Facility Grades and SSC Grades cont'd

DOESTD107393

attention where such attention is not warranted. It is important that the grading system include

consideration of both the overall facility importance grade and the importance grades for the SSCs

within the facility.

The graded approach for the CM program is based on hazard. Hazard is related to the worst possible

accident, without regard for either the physical SSCs or the administrative programs (such as safety

reviews, QA programs, procedures, and training) intended to prevent, detect, or mitigate potential

accidents. Hazard considers the material types, quantities, forms, locations, dispersibility, and

interaction with available energy sources that could cause harm to personnel or the environment.

Hazard is a measure of the unmitigated consequences of source terms; it provides an indication of the

importance of having SSCs and administrative controls that prevent, detect, or mitigate accidents. In

contrast, risk is a measure of the combination of the probability of the occurrence and the

consequences of such an occurrence. In risk assessments, the SSCs and administrative controls are

assumed to function. By providing these SSCs and administrative controls, the risks associated with

the operation of hazardous facilities become acceptably small. Risk is a measure of both the hazard

and the effectiveness of the SSCs and administrative controls. Because the purpose of grading often

relates to the value of improvements, it is appropriate to use hazard, or unmitigated risk, rather than

risk to gauge importance.

Facility Grades. Determination of facility grades involves consideration of the hazard category, the

programmatic mission, and the complexity of the facility. Therefore, the facility grade reflects the

overall importance of the facility and is a broader consideration than the hazard category.

In keeping with its established policy that safety be given priority over programmatic

considerations, DOE has focused initial development of the facility grading process on nuclear

hazards. DOE-STD-1027-92, Hazard Categorization and Accident Analysis Techniques for

Compliance with DOE 5480.23, Nuclear Safety Analysis Reports, provides guidance for

evaluating facility hazards. Chemical and other hazards are also being considered. DOE

recognizes that at some nuclear facilities, the dominant hazard may not be a nuclear hazard but

rather some other type of hazardous material, such as sulfuric acid or chlorine. The hazard

category of any facility, nuclear or non-nuclear, should be based on the dominant hazard. Some

DOE facilities have already evaluated their nuclear hazards. If a facility has a DOE-approved

hazard category, it should be incorporated into the facility grade.

The degree of implementation necessary to maintain adequate safety varies with facility size and

complexity. Large, complex facilities such as plutonium reprocessing facilities or production reactors

generally have more SSCs and therefore more opportunities for failure than less complex facilities

such as dry storage vaults. Similarly, if a facility is small and uncomplicated, such as a waste storage

tank, its safety may depend more heavily on manual actions than on automatic safety actions. In

situations that depend heavily on manual safety decisions and actions, the man-machine interface

becomes more important.

Pending the development of detailed DOE guidance, judgment should be used to estimate the

relative programmatic mission importance and complexity of the facility. Those estimates would then

be merged with the hazard category to arrive at an overall facility importance grade. The facility

grade should be a reasonable estimate of the overall importance of the facility, regardless of the

method used to arrive at that estimate.

SSC Grades. Importance grading of SSCs is needed to determine the level of controls appropriate for

various functions of the CM program. Such grading is not new; DOE has graded nuclear facility

systems into safety-class systems and nonsafety-class systems for years. SSC grading is a measure

of the relative importance of SSCs, based upon the most important design requirements applicable to

each SSC. SSC grading should be based on the functions (design requirements) that the SSC

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