Preventive Maintenance Task Selection

DOE-STD-1052-93

Class C (Economics) - Failure modes that affect support functions and do not

cause a power reduction greater than 20 percent. Scheduled maintenance or

a design modification is necessary to reduce the corrective maintenance cost.

Class D (Hidden failures) - Failure modes of standby or infrequently used

components that do not affect personnel and/or reactor safety and are not

evident to the operating crew. Scheduled maintenance is necessary to reduce

the likelihood of multiple failures to an acceptable level. Hidden failures are

reclassified using the LTA as either A, B1, B2, or C to establish priority of

task selection.

Significant failure modes should be addressed in the following order: A, B1,

B2, and C. This information should be used in the selection of applicable and

effective PM tasks.

8.1.2 Preventive Maintenance Task Selection

This section describes the method for selecting applicable and effective PM

tasks to control the failures of significant failure modes. The PM task

selection portion of the LTA is used in this method.

Four basic categories of PM tasks are described below. Special emphasis

should be placed on selecting condition-monitoring tasks when they are

applicable. If a failure mode provides any indicators of degradation of a

component, baseline values should be set for the degradation and a regular

monitoring program established for the component. When scheduling permits,

multiple tasks should be combined into single activities. The following are the

categories of PM tasks:

TIME-DIRECTED TASK - A task performed solely on the basis of a

fixed time schedule, safe life limits, or economic life limits (e.g., change

the air filters in the instrument air system every 30 days). The scheduled

replacement of a component at its end-of-life is a time-directed

replacement task. A time-directed task may be ineffective if not

performed at an appropriate interval. For example, a premature overhaul

not only wastes resources but also increases the risk of human error

during the removal, overhaul, and reinstallation process. In addition,

premature overhauls may result in unnecessary radiation exposure and

excessive equipment unavailability.

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