Degradation Trending

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may be converted to a measurement method practical for repeated application, or life extension

techniques needed to achieve the desired lifetime for the facility may be finalized.

Results of activities in earlier MCA phases should be forwarded as recommendations to the design

authority for consideration as new design requirements. New design requirements should include

actions related to periodic monitoring and trending of aging degradation, as well as actions related to

life extension. To support these new design requirements, the aging degradation evaluations should

also be provided as design basis. The appropriate line organizations, such as operations, or

maintenance, carry out the approved new design requirements on an ongoing basis. For example,

slower, stress-reducing operations (e.g., heatups, cooldowns) to extend facility lifetime are

implemented through operations procedures. Periodic aging measurements may be performed by

either the maintenance or system engineering organizations.

For the periodic monitoring, this involves fine-tuning the technical aspects of the periodic

measurements for ease of use, error avoidance, and operational efficiency. In addition, it involves

establishing appropriate frequencies for monitoring actions for different types of equipment, as well as

requirements and methods for trending the results of those measurements and for extrapolating the

trend to anticipate end of life. The resulting extrapolated lifetimes should be used to update the

previously determined lifetimes.

4.4.1 DEGRADATION TRENDING

The purposes of degradation trending are to determine whether the degradations are progressing as

expected and to identify corrective actions that may be necessary to achieve the component or facility

lifetime. The analysis of data obtained by MCA periodic material condition measurements may show

that component degradation is occurring faster or slower than expected. This new information may

lead to revisions of the remaining lifetime determination, revising the life extension techniques, or some

combination of both.

To ensure that the desired facility lifetime is achieved, it is necessary to monitor the components most

likely to affect the facility lifetime, the components for which the lifetime is uncertain, and the

components that need life extension techniques to achieve the desired facility lifetime. Consideration

should also be given to adding measurements that are designed to detect unexpected degradation of

the components. Often, it is the unexpected that causes a component to fail before the end of its life.

For example, it was discovered in the commercial nuclear industry that thermal stratification of the liquid

inside pipes connected to pressurizers can cause stresses in the pipe wall that can lead to failure. Yet,

these stresses had not been anticipated in the design process. The final selection of measurements

should take into account the significant failure modes, degradation mechanisms that could cause

unexpected failures, and the practicality of obtaining these measurements.

The baseline measurements of the current condition of included components identify techniques that

successfully measured critical physical characteristics and those techniques that did not. The baseline

measurements show where improved or alternate measurement techniques are needed.

A list of potential measurements is then developed. These are termed "potential measurements" for

two reasons: (1) more measurements may have been identified than are actually necessary (in some

cases, the initial baseline results do not warrant repeating the measurements on a periodic basis); or

(2) the total number of measurements may not be consistent with the overall capability of the facility for

obtaining and analyzing the volume of information that will result from these repeated measurements

over the long term. Also, alternative or improved measurement techniques may be identified that have

not been previously obtained at the facility. It will be necessary to confirm that these techniques are

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