General Terminology Flashcards
Abnormally Distributed Uncertainty
A term used by Reference 2.3 to denote uncertainties that do not have a normal distribution. For the purpose of this document, abnormally distributed uncertainties are treated as biases.
Accuracy
A measure of the degree by which the actual output of a device approximates the output of an ideal device nominally performing the same function. Error, inaccuracy, or uncertainty represent the difference between the measured value and the ideal value.
Allowable Setpoint
A setpoint with no margin applied. (see Setpoint and Margin)
Allowable Value
A limiting value that the trip setpoint may have when tested periodically, beyond which appropriate action shall be taken.
Ambient Temperature
The temperature of the medium surrounding a device. For field mounted devices, this is typically the room temperature at the device. For panel mounted devices, this is typically the temperature inside the panel which can be different from the room temperature.
Analytical Limit
Limit of a measured or calculated variable established by the safety analysis to ensure that a safety limit is not exceeded.
As Found
The condition in which a channel, or portion of a channel, is found after a period of operations and before calibration (if necessary).
As Left
The condition in which a channel, or portion of a channel, is left after calibration or final actuation device setpoint verification.
Bias
The fixed or systematic error within a measurement. The bias error is the fixed difference between the true value and the actual measurement. The bias error can be of (1) known sign and known magnitude, (2) known sign but an unknown magnitude (with a maximum), or (3) unknown magnitude (with a maximum) and unknown sign. Often times the sign and magnitude vary in some relationship with another parameter.
Bistable
A device that changes state when a preselected signal value is reached. For example, for BWRs electronic trip units are considered bistables.
Calibration
The comparison of a standard (or device of known accuracy) with equal or better accuracy with a device under test to detect, record, or eliminate by adjustment any variation in the accuracy of the device under test.
Components
Discrete items from which a system is assembled. For example, wire, resistors, transmitters, converters, etc. would all be considered components.
Conformity
The closeness that the output of an instrument approximates (or conforms to) a specified preprogrammed curve (e.g., logarithmic, parabolic, cubic, etc.).
Dead Band
The range through which an input can be varied upon reversal of direction without initiating an observable output response.
Dependent Uncertainty
Uncertainties are dependent on each other if they possess a significant correlation, for whatever cause, known or unknown. Typically, dependencies form when effects share a common cause.
Design Basis
That information that identifies the specific functions to be performed by an SSC and the specific values or ranges of values chosen for controlling parameters as reference bounds for design. These values may be (1) restraints derived from generally accepted “state of the art” practices for achieving functional goals, or (2) requirements derived from analysis (based on calculation and/or experiments) of the effects of a postulated accident for which an SSC must meet its functional goals (10CFR50.2, NGGM-PM-0007) or (3) requirements derived from analysis of operating and anticipated transient conditions in which the SSC is expected to perform its function.
Design Limit
The limit of a measured or calculated variable established to prevent undesired conditions (e.g., equipment or structural damage, spurious trip or initiation signals, challenges to plant safety signals, etc.). It is used in setpoint calculations for which there is no true Analytical Limit.
Device
An apparatus for performing a prescribed function (i.e., an instrument). The discrete items which make up an instrument loop/channel.
Drift
An undesired change in output over a period of time, which change is unrelated to the input, environment, or load.
Dynamic Response
The behavior of the output of a device as a function of the input, both with respect to time.
Effect
A change in output produced by some outside phenomena, such as elevated temperature, pressure, humidity, or radiation.
Error
The algebraic difference between the indication and the ideal value of the measured signal. (A “positive” error denotes that the indication of the instrument is greater than the ideal (actual) value.)
Final Actuation Device
A component or assembly of components that directly controls the motive power (electricity, compressed air, hydraulic fluid, etc.) for actuated equipment. Examples of final actuation devices are: bistables, relays, pressure switches, and level switches.
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.
