Hazard Analysis Results cont'd - DOE-STD-1120-1-20050024

DOE-STD-1120-2005/Vol. 1

seismic response is affected by reduction in structural load capacity). Additionally,

decommissioning may introduce activities that were not addressed in the previous DSA. The

impact of any new activities on the existing NPH evaluation should also be considered when

determining if the existing evaluation is adequate for decommissioning operations. Where such

an evaluation does not exist or is less than adequate, conservative assumptions can be made in

the decommissioning DSA without the need for further NPH analysis.

Any NPH evaluation performed in support of decommissioning should be inclusive of all

applicable natural phenomena, and should be sufficient to allow DOE to understand potential

consequences to workers, the public, and environment. Typically, very qualitative evaluations

should be sufficient, given that facilities undergoing decommissioning have a short remaining

life when compared to the facility's operational phase, and material at risk is being constantly

reduced with a resultant reduction in consequences from postulated NPH accident events. For

instance, in a seismic scenario, a worst case assumption that the building will collapse may be

made in lieu of detailed seismic response calculations. In this case, the consequences of the

building collapse may be acceptable to DOE, provided appropriate controls such as emergency

plans/procedures are clearly understood and referenced in the DSA. The facility undergoing

decommissioning will still be required to meet 29 CFR 1926 to protect life safety during work

activities that require habitation of the facility, but will not be required to meet the performance

criteria indicated by DOE-STD-1020.

Other external low probability, high consequence events (e.g., aircraft crash) may be treated

similar to NPH events as described above (i.e, use of previous analysis, qualitative evaluation,

etc). Some external events may present a higher probability of occurrence during

decommissioning such as external vehicle impacts as a result of heavy equipment, or increased

waste transportation activities.

During decommissioning activities within a facility, administrative processes and safety

management programs normally are of utmost importance for protecting workers from hazards.

However, there are times when active and passive safety SSCs are necessary until certain

hazards are eliminated. An example of such an SSC would be the criticality accident alarm

system at facilities that still have fissile material present in sufficient quantities that a criticality

hazard exists.

For operating facilities, the ability of the Safety SSC to survive DBAs from NPH events would

need to be demonstrated through analysis and documented in the SSC's system evaluation (see

Chapter 4 of STD-3009 and DOE O 420.1A 4.4). In the case of decommissioning, the SSC may

not be capable of surviving NPH DBAs. Where NPH analysis is not available from the previous

DSA to demonstrate NPH qualification, or where facility modifications may invalidate the

qualification, failure of the Safety SSC can be assumed rather than performing further NPH

analysis.

A priority should be placed on expediently reducing the hazards and risks to the point where the

SSC is no longer required. Consideration should also be given to establishing post-NPH event

procedures that ensure the Safety SSC is still capable of performing its' safety function

following NPH events that may be of lesser magnitude and higher frequency than DBAs. When

3-7