Determination of Failure Modes and Effects

DOE-STD-1052-93

7.8.3.3

The effects of the failure modes should be determined. Failure

modes should be evaluated at the local, system, and plant level

to determine their effects. When evaluating components with

redundant trains, consider the consequences of the failure mode

as if the redundant train was not available.

NOTE:

Considering the consequences of a component

failure as if redundant equipment is not available

is a conservative assumption that should result in

failures of most redundant safety components

being classified as single failures of safety system

functions. As such, these failures should be

evaluated since they meet the criteria of loss of

safety system function. There are analytical

techniques used to determine the consequences of

failures of redundant components. These

techniques are typically used in probabilistic risk

assessments that quantify risk and reliability.

Although usually manpower-intensive, using these

techniques may reduce the number of redundant

components that require an FMEA or change the

priority of the components to be evaluated.

Local effects are those that may be noted in the general vicinity of

the failure. System effects are problems that inhibit system

functions or operations. Plant effects are problems that impact

more than one system, constrain plant operation, or limit power

generation.

7.8.3.4

If a failure mode has only 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 tasks or design changes.

Failure modes that have a system effect are evaluated to

determine their likelihood of failure and the significance of the

failure effects. The following questions may be used to

determine if the failure modes with a system effect are

significant:

Does the failure mode cause loss of a safety or system

function?

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