IEC 61226:2020

Overview

IEC 61226:2020 is an international standard developed by the International Electrotechnical Commission (IEC) that specifies the categorization of functions and classification of instrumentation, control (I&C), and electrical power systems important to safety in nuclear power plants. The standard provides a systematic method to assess the safety significance of plant functions and, based on this assessment, classify the associated systems to define appropriate design criteria. This approach ensures that critical systems meet required levels of functionality, reliability, performance, environmental qualification (including seismic considerations), and quality assurance to uphold nuclear safety standards.

This fourth edition of IEC 61226 includes significant updates to align with the latest International Atomic Energy Agency (IAEA) safety requirements such as SSR 2/1 and SSG 30, extends the scope to cover electrical power systems, and reorganizes detailed requirements into normative annexes pending updates to related standards.

Key Topics

• Categorization of Safety Functions IEC 61226 defines a clear scheme to assign nuclear power plant functions into categories reflecting their importance to safety. This categorization drives the further classification of related I&C and electrical power systems.

• Classification of Systems The standard distinguishes between classes of systems corresponding to the function categories. This classification determines the technical design requirements to satisfy safety objectives.

• Design Criteria for Safety-Important Systems The standard mandates design criteria focusing on:

  • Functionality: Ensuring the system performs the intended safety function.
  • Reliability: High dependability during normal and accident conditions.
  • Performance: Meeting operational specifications under all conditions.
  • Environmental Qualification: Resistance to environmental factors such as seismic events.
  • Quality Assurance: Implementation of rigorous QA processes throughout design and operation.

• Methodology for Categorization and Classification Procedures are described for:

  • Identifying operational occurrences, design basis accidents, and extended design conditions.
  • Assigning safety functions to categories A (highest safety importance), B, or C.
  • Classifying I&C and electrical power systems accordingly.

• Normative Annexes and Examples Detailed normative requirements for I&C systems and examples illustrating typical functions and system classifications enhance practical application.

Applications

IEC 61226:2020 is essential for nuclear plant designers, safety analysts, system engineers, and regulators concerned with nuclear safety and instrumentation systems management. The standard is applied to:

• Safety Function Analysis Identify and classify plant functions critical to safety, establishing safety priorities.

• System Design and Procurement Guide engineering decisions to ensure that I&C and electrical power systems meet stringent safety-related criteria.

• Quality Assurance and Compliance Define requisite QA controls and environmental qualifications required for classified systems.

• Regulatory Frameworks and Audits Align plant safety practices with international nuclear safety standards, supporting compliance verification.

• Risk Management Support Defense in Depth strategies by categorizing and segregating safety functions across multiple independent systems.

Related Standards

Implementation of IEC 61226 should be coordinated with several key standards to ensure comprehensive safety coverage:

• IEC 61513 – Nuclear power plants – Instrumentation and control systems – General requirements for systems important to safety. IEC 61226 complements IEC 61513 by focusing on categorization and classification.

• IAEA SSR 2/1 – Safety Requirements for Design of Nuclear Power Plants. IEC 61226 aligns terminology and criteria with this IAEA publication.

• IAEA SSG-30 – Safety Guide on Instrumentation and Control Systems. IEC 61226 reflects recent recommendations outlined in this guide.

• Other IEC standards for environmental testing, electrical equipment, and quality assurance – Maintain harmony with required environmental and quality criteria for nuclear safety systems.

By adopting IEC 61226:2020, nuclear power plants can implement a robust, internationally recognized framework for classifying safety functions and their associated instrumentation and power systems, ensuring sustained safety performance under normal operation and potential accident scenarios. This facilitates improved safety management, harmonization with global standards, and compliance with regulatory expectations.