General Terminology

Question 1

Abnormally Distributed Uncertainty

Answer 1

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.

Question 2

Accuracy

Answer 2

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.

Question 3

Allowable Setpoint

Answer 3

A setpoint with no margin applied. (see Setpoint and Margin)

Question 4

Allowable Value

Answer 4

A limiting value that the trip setpoint may have when tested periodically, beyond which appropriate action shall be taken.

Question 5

Ambient Temperature

Answer 5

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.

Question 6

Analytical Limit

Answer 6

Limit of a measured or calculated variable established by the safety analysis to ensure that a safety limit is not exceeded.

Question 7

As Found

Answer 7

The condition in which a channel, or portion of a channel, is found after a period of operations and before calibration (if necessary).

Question 8

As Left

Answer 8

The condition in which a channel, or portion of a channel, is left after calibration or final actuation device setpoint verification.

Question 9

Bias

Answer 9

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.

Question 10

Bistable

Answer 10

A device that changes state when a preselected signal value is reached. For example, for BWRs electronic trip units are considered bistables.

Question 11

Calibration

Answer 11

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.

Question 12

Components

Answer 12

Discrete items from which a system is assembled. For example, wire, resistors, transmitters, converters, etc. would all be considered components.

Question 13

Conformity

Answer 13

The closeness that the output of an instrument approximates (or conforms to) a specified preprogrammed curve (e.g., logarithmic, parabolic, cubic, etc.).

Question 14

Dead Band

Answer 14

The range through which an input can be varied upon reversal of direction without initiating an observable output response.

Question 15

Dependent Uncertainty

Answer 15

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.

Question 16

Design Basis

Answer 16

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.

Question 17

Design Limit

Answer 17

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.

Question 18

Device

Answer 18

An apparatus for performing a prescribed function (i.e., an instrument). The discrete items which make up an instrument loop/channel.

Question 19

Drift

Answer 19

An undesired change in output over a period of time, which change is unrelated to the input, environment, or load.

Question 20

Dynamic Response

Answer 20

The behavior of the output of a device as a function of the input, both with respect to time.

Question 21

Effect

Answer 21

A change in output produced by some outside phenomena, such as elevated temperature, pressure, humidity, or radiation.

Question 22

Error

Answer 22

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.)

Question 23

Final Actuation Device

Answer 23

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.

Question 24

Foldover

Answer 24

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.

Question 25

Full Scale

Answer 25

The 100% value of the measured parameter on an instrument. Full scale is equal to the span for zero-based instruments.

Question 26

Harsh Environment

Answer 26

This term refers to the worst environmental conditions to which an instrument is exposed during transient, accident or post-accident conditions, out to the point in time when the device is no longer called upon to serve any monitoring or trip function. It may also be referred to as the accident environment, or trip environment, and is the converse of mild environment.

Question 27

Hysteresis

Answer 27

That property of an element evidenced by the dependence of the value of the output, for a given excursion of the input, upon the history of prior excursions and the direction of the current traverse.

Question 28

Independent Uncertainty

Answer 28

Uncertainties are independent of each other if their magnitudes or algebraic signs are not significantly correlated, and they do not share a common source.

Question 29

Indicated Value

Answer 29

A predetermined value of an indicator or recorder at which a manual action will be taken. An indicated value is similar to a setpoint except that a setpoint assumes an action will be taken by a device and an indicated value assumes an action will be taken by an individual.

Question 30

Instrument

Answer 30

A single device that may be utilized alone or interconnected with other instruments for the purpose of observation, control and/or protection of a process or parameter.

Question 31

Instrument Channel

Answer 31

An arrangement of components and modules as required to generate a single protective action signal when required by a plant condition. A channel loses its identity where single protective action signals are combined. For example, if three channels are input into a comparator, at the comparator the three individual signals lose their identity. Thus, the three channels are only channels up to the comparator.

Question 32

Instrument Range

Answer 32

The region between the limits within which a quantity is measured, received, or transmitted, expressed by stating the lower and upper range values.

Question 33

Insulation Resistance (IR) Effect

Answer 33

The change in measurement signal due to an increase in leakage current between the conductors of instrument signal transmission components such as cables, connectors, splices, etc. The increased leakage is caused by the decrease of component insulation resistance due to extreme changes in environmental conditions.

Question 34

Lead Wire Effect

Answer 34

The effect on measured RTD signals due to ambient temperature changes on the RTD signal wire.

Question 35

Limiting Safety System Setting (LSSS)

Answer 35

Settings for automatic protective devices in nuclear reactors that are related to those variables having significant safety functions. A LSSS is chosen to begin protective action before the analytical limit is reached to ensure that the consequences of a design basis event are not more severe than the safety analysis predicted. Limiting Safety System Settings are identified in Section 2.0 of the Technical Specifications.