Functionally Critical Equipment Selection

DOE-STD-1052-93

The definition of what constitutes a failure is of primary importance. A clear

distinction should be made between degraded performance and functional failure.

Whenever a failure is defined by some level of performance, condition, or dimension,

the appropriate standards should be stated to provide the basis for establishing

whether a failure has occurred. For example, heat exchanger tube fouling may cause

water temperature to exceed an allowable temperature. This would be considered

a failure. Any temperature below the allowable value, but above the normal

operating temperature, would be considered degraded operation. Component

performance standards are determined from descriptive and operating information

sources such as plant technical safety requirements, operating procedures, and design

requirements.

7.7

Functionally Critical Equipment Selection

After functional failures are identified, functionally critical equipment (FCE) is

identified by analyzing the functional failures. Functionally critical equipment are

components within a system or a subsystem that meet the following criteria:

components whose failure results in a system functional failure

components whose failure frequency and severity have an adverse impact on

plant operation

Selection of FCE may be performed by analyzing the effects of a failure of the

component on the system functions. If failure of the component may cause a loss of

system function, the component is considered as FCE. In addition, the results of a

PRA or other model may indicate that a component is functionally critical. The

following items also should be considered in the selection and prioritization of FCES:

individual plant examination

importance to nuclear safety

safety system functional inspections

operating and maintenance history

plant operating experience

component failure analysis report (CFAR)

radiation exposure attributed to maintenance on the component

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