Meteorological design basis

The design basis flood for a given site may result not from the occurrence of one extreme event but from the simultaneous occurrences of more than one severe event each of which is in itself less than the extreme event. The interdependence or independence of the potential flood causing phenomena should be examined according to the site specificity. In many combinations of flood causing events the distinction between dependent and independent events is not sharp. Sequential meteorological events, for example, are only partially dependent on or fuUy independent of each other. In contrast, seismic and wind events are clearly independent. 

The potential doses at the exclusion area boundary and the low population zone are calculated assuming that the accident occurs when the meteorological conditions are worse (from the standpoint of the calculated doses) than those that would be expected to prevail at the site approximately 95% of the time [Regulatory Guides 1.3 and 1.4]. Table 2.1-4 presents the results from typical calculations of potential offsite doses due to several kinds of design basis accidents. Even with the considerable number of pessimistic assumption employed, the calculated doses that a person out-of-doors in the vicinity of the plant might receive for the entire course of the accident are usually well below the 10 CFR Part 100 guidelines. 

If more sophisticated investigations and analysis are necessary, NUSS Safety Guides 50-SG-SllA, "Extreme Meteorological Events in Nuclear Power Plant Siting, Excluding Tropical Cyclones" [11) and 50-SG-SllB "Design Basis Tropical Cyclone for Nuclear Power Plants" (12) can be referred to. 

Prior to the previous nuclear testing at the NTS, analysis was made of the meteorology for the area. This was critical in the original selection of the site, and continued collection of atmospheric data has allowed prediction of specific meteorological conditions that are hard to capture on any other site on a reliable basis. This is particular important when designing instrument arrays to capture dispersion clouds or specific atmospheric conditions. 

During storms, the first water to fall washes the ground and is the most polluted. The flow may be from 500 to 3000 m -h Since it is not feasible to treat this amount at its instantaneous flow rate, the water must be stored in a storm basin designed on the basis of historical meteorological statistics. 

On the basis that these eriteria are site specific and not strategic, they have been excluded and will not be discussed further at this stage of the GDA process. It should be noted, however, that some issues e. g. seismic risk and meteorology have been discussed briefly in this chapter with regard to the generic APIOOO design. 

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