approach 3 .49
9.1.3 Comparisons with other methods.50
9.2 Conclusions arising from the use of various approaches .50
Annex A (informative) The use of PSA: methods and results.52
Annex B (informative) Approach 6: Role-Reliability-Timeframe based approach.55
Bibliography.59

Figure 1 – Historical plant states and allowed releases .38
Figure 2 – Plant states and allowed releases .39
Figure 3 – Reliability requirements for state transition barriers.40
Figure 4 – Categories required to maintain plant states .41
Figure 5 – RISC Categories .47
Figure 6 – Event sequence and layer protection identification .49

Table 1 – Classification of I&C FSE .26
Table 2 – Correspondence between IEC 61226 and INSAG-10 .26
Table 3 – Minimum Requirements by Level of Function.28
Table 4 – Equipment requirements.29
Table 5 – Safety significance .36
Table 6 – Failure impact type.36
Table 7 – Category determination .37
Table 8 – Application of the changes to the safety classification methodology .43
Table B.1 – Prevention .56
Table B.2 – Termination.
...