IEC 61888 pdf download.Nuclear power plants – Instrumentation important to safety – Determination and maintenance of trip setpoints
This standard defines the requirements for assuring that automatic setpoints for nuclear safety system instrumentation (as defined in clause 3), are established and maintained within specified limits in nuclear power plants and nuclear reactor facilities.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60050-394:1995, International Electrotechnical Vocabulary (IEV) – Chapter 394: Nuclear instrumentation: Instruments IEC 60671, Periodic testing and monitoring of the protective system of nuclear reactors IEC 61513:2001, Nuclear power plants – Instrumentation and control for system important to safety – General requirements for systems IAEA NS-R-1: 2000, Safety of nuclear power plants: Design
For the purposes of this document, the following terms and definitions apply. NOTE Additional definitions related to instrumentation terminology may be found in IEC 60050-394. 3.1 allowable value a limit value that the trip setpoint may have when tested periodically, beyond which appropriate action shall be taken 3.2 analytical limit (of setpoint) limit of a measured or calculated variable established by the safety analysis to ensure that a safety limit is not exceeded. The margin between the analytical limit (of the setpoint) and the safety limit allows to take into account: – the response time of the instrument channel, – the range of transients due to the considered accident.3.3 as found the condition in which a channel, or portion of a channel, is found after a period of operation and before recalibration (if necessary) 3.4 as left the condition in which a channel, or portion of a channel, is left after calibration or final setpoint device setpoint verification 3.5 drift an undesired change in output over a period of time where change is unrelated to the input, environment, or load 3.6 error the algebraic difference between the indication and the ideal value of the measured signal 3.7 final setpoint device a component, or assembly of components, that provides input to the process voting logic for actuated equipment NOTE Examples of final setpoint devices are bistables, relays, pressure switches, and level switches. 3.8 foldover a device characteristic exhibited when a further change in the input produces an output signal that reverses its direction from the specified input-output relationship 3.9 independent uncertainty uncertainty components are independent of each other if their magnitudes or algebraic signs are not significantly correlated 3.10 instrument channel an arrangement of components and modules, including sensor(s), as required to generate a single protective action signal when required by a plant condition 3.11 instrument channel range the region between the limits within which a quantity is measured, received, or transmitted. Is expressed by stating the lower and upper instrument channel range values. 3.12 limiting safety system setting (LSSS) limiting safety system settings for nuclear reactors are settings for automatic protective devices related to those variables having significant safety functions 3.13 nuclear safety system instrumentation electronic and electrical equipment or instruments for ensuring the proper control and monitoring of a nuclear reactor, including all control and safety system instrumentation.3.14 primary element the system element that quantitatively converts the measured variable energy into a form suitable for measurement 3.15 random variable whose value at a particular future instant cannot be predicted exactly but can only be estimated by a probability distribution function 3.16 reference accuracy number or quantity that defines a limit that errors will not exceed when a device is used under specified operating conditions 3.17 safety limit a limit on an important process variable, ,necessary to reasonably protect the integrity of physical barriers that guard against the uncontrolled release of radioactivity 3.18 safety system system important to safety provided to ensure that in any condition, the safe shutdown of the reactor and the heat removal from the core and/or to limit the consequences of anticipated operational occurrences and design basis accident conditions (see IEC 61513)