IEC 61888 pdf download – Nuclear power plants – Instrumentation important to safety – Determination and maintenance of trip setpoints
1scope
This standard defines the requirements for assuring that automatic setpoints for nuclearsafety system instrumentation (as defined in clause 3), are established and maintained withinspecified limits in nuclear power plants and nuclear reactor facilities.
2Normative 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 editionof the referenced document (including any amendments) applies.
IEC 60050-394:1995,International Electrotechnical Vocabulary (IEV) – Chapter 394:∶Nuclearinstrumentation: 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 tosafety – General requirements for systems
IAEA NS-R-1:2000,Safety of nuclear power plants: Design
3 Definitions
For the purposes of this document, the following terms and definitions apply.
NOTE Additional definitions related to instrumentation terminology may be found in lEC 60050-394.
3.1
allowable value
a limit value that the trip setpoint may have when tested periodically， beyond whichappropriate action shall be taken
3.2
analytical limit (of setpoint)
limit of a measured or calculated variable established by the safety analysis to ensure thata safety limit is not exceeded.The margin between the analytical limit (of the setpoint) andthe 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 operationand before recalibration (if necessary)
3.4
as left
the condition in which a channel,or portion of a channel,is left after calibration or finalsetpoint 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 foractuated 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 signalthat 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 signsare not significantly correlated
3.10
instrument channel
an arrangement of components and modules，including sensor(s), as required to generate asingle 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, lsexpressed 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 protectivedevices 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 andmonitoring 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 formsuitable for measurement
3.15
random
variable whose value at a particular future instant cannot be predicted exactly but can only beestimated 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 underspecified operating conditions
3.17
safety limit
a limit on an important process variable，,necessary to reasonably protect the integrity ofphysical 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 thereactor and the heat removal from the core and/or to limit the consequences of anticipatedoperational occurrences and design basis accident conditions (see lEC61513)
3.19
saturation
device characteristic exhibited when a further change in the input signal produces noadditional change, or progressively less change,in the output
3.20
sensor
portion of a channel that responds to changes in a plant variable or condition and converts themeasured process variable into a signal, for example, electric or pneumatic
3.21
test interval
elapsed time between the initiation (or successful completion) of tests on the same sensor,channel, load group, safety group, safety system, or other specified system or device
3.22
trip setpoint
predetermined value for actuation of the final setpoint device to initiate a protective action
3.23
channel uncertainty
the amount to which an instrument channel’s output is in doubt (or the allowance madetherefore) due to possible errors,either random or systematic,that have not been corrected.The channel uncertainty is generally identified within a probability and confidence level.
IEC 61888 pdf download – Nuclear power plants – Instrumentation important to safety – Determination and maintenance of trip setpoints
