Atmospheric Dispersion Analysis using MACCS2

The Nuclear Regulatory Commission (NRC) Regulatory Guide 1.145 requires an evaluation of the offsite atmospheric dispersion coefficient, {Chi}/Q, as a part of the acceptance criteria in the accident analysis. In it, it requires in sequence computations of (1) the overall site 95th percentile {Chi}/Q, (2) the maximum of the sixteen sector 99.5th percentile {Chi}/Q, and (3) comparison and selection of the worst of the two values for reporting in the safety analysis report (SAR). In all cases, the site-specific meteorology and sector-specific site boundary distances are employed in the evaluation. There are sixteen 22.5-sectors, the nearest site boundary of which is determined within the 45-arc centered on each of the sixteen compass directions.