Application of the Graded Approach cont'd

DOE-STD -3009-94

and/or fault trees form the bases for physical phenomena modeling and engineering

analysis. The level of analytical effort employed is primarily a function of magnitude of

hazard, but also takes into account system complexity, and the degree to which detailed

modeling can be meaningfully supported by system definition. For nonreactor nuclear

facilities, these considerations do not support a need for probabilistic/qualitative risk

assessment of overall facility operations. This Standard does not present an expectation of

or a requirement for probabilistic/qua litative risk assessment. Additionally, in accordance

with DOE-STD-1027, the hazard analysis as described in Section 3.3, "Hazard Analysis,"

of this Standard is sufficient to meet the 10 CFR 830 requirements of accident analysis for

Hazard Category 3 facilities. The hazard analysis should be adequate to provide a simple

estimate of bounding consequences for Hazard Category 3 facilities.

It must be kept in mind that Hazard Category 3 facilities may also have chemical hazards.

The hazard classification mec hanism used in DOE-STD-1027 does not consider the

potential hazardous chemical releases. The results of the hazard analysis will indicate

whether a facility contains significant chemical hazard(s) that may necessitate accident

analysis.

Accident analysis is also inherently graded in terms of the degree of physical modeling and

engineering analysis needed to quantify accident consequences and likelihood. The use of

bounding assumptions and less detailed physical modeling in accident analysis is

appropriate. For example, where a given release has low consequences even if a filtered

ventilation system is bypassed, detailed modeling of filtered release parameters such as

filter differential pressure, plenum temperature, etc, is not needed for the given accide nt.

Formal, quantitative analysis of potential accident sequences as described in Section 3.4,

"Accident Analysis," is not required to assess worker safety issues in addition to the

hazard analysis. The largely qualitative hazard evaluation described in Section 3.3,

which is a thorough analysis of potential accidents, is a more relevant vehicle for worker

safety assurance.

Additional guidance on hazard and accident may be gained from the following

references:

Guidelines for Hazard Evaluation Procedures, American Institute of Chemical

Engineers, 1992.

"Hazard Categorization and Accident Analysis Techniques for Compliance with

DOE Order 5480.23, Nuclear Safety Analysis Reports" DOE-STD-1027.

"Recommended Values and Technical Bases for Airborne Release Fractio ns

(ARFs), Airborne Release Rates (ARRs), and Respirable Fractions (RFs) at DOE

Non-Reactor Nuclear Facilities" DOE Handbook (HDBK)-3010.

Nuclear Fuel Cycle Facility Accident Analysts Handbook, Nuclear Regulatory

Commission NUREG-1320.

"A Strategy for Occupational Exposure Assessment," American Industrial

Hygienists Association, 1991.

"Application of Hazard Evaluation Techniques to the Degree of Potentially

Hazardous Industrial Chemical Processes," National Institute of Occupational

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