Determination of Failure Modes and Effects - Continued

DOE-STD-1052-93

6.6.4

If a failure mode only has a local effect, then no other analysis is needed for

that failure mode. Failure modes that have a plant effect and a high likelihood

of failure are considered significant and should be evaluated for PM task or

design changes. Failure modes that have a system effect are evaluated to

determine the significance of the failure effects and if the likelihood of

occurrence is high. The following questions may be used to determine if the

failure modes are significant:

Does the failure mode cause loss of a safety or system function?

Is the failure mode likely to occur?

NOTE:

Probability of occurrence of a failure is a consideration used

in several elements of the analysis. Specific probabilities or

the criteria to be used should be established by the plant.

Does the failure mode adversely affect plant availability or result in a

power reduction?

Could the failure mode result in personnel injury or significant

component damage?

Does the failure mode result in high use of maintenance resources?

Does the failure mode result in significant radiation exposure to

accomplish repair?

Does the failure mode impose excessive demand on other

components, considering a reasonable repair time, (e.g., on-off

cycling, uneven load distribution, or exceeding capacity ratings) that

may shorten the service life of other components?

6.6.5

If the answer to any of the above questions is "yes," the failure mode should

be addressed by a PM task or be evaluated for a possible design change to

eliminate or control the failure mode. If the answers to the questions are

"no," and the likelihood for failure is also low, then the failure mode is

considered to be insignificant since the consequences may be tolerated. If a

failure mode may be tolerated, it is not essential to perform a PM task to

mitigate the failure cause. If all failure modes may be tolerated, the

component should be considered for run-to-failure operation, and the existing

PM tasks for the component should be evaluated for possible deletion.

D - 15