Nuclear power plants – Instrumentation, control and electrical power systems important to safety – Categorization of functions and classification of systems
|Publication Date:||1 April 2020|
|ICS Code (Nuclear power plants. Safety):||27.120.20|
This document establishes, for nuclear power plants2, a method of assignment of the functions specified for the plant into categories according to their importance to safety. Subsequent classification of the I&C and electrical power systems performing or supporting these functions, based on the assigned category, then determines relevant design criteria.
The design criteria, when applied, ensure the achievement of each function in accordance to its importance to safety. In this document, the criteria are those of functionality, reliability, performance, environmental qualification (e.g. seismic) and quality assurance (QA).
This document is applicable to:
• the functions important to safety that are performed by I&C systems and supported by electrical power systems (categorization of I&C functions),
• the I&C systems that enable those functions to be implemented (classification of I&C systems),
• the electrical power systems that support those functions (classification of electrical power systems).
The systems under consideration provide automated protection, closed or open loop control, information to the operating staff, and electrical power supply to systems. These systems keep the NPP conditions inside the safe operating envelope and provide automatic actions, or enable manual actions, that prevent or mitigate accidents, or that prevent or minimize radioactive releases to the site or wider environment. The I&C and electrical power systems that fulfil these roles safeguard the health and safety of the NPP operators and the public.
This document follows the general principles given in IAEA Safety Requirement SSR-2/1 and Safety Guides SSG-30, SSG-34 and SSG-39, and it defines a structured method of applying the guidance contained in those codes and standards to the I&C and electrical power systems that perform functions important to safety in a NPP. This document is read in association with the IAEA guides together with IEC 61513 and IEC 63046 in implementing the requirements of the IEC 61508 series. The overall classification scheme of structures, systems and components for NPPs can be summarized as follows by Figure 1.
This 2-phase process is defined for purpose of comprehensiveness; it enables the capture of all the functions and all the systems important to safety, including I&C systems, as well as electrical power systems.
In this scheme, functions are defined and categorized regardless of the physical means that are implemented to fulfill them. In the framework of this document, the functions to be categorized are performed by I&C systems. Accordingly, they are called I&C functions.
This document applies to I&C and electrical power systems for new nuclear power plants as well as for modification and modernization of existing plants.
For existing plants, only a subset of requirements can be applicable, and this subset is identified at the beginning of any project.
2 The scope of this document is consistent with IAEA SSR-2/1 and SSG-30, upon which it is based.