The principal fossil fuels, bituminous coal, natural gases, and oil, give off a variety of pollutants that include carbon monoxide, oxides of sulfur and nitrogen, hydrocarbons, and particulate matter. Of these, sulfur dioxide is the most critical.

Oil and gas also give rise to large quantities of nitrogen dioxide, while coal and oil contribute fly ash particulates. The exposure to these pollutants is measured in an individual by the action on his lungs, and in some cases, standards apply which limit the concentration of the pollutants in the air.

To place the emission of fossil-fuel pollutants in perspective, it is worth noting (13) that the discharge quantities of sulfur dioxide amount to be­tween 27 lb/MWe-yr for gas and 306,000 lb/MWe-yr for coal, with oil coming in between. These figures, when compared to the concentration standard of 0.3 parts per million, imply that a dilution of the pollutant to the required standard may need up to nearly 2-10nm3 of air/MWe-yr (see Table 6.4).

In contrast, a PWR plant may discharge 5-10-103 //Ci/MWe-yr. In order to dilute this to the concentration standard required by the AEC 10CFR20 regulations, 10-7//Ci/cm3, approximately 5-10-104m3 of air/ MWe-yr is needed. In other words, the required dilution is something greater than a million times easier for the nuclear plants.

The RBE for radium and thorium from fossil-fuel plants is much higher than for the nuclear plants’ krypton and iodine, therefore only a little radium release can have a relatively large effect. This is exhibited in Table 6.4 and also by the dose rates quoted for three power plants: Con­necticut Yankee PWR (1968) gave 1.2 • 10~e [irem/hr-MWe, Dresden I BWR(1968) gave 8.7 • 10-2 [xrem/hr-MWe, while Widows Creek fossil plant gave 3.5 • 10-5 [xrem/hr-MWe. Thus the fossil plant gave just as much radioactive emission as nuclear plants even though it relied on an 800 ft stack to dilute effluent by a factor of 100 {9b).

Fast reactors do not differ very significantly from the LWR plants al­though they do discharge less and will have no difficulty in bettering the already excellent PWR standard.

The discharge of pollutants from fossil-fueled plants is being reduced. Effective methods for the control of particulates already exist and are in use. A Dolomite system for the removal of sulfur dioxide involves using finely divided limestone in a combustion chamber {13). Following a wet scrubber treatment, using an aqueous suspension of limestone or lime particles, it is hoped that up to 80% of the sulfur may be removed. This system is now being tested on some operating power plants. Significant reductions in the nitrogen oxides will require new combustion processes; in the meantime plants are being built with taller stacks to increase the dilution factor for the remaining discharged pollutants.