Evaluation of Existing Facilities - Continued

DOE-STD-1020-2002

existing SSCs is similar to evaluations performed of new designs except that a single as-is

configuration is evaluated instead of several configurations in an iterative manner, as required in

the design process. Evaluations should be conducted in order of priority, with highest priority

given to those areas identified as weak links by preliminary investigations and to areas that are

most important to personnel safety and operations with hazardous materials. Prioritization

criteria for evaluation and upgrade of existing DOE facilities are currently being developed.

If an existing SSC does not meet the natural phenomena hazard design/evaluation

criteria, several options (such as those illustrated by the flow diagram in Figure B-2) need to be

considered. Potential options for existing SSCs include:

Conduct a more rigorous evaluation of SSC behavior to reduce conservatism which

may have been introduced by simple techniques used for initial SSC evaluation.

Alternatively, a probabilistic assessment of the SSC might be undertaken in order to

demonstrate that the performance goals for the SSC can be met.

The SSC may be strengthened to provide resistance to natural phenomena hazard

effects that meets the NPH criteria.

The usage of the SSC may be changed so that it falls within a lower performance

category and consequently, less stringent requirements.

If SSC evaluation uncovers deficiencies or weaknesses that can be easily remedied, these should

be upgraded without considering the other options. It is often more cost-effective to implement

simple SSC upgrades than to expend effort on further analytical studies. Note that the actions in

Figure B-2 need not necessarily be accomplished in the order shown.

Evaluations of existing SSCs must follow or, at least, be measured against the NPH

criteria provided in this document. For SSCs not meeting these criteria and which cannot be

easily remedied, budgets and schedule for required strengthening must be established on a

prioritized basis. As mentioned previously, prioritization criteria for evaluation and upgrade of

existing DOE facilities are currently being developed. Priorities should be established on the

basis of performance category, cost of strengthening, and margin between as-is SSC capacity and

the capacity required by the criteria. For SSCs which are close to meeting criteria, it is probably

not cost effective to strengthen the SSC in order to obtain a small reduction in risk. As a result,

some relief in the criteria is allowed for evaluation of existing SSCs. It is permissible to perform

such evaluations using natural phenomena hazard exceedance probability of twice the value

specified for new design. For example, if the natural phenomena hazard annual probability of

exceedance for the SSC under consideration was 10-4, it would be acceptable to reconsider the

SSC at hazard annual probability of exceedance of 2x10-4. This would have the effect of slightly

reducing the seismic, wind, and flood loads in the SSC evaluation. Where it is not practical to

undertake analysis based on double the probability, no more than 20% reduction in forces may

be permissible. This amount of relief is within the tolerance of meeting the target performance

goals and is only a minor adjustment of the corresponding NPH design and evaluation criteria.

B-8