The dispersion depends critically on wind conditions and the stack height h from which the emission takes place. The basic dispersion equation is

X(x, y, 0) = (Q/novozH) exp[—(h2/2az2) — (y2/2ov2)] (5.5)

where x is the concentration on the ground at (x, y) (Ci/m3); Q is the release rate (Сі/sec); ay, az are the crosswind and vertical plume standard devia­tions (m); й is the mean wind speed at the height of the stack h (m/sec); and x, у are the downwind and crosswind position of the point of interest relative to the stack base (m). In Eq. (5.5) the crosswind and vertical plume standard deviations are both functions of the wind conditions and are therefore tabulated as a function of the Pasquill classification. Thus from this equation the wind dispersive factor xlQ таУ be calculated for insertion into the calculation of the dose by Eq. (5.2).

For a ground concentration directly downwind of the elevated source Eq. (5.5) becomes

X(x, 0, 0) = (Q/nayazu) exp(— h22l2az) (5.6)

Standard tables (13) are available for the plume standard deviations, but the actual calculation is complicated by the necessity of considering different wind conditions existing for different times. Table 6.1 details assumed wind conditions for calculations performed on the Indian Point 2 reactor plant. These conditions include allowance for building wake correction, plume meander, and various Pasquill type winds (C, D, and F) during the total time of 30 days. They give an idea of the various factors which must be included in the calculation. The set of conditions detailed in Table 6.1 are standard comparative data for PWR’s rather than a set of data for the Indian Point site. They are standards set by the AEC’s division of reactor licensing for use in comparative assessments.