BS IEC 61497:1998 pdf download – Nuclear power plants ——Electrical interlocks forfunctions important to safety — Recommendations for design and implementation

BS IEC 61497:1998 pdf download – Nuclear power plants ——Electrical interlocks forfunctions important to safety — Recommendations for design and implementation.
Interlock functions on nuclear power plants prevent unsafe conditions or operations, protect personnel and prevent hazards. Interlock functions prevent actions which could lead to or increase danger or damage to the plant, and do not normally take steps to correct conditions. Interlock functions may limit a continuing action in order to prevent a condition developing, or may prevent a possible action and thereby prevent a condition. Interlock functions may generate a permissive signal to allow selection of the output of an instrument only when in its operating range, for use by the reactor protection system or a control system for the current power, temperature range or condition.
Interlock functions may he provided by mechanical means or by administration, by operator action or by electrical methods. Administration is tinder control of the plant management, and involves signatures on permits and records of authority to perform operations, which are not discussed. Such methods may he used to control personnel access to an active area, to permit operator use of a control, to authorize issue of a key which can release a locked control or which allows access to perform some operation for special or non-routine reasons.
Electrical methods include use of the reactor protection system. logic within control systems, logic in computer-based equipment, interconnections in switchgear and dedicated units of relay or solid-state logic. Typical interlock functions and methods of providing electrical interlocks are given in Annex A.
The nuclear safety requirements for interlocks may be in addition to or different from the interlock requirements for fire protection, personnel safety or plant protection. These requirements may conflict and guidance is given on resolution of conflicts.
The requirements for classification and for reliability of instrumentation and control systems important to safety are discussed in IEC 61226. Electrical interlocks require classification according to that 8tandard to identify basic requirements. Some requirements for safety system interlocks can be derived from IAEA 50.SG.D3, but not for all interlocks important to safety. The system, design, reliability and equipment requirements appropriate to categories A, B and C are developed in this standard.
Interlock functions exist in many systems on a nuclear plant, which can result in different approaches to their implementation in different systems. They should therefore be implemented in a consistent manner throughout a plant. This standard is concerned with the practical implications of electrical interlock design and implementation to meet the levels of performance, reliability and consistency required on nuclear plants.
1 Scope
This International Standard provides recommendations for the design and implementation of electrical interlocks used actively or passively to prevent unsafe conditions or to ensure specific safe conditions and states during the operation of nuclear power plants. Safety system interlocks are covered by standards for safety systems.
This standard gives design, reliability and test criteria arising from the consideration of interlocks important to safety in accordance with IEC 61226. It uses categories A. B and C as defined by that document. It takes into account the interlock safety significance and functions, and the role of the operator in some interlocks.
Guidance is given on redundancy and on diversity of equipment for implementing interlocks, where high availability or integrity is involved, or where common mode failure may limit reliability.
The use of computer-based equipment for interlock functions is discussed, and recommendations for diversity are given. Requirements for software and for verification and validation are given by reference to IEC 60880.
The provision of test facilities is discussed together with self-testing and self-monitoring methods. The system of interlocks for a specific function includes the sensors of plant state (e.g.. measuring devices and limit switches), the interlock and control power supplies, the control and instrumentation equipment providing the particular logic function for prevention or limitation of operation. and the cables, electromechanical features, key control and administrative control associated with the function.