The US approach

3.3.1. A case study from San Onofre Nuclear Generating Station

It is instructive to compare the RCM analysis steps for one specific RCM programme with the basic steps given in Section 3.1. The San Onofre RCM demonstration project is considered below for that purpose.

The major actions taken during the RCM analysis process at San Onofre are listed below:

(1) Define system boundary, partition into subsystems;

(2) Determine subsystem interfaces;

(3) Determine subsystem functions and out-interfaces;

(4) Provide functional failure modes;

(5) Review I;

(6) Collect data;

(7) Generate component listing, instrument matrix;

(8) Complete FMEA analysis;

(9) Complete instrument matrix;

(10) Complete CM history and design history reviews;

(11) Determine critical and non-critical components;

(12) Complete LTA analysis;

(13) Review II;

(14) Conduct interviews/PM and bases review;

(15) Evaluate non-critical components and PM recommendations;

(16) Finalize documentation.

These sections are consistent with the basic steps in Fig. 3-1, but there are several refinements and additions. The San Onofre actions explicitly identify reviews and interviews with plant personnel. This emphasizes the extreme importance of obtaining input from operations, maintenance and system engineers.

The San Onofre actions also include two additional items in the system analysis: a complete component listing and an instrument matrix. These items are included because the San Onofre RCM project critically reviews the current

maintenance for all equipment, even if it does not support an important function or if it is not critical equipment. The component listing assures completeness. The

instrument matrix is a table that clearly presents each instrument in a system and all of its functions. The instrument matrix expedites the analysis. An example

instrument matrix is presented in Fig. 3-9.

Finally, the San Onofre actions emphasize the production of final

documentation as the basis for the maintenance programme and as a starting point for the RCM living programme.

3.3.2. Other programmes in the USA

RCM methods in the nuclear industry have developed in an environment of open communications and technology transfer. As a result, most applications of RCM have conformed closely to the industry definition of RCM. They have

employed the same analytical steps and have used the same terminology for the most parts. Some of the very early work done prior to the EPRI Users Group and

demonstration projects was inappropriately labelled as RCM.

Nonetheless, there are some variations in the RCM analytical methods

employed by different utilities. For the most part, the differences are attributable to differences in the objectives that utilities have for their RCM studies, by the external organization of the utility or the amount of failure experience available and resources committed to the project. Some utilities tend to favour the selection of normally running production systems; others favour the selection of standby safety systems.

Although originally developed for application to normally running systems, there is nothing inherent in the RCM methods which would limit their application to one type system or another.

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EQUIPMENT F1 F2 F3 F4 FS F6 F7 F8 F9 F10 F11

Fl. Provides trip function (component, system, plant).

F2. Provides automatic control/interlock.

F3. Safety related display instrumentation.

F4. Supports tech.spec, surveillances.

F5. Provides alarm/indication to the control room.

F6. Instrument monitored on operator rounds.

F7. Computer input.

F8. Used to perform system or component design basis evaluation.

F9. Used during system manual operation.

F10. Needs to be operable but accuracy of indication is not essential.

FI1. Not required function.

Fig. 3-9. Instrumentation matrix for normal containment ventilation (GND).

Some utilities focus their investigation of dominant failure modes on operating and maintenance data and experience. Others develop their dominant failure modes primarily from an engineering evaluation of the system through FMEA or fault tree modelling. Either approach can be justified depending on the age of the plant, the quality of historical data and the availability of existing fault tree models and qualified personnel to use them.

Some utilities have deliberately excluded instrumentation from the system boundaries for RCM. They have elected to use other evaluation methods for these components. Others have developed an instrument matrix to replace the FMEA for instruments. This matrix enables the RCM analyst to determine and document all the functions of instruments in the system more efficiently and thoroughly.

RCM has recently been applied generically to a particular model of reactor coolant pump. This application of RCM to a single equipment type having multiple applications is consistent with the use of RCM for evaluating individual systems. The equipment is a complex assembly with several components and multiple functions. It can be treated effectively as a system with subsystems, in-interfaces and out-interfaces.

Even if the pump is considered as part of a larger system, it would certainly qualify as a functionally significant item in RCM terminology. The pump also has a very

narrow range of applications with similar environments and service life. Therefore, RCM can be generically applied to this item of equipment.

Finally, some variations in RCM methods are attributable to intentional links between the RCM programme and other plant programmes. One utility has an ambitious programme to reduce Tech.Specs required testing. Therefore, the RCM evaluation is careful not to consider Tech.Spec, action statements with the existing requirements. One utility has linked its RCM programme to their plant life extension programme. They explicitly seek PM activities to detect aging. Another RCM

application is specifically designed to make optimal use of an extensive new predictive maintenance programme. This utility will aggressively seek condition-directed tasks to replace its current time-directed activities. One utility has performed an RCM study on a system which has quantitative reliability goals. This RCM project will focus on identifying applicable and effective tasks to achieve these reliability goals.

One result of this variation in RCM applications is a wide range of costs per system within the industry. This wide range of costs is explainable by comparing the level of detail that is necessary to satisfy the wide range of utility objectives.