Salt water cooling has already been used for the large graphite-moderated thermal reactors of Britain which are situated mainly on coastal sites. Good condensing temperatures are obtained but the corrosion problems make the use of salt water more expensive than fresh water.

It has been suggested that the very slight temperature rise of the sea which results could be put to good use in keeping northern channels free from ice, in lengthening the lobster season in Maine, in allowing fish herding in Long Island Sound, or even in increasing the numbers of tropical fish in the south. Additional uses include warming recreational waters (10). However, adverse effects have been suggested that change existing fish populations. Thus limits are placed on temperature changes by the Federal Water Pollution Control Administration. In coastal or estuarine waters, the discharge of heated waste should raise the maximum daily temperature on a monthly mean basis no more than 4°F during fall, winter, and spring, and no more than 1.5°F during the summer.

Once-through cooling from rivers is the most economical cooling method and was the usual method applied in the past. For large plants, depending on the size of the river, temperature changes could be fairly large. The Vermont Yankee based on the Connecticut river might have raised the temperature at the river discharge by about 20°F (10). Such a change of river temperature would change the present ecological balance and result in a new balance with different fish and different plant groups. Such a change would most likely be an undesirable one although research is not complete on the exact effect that would be obtained (9a), and the undesirability has not yet been demonstrated. The limitations now set on rises in river tempe­ratures are set by each state and they range below 10°F depending on the value of the temperature at any time (11).

Fresh water circulated through a power plant’s condensers from cooling ponds or lakes with subsequent ejection to the atmosphere by radiation and convection is attractive, since the water is used over and over again in a self-contained system. The method appears to be economical.

The rejection of heat for other applications such as heating apartment buildings or even whole towns (10) has been practiced in local areas, but the method cannot be considered an overall solution for the rejection of excess heat, especially since many power plants are situated in relatively remote areas.

There are different types of cooling towers. The main division is between the wet evaporative kind, in which some of the cooling water is evaporated to remove heat, and the dry kind, in which a tubed radiator transfers heat. Both kinds can employ natural draft cooling or induced draft cooling. They are designed broadly to lower the temperature of the cooling water by about 15-17°F. Which kind is used in a particular application depends on the natural climate and its effect on the possibility of natural draft, the surround­ing countryside, and the effect of physically obtrusive structures, and whether or not it is necessary to avoid the use of noisy blowers for induced draft versions.

The advantage of cooling towers is mainly that they are a method of cooling recirculating water by direct contact with the environment rather than through the medium of a river. An additional advantage is that although they are very tall, cooling towers occupy relatively little site area when compared to cooling ponds which may occupy hundreds of acres of land area.

In siting any reactor plant, including a fast reactor installation, a com­prehensive assessment of the impact of cooling upon the environment is now a necessity and the AEC, as the licensing authority, now has the power to refer applications for plant licenses to agencies having legal jurisdiction in environmental matters and to require that the licensee observe certain applicable environmental limits. This extension of the AEC powers was enacted in 1969 (12).