Assignment of Component Grades

DOESTD107393

In establishing boundaries between facility systems and essential supporting systems, arbitrary but

reasonable boundaries may be defined. Essential support services include electric and control power,

instrument air, lubricating oil, and ventilation.

There are two primary approaches, one recommended and one alternate, for establishing system

boundaries for essential support systems. The recommended approach is to extend the safety system

boundaries to include essential support items out to an appropriate interface, such as an isolation valve.

The alternate approach Is to deem the essential support systems to have safety portions. According to

the recommended approach for air-operated equipment, the air controller, solenoid switches, and air

isolation valves would be considered part of the basic safety system, while equipment upstream of the

valve would be considered part of the instrument air system. According to the same approach for

electrically operated equipment, the electrical components, including limit switches, out to and including

the first breaker, would be considered part of the basic safety system, and the components upstream of

the breaker would be considered part of the electric power system.

Assignment of Component Grades. Component grades should be assigned in a manner analogous to

system grading. Best Available Design Information should be used to identify the design requirements

associated with each component and determine the design requirement types associated with each

component. In some cases, the design requirements might indicate that a component is not essential to

the system's top-level function. For example, a safety cooling-water system might have a chemical

release monitor with an environmental design function, but no safety design function. Component

grades should be assigned on the basis of the applicable types of design requirements. The component

grade should be based on the most important type of applicable design requirements.

As previously stated, the default component grade is the same as the system grade. In many cases, the

component is graded consistently with its system. The net result of component grading may be the

downgrading of certain components that are not essential to the top-level category of design

requirements for the system. For example, local instrumentation to support maintenance might not be

needed to fulfill either safety, environmental or mission requirements. If there is any doubt with regard to

downgrading a component, the component should retain the system grade until associated design

requirements are fully reconstituted. If a component appears to have design requirements of a higher

grade than its system, the system might be incorrectly graded or the component might be in the wrong

system.

With the exception of components whose design requirements have been established and found to be

adequate and outside the equipment scope criteria, all components within a CM system should be

included in the CM program, even those without a safety, environmental, or mission function. Once the

design requirements are fully established and adequate, the CM equipment scope criteria may be used

to consider component exclusions. However, the inclusion of components other than safety,

environment, and mission ones is generally advisable for CM systems to enhance overall configuration

control.

As with system grading activities, other ongoing activities will periodically identify new information

relevant to component grading. New design activity, for example, might add new systems as well as

new components to existing systems. The DR adjunct program might uncover facility design

requirements that affect component grading. Moreover, system walkdowns or operational activities

might identify previously overlooked components. The impact of new information on component grading

should be taken into consideration. While component grading is generally a one-time activity, its results

are subject to review and revision as necessary when new information becomes available.

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