Detailed Aging Degradation Evaluations

DOESTD107393

Life-limiting components are selected by applying predetermined evaluation criteria to the components

that were identified as potentially life-limiting, with each component given a score for each criterion.

The evaluation criteria should include consideration of:

Feasibility of replacement

Replacement schedule, including outage duration (facility downtime)

Replacement cost

Impact on adjacent structures

Disposal and transportation difficulties

Service environments (corrosion/erosion, dynamic loading, radiation, environmental

conditions, and synergistic effects)

Safety

Issues that are specific to the facility

Each evaluation criterion should be assigned a weighting factor that is applied to its score, with the

considerations that are most critical to facility life having the highest weighting factors. The combination

of the score and the weighting factor determines the total score for each consideration. The total score

for each potentially life-limiting component is the summation of the total scores for each consideration.

This scoring is performed for each potentially life-limiting component.

Because the score that a component receives for each criterion depends on the knowledge and

experience of the scorer, it is recommended that at least two teams perform the evaluations. These

teams should consist of individuals who are experienced in the design and operations of the facility and

who are supported by personnel trained or experienced with MCA. The teams should work

independently during the initial scoring process. Subsequently, representatives from each team should

meet to resolve differences and generate a consensus composite score for each component.

Once the scoring process has been completed, the final selection criteria for the life-limiting

components may be a threshold value for the consensus composite score of a component or some

other criterion that appropriately identifies life-limiting components.

Concurrent with this activity, SSCs within the CM program may be screened to identify SSCs that,

although not life-limiting, should be reviewed in more detail to evaluate aging. A review of the non-life--

limiting components may indicate that aging management should be adopted as a matter of good

practice. If the failure of certain SSCs may have a significant impact on safety or mission, evaluation

may be appropriate. Because of the potentially severe impact, it is desirable to avoid failure of some

types of equipment. For example, a facility may have so many electrical cables and cable trays that

special attention to them is warranted. Similarly, if a facility has several hundred motor-operated

valves, this type of equipment may warrant special attention. This SSC review should be coordinated

with other programs, such as the maintenance program.

4.2.3 DETAILED AGING DEGRADATION EVALUATIONS

The purpose of detailed aging degradation evaluations is twofold: (1) to identify mechanisms that

determine the lifetime of components and (2) to provide for observations or measurements that define

the condition of life-limiting components. This information is necessary to the final determination of

facility remaining lifetime, the feasibility of continued operations, and the definition of the ongoing MCA

program. This activity includes performing the following steps for each component:

Develop full description of the component.

Identify significant aging mechanisms.

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