Assessment of System-Interaction Related Target Failure Potential

DOE-STD-1021-93

installation of anchors or braces (for earthquake, wind, and tornado loads) or placing the

component at a different elevation or location (for flooding situations) will enable the component

to withstand the NPH effects (i.e., the component will qualify at least as a PC-1). In some cases,

it is often more cost-effective to do so rather than to demonstrate that the component is not

important from life safety or mission considerations (especially to determine the effect of its

failure on other safety-related or important components). On the other hand, there are cases in

which the component location and/or configuration is such that providing, for example, required

seismic braces or anchorages can be so difficult that it is more costly than replacing the

component itself. In such cases, the component should be assigned to PC-0.

"Engineering judgment" will play a big role in determining the performance category of these

components. Such judgment should be exercised with emphasis on the "graded approach"

philosophy. Accordingly, the level of effort for such categorization should generally be at par

with that usually spent for identifying "essential" facilities when a International Building Code

(IBC 2000) type of design is adopted.

3.7

Assessment of System-Interaction Related Target Failure Potential

To account for adverse system interaction, Subsection 2.5, Paragraph (c)(i), requires an assessment

of the failure potential of the target component, given the failure of the source component.

Depending on the physical and functional complexity of the target and the nature of its interaction

with the source, the level of effort for assessing this target failure potential can vary. Following the

"graded approach" philosophy, the rigor with which such failure potentials are to be determined

should depend on the safety significance and the preliminary performance category of the target, the

hazard category of the facility, and the relative costs of various methods of determining target

failure potentials.

In the following paragraphs, two methods of assessing target failure potentials are presented in

order of decreasing rigor:

(a) Systematic Analysis Method

Target failure potentials can be assessed using a qualitative but systematic approach by

constructing a fault-tree of the scenario. If justifiable from cost-benefit considerations, this

may be a desirable method when necessary data for fault tree construction are available.

Generally, it should be used when the failure of the target is dependent on a large and complex

chain of events that may follow the failure of the source, or to qualify a large system in its

entirety. Component-by-component application of this method is unlikely to be cost-effective.

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