Appendix B: Commentary on General NPH Design and Evaluation Criteria

DOE-STD-1020-2002

Appendix B

Commentary on General NPH Design and Evaluation Criteria

B.1 NPH Design and Evaluation Philosophy

The natural phenomena hazard (NPH) design and evaluation criteria presented in this

document (DOE-STD-1020) implement the requirements of DOE Order 420.1, "Facility Safety"

(Ref. B-1) and the associated Guides: "Guide for the Mitigation of Natural Phenomena Hazards

for DOE Nuclear Facilities and Non-nuclear Facilities" (Ref. B-2), "Guide for Nonreactor

Nuclear Safety Design Criteria and Explosives Safety Criteria" (Ref. B-3), and "Implementation

Guide for Use with DOE Orders 420.1 and 440.1 Fire Safety Program" (Ref. B-4) which are

intended to assure acceptable performace of DOE facilities in the event of earthquake,

wind/tornado, and flood hazards. As discussed in Chapter 1, performance is measured by target

performance goals expressed as an annual probability of exceedance of acceptable behavior

limits (i.e., behavior limits beyond which damage/failure is unacceptable). DOE O 420.1 and the

associated Guides establishes a graded approach for NPH requirements by defining performance

categories (numbered 0 through 4) each with a qualitative performance goal for behavior (i.e.,

maintain structural integrity, maintain ability to function, maintain confinement of hazardous

materials) and a qualitative target probabilistic performance goal. DOE-STD-1020 provides four

sets of NPH design and evaluation criteria (explicit criteria are not needed for Performance

Category 0). These criteria range from those provided by model building codes for Performance

Category 1 to those approaching nuclear power plant criteria for Performance Category 4.

DOE-STD-1020 employs the graded approach by following the philosophy of

probabilistic performance goal-based design and evaluation criteria for natural phenomena

hazards. Target performance goals range from low probability of NPH-induced damage/failure

to very high confidence of extremely low probability of NPH-induced damage/failure. In this

manner, structures, systems, and components (SSCs) are governed by NPH criteria which are

appropriate for the potential impact on safety, mission, and cost of those SSCs. For example, a

much higher likelihood of damage would be acceptable for an unoccupied storage building of

low value than for a high-occupancy facility or a facility containing hazardous materials. SSCs

containing hazardous materials which, in the event of damage, threaten public safety or the

environment, and/or which have been determined to require special consideration, should have a

very low probability of damage due to natural phenomena hazards (i.e., much lower probability

of damage than would exist from the use of model building code design and evaluation

procedures). For ordinary SSCs of relatively low cost, there is typically no need or requirement

to add conservatism to the design beyond that of model building codes. For these SSCs, it is also

typically not cost-effective to strengthen structures more than required by model building codes

that consider extreme loads due to natural phenomena hazards.

Performance goals correspond to probabilities of structure or equipment damage due to

natural phenomena hazards; they do not extend to consequences beyond structure or equipment

damage. The annual probability of exceedance of SSC damage as a result of natural phenomena

B-1