om 40 to Sum mak process is ng is gene fuel froc rate half! been developed to predict the environmental concentrations and exposures which may result from a given release rate. The most widely used empirical relation to measure short-range effects is that of Sutton for an elevated point source: 5 ertain a during ystems released contam ction, an sion pro terials of na decor merates r where: X(x,y)=concentration at ground level at point (x,y), units/m3 Q=emission rate, units/sec u= wind speed, m/sec x=distance downwind, m y=crosswind distance from plume axis, m Cu, C2 virtual diffusion coefficients in y and z directions, (m)/2 n-wind-profile parameter, dimensionless 6 Two important derivations can be calculated from Eq. 6.1: the maximum concentration at ground level downwind and the location of the point of maximum ground-level concentration. These relations are herefore thods pri of fixing liquids. and Then sat calcina ation. ypton, Jet lium, cest krypton ma expos elease pl for inhala hreat is fr in the t ats in inhal is immers ugh accur of the fo ethod of b mations b The applicability of these equations to a given situation depends upon the proper choice of values for n, C, and C2, the distance to which concentrations are predicted, and the topography of the surface over which the release travels. Empirical verification of the Sutton diffusion theories has been made only to a distance of from 3 to 5 miles. Extrapolation to greater distances is difficult for a number of reasons. Important among them is the degree to which meteorological conditions along the trajectory vary from the one-point conditions utilized in the original calculations. Calculations of these and other relations derived from Sutton's equations have been simplified in a series of nomograms published in Meteorology and Atomic Energy. The effect of lapse and inversion conditions on the values of Xmax. and Imax. are shown when typical values for the parameters n, Cy, and C2, suggested by Smith and Singer for these conditions, are substituted in Eqs. 6.2 and 6.3. The values obtained are given in Table 6.1 in terms of the specified parameters. The calculations show that under inversion conditions the maximum concentration, Xmax., has been lowered by a factor of 8 and that the point of maximum concentration, max., has been moved a distance about 50 times farther TABLE 6.1-VALUES OF Xmax. AND Xmax. CALCULATED FOR SPEC from the source. Application of the equations in this way ass constant meteorological conditions over an extended area and o period of time. These assumptions may not be warranted, caution should be used when applying the equations. These equations have been modified for application to the trans of airborne particulates since gravity forces must be taken consideration.8,9 Local weather data (micrometeorology) can provide inform that is extremely useful in estimating dilution capacity of air m for specific releases of radioactive airborne wastes. They are neces for estimating ground concentration levels under specific condi of release, for determining necessary stack height, for locating exhausts and intakes, and for determining building layout in t of prevailing wind direction. Information also is needed on pre tation and accompanying wind direction to evaluate washou contaminants. Finally, meteorological data are extremely he in locating suitable sample collection stations. Although geogra and topography affect the dilution efficiency of the atmosphere, cannot be measured in terms used in the determination of atmosp diffusion. In practice, only wind vectors and temperature gradi can be measured with ease. 6-3 DIFFUSION MECHANICS The change in temperature with height above the ground is vertical temperature gradient. For diffusion predictions the perature profile for the first few thousand feet is often required, bu practice, the profile up to stack height is usually all that is avail The vertical temperature gradient may be either positive or nega When the temperature decreases with altitude, a lapse cond is said to exist; when it increases with altitude, an inversion ex When there is no change in temperature with altitude, an isothe condition exists. The temperature of an air parcel that is mechanically displ varies at the adiabatic temperature gradient of 0.5°F per 10 ground is ons the te quired, bu at is avail ve or negat pse condi version er an isother When a lapse condition prevails where the temperature decreases by more than 0.5°F per 100 ft (dry adiabatic), the conditions are unstable, and a displaced air parcel continues to be displaced by buoyancy forces. When an inversion exists, the surrounding air has a higher temperature than the displaced air parcel, and buoyancy forces resist further