BS EN IEC 60709:2019

1.1 General This document is applicable to nuclear power plant instrumentation and control (I&C) and electrical systems and equipment, whose functions are required to be independent due to their contribution to: a redundant or diverse safety group; different defence in depth levels; different safety classes and also with non-classified (NC) systems.It is also applicable to temporary installations which are part of those I&C and electrical systems important to safety (for example, auxiliary equipment for commissioning tests and experiments or mobile power supply systems). Clause7 is intended particularly for electrical isolation, Clause8 is intended particularly for the cabling and the arrangement of equipment of I&C and electrical systems important to safety. This document applies to I&C and electrical systems of new nuclear power plants and to I&C and electrical upgrading or back-fitting of existing plants. For existing plants see1.2 and 5.4. Where independence is required by general safety standards such as IAEA safety guides, IEC61513 (for I&C), IEC63046 (for electrical systems) and other project constraints, one aspect of achieving this independence is physical separation and electrical isolation between the systems and their equipment that perform safety functions. This document defines the assessments needed and the technical requirements to be met for I&C and electrical systems, equipment or cables for which separation is required. Those means are to achieve adequate physical separation and electrical isolation between redundant sections of a system and between a higher and lower class systems. This separation is needed to prevent or minimise the impact on safety that could result from faults and failures which could be propagated or affect several sections of a system or several systems. The requirements for functions, and their associated systems and equipment, to be independent are normally defined in detail in the project documentation; the method of determining and defining these requirements is not the subject of this document. Following IAEA SSR-2/1 Requirement 21, separation means by physical separation, electrical isolation, functional independence and independence of communication are considered. In this document physical separation and electrical isolation are treated. Functional independence and independence of communication are not considered in this document. More details referring to functional independence, independence from control systems and independence of communication are given in Annex D.1.2 Application: new and pre-existing plants This document applies to the I&C and electrical of new nuclear power plants as well as to up-grading or back-fitting of existing plants. For existing plants, only a subset of requirements is applicable and this subset is normally specified and argued at the beginning of any project.