displacement. In addition to the effects of diffusion, which can be estimated by the empirical relation previously mentioned, there are other conditions that must be considered in the establishment of safe stack-discharge levels. During periods of strong vertical currents (good diffusion conditions), it is possible for the entire plume to be whipped down to the ground with little dilution (looping). This would deliver a ground concentration several orders of magnitude higher than predicted by the Sutton equations. A second important condition is that of fumigation, which describes the downward-to-the-ground mixing of effluent material that has accumulated aloft during a period of thermal stability. Fumigation occurs most commonly after dawn, when the nocturnal ground temperature is raised by the sun. Equations to evaluate this effect have been developed by Holland1o and Lowry.11 Environmental radioactivity levels should be determined to confirm the validity of estimates made with the empirical equations cited earlier. It is only in this way that areas of high concentration influenced by the local terrain and weather conditions can be isolated and their effects evaluated. Comparison with previous results is also important to detect changes in the concentration pattern resulting from the addition of new buildings, modifications of topography, and particularly the introduction of new sources of contamination. Model studies either in wind tunnels or with simulated effluents can have value in predicting the movement of contaminated air parcels under a wide variety of meteorological conditions. Such studies are helpful in planning the location of sampling stations for the collection and measurement of surface concentrations, and they are useful in determining the height and location of the stack through which radioactive and other contaminants can be released to the environment. 6-4 ENVIRONMENTAL EVALUATION Chapter 1 states that the International Commission on Radiological Protection (ICRP)12 and the National Committee on Radiation Protection (NCRP) have recommended maximum permissible concentrations for radionuclides in air and water for occupational exposure and have applied specific factors to these values for application to population groups. In a similar manner the Federal Radiation + Council (FRC) has developed guidance on radiation exposur federal agency use. 13,14 Permissible radionuclide levels in air re mended by the NCRP for a selected list of radionuclides are list Table 6.2. TABLE 6.2-MAXIMUM PERMISSIBLE CONCENTRATIONS (168-HR + *In addition to the conventional MPC values, expressed as microcuries per milliliter, a compa measure of toxicity, pMPC, is introduced. This quantity, which is analogous to pH in that it is as the negative logarithm of the concentration (expressed in microcuries per milliliter) is offered as venient unit with the advantages of eliminating the exponential notation and of using a larger, rathe smaller, number for the more toxic nuclides.15 Lower large intestine. Because the general population is currently exposed to a complicated mixture of radionuclides and because radioactive wastes are generally a mixture of several radionuclides, a listing of the relative hazards of specific nuclides is inadequate to evalute the public-health hazard of the nuclear industry. The guides that have been developed suggest methods of weighting the recommended levels when two or more radionuclides that affect the same critical organ are observed. This computation can become quite complex and reference to NBS Handbook 69 is suggested for those concerned with such determinations.* Table 4 of NBS Handbook 69 (reproduced as Table 6.3 in this chapter) establishes acceptable guides for unidentified or partially identified mixtures. These guides should be applied with as complete a knowledge of the nuclides as possible. When such knowledge is not available, the limit must be set as though the aerosol consisted entirely of the most-toxic contaminant possible even though its major component might actually be a less-toxic nuclide and less rigorous restrictions could be used. TABLE 6.3-PROVISIONAL MAXIMUM PERMISSIBLE CONCENTRA- Limitations If there are no a emitters and if ẞ emitter Ac227 is not present,† If Pa231, Th (natural), Pu239, Pu240, Pu242, and Cf249 are not present, † 10-12 7X10-13 4 X 10-13 *Use o of these values for interim application in the neighborhood of an atomic energy plant. Experience has shown that the most-toxic radionuclides are not always the most hazardous. Other nuclides because of their abun If there are no a emitters and if ß emitters Pb210, Ac227, Ra228, and If there are no a emitters and if ẞ emitters Sr90, I129, Pb210, Ac227, μc/cc of air* 10-9 10-10 10-11 |