Table 6.3 lists the power conversion efficiencies for nuclear and fossil — fueled plants. It can be seen that something over 60% of the heat produced within a power plant is in excess of that which can be used in creating electricity. This inefficiency is suffered by all heat machines and the thermal nuclear plants, at present using lower temperature steam, are somewhat more inefficient than the fossil-fueled systems. However, the difference is

not significant and, size for size, the thermal effects of these competing systems are the same in magnitude. Fast reactors will eventually be capable of higher efficiencies in the large sizes. However, about 25% of the excess heat from a fossil-fueled plant is discharged directly from its stack along with gaseous pollutants; therefore the amount of excess heat to be removed by cooling water is relatively less than for the light-water-cooled nuclear plants. With fast reactors, however, the amount of heat released to the cooling water by the nuclear and fossil plants will be much the same (9a).

To put the excess heat position in perspective, by the year 2000, approx­imately 1250 billion gallons of water per day will be required to remove excess heat. About 30% of this will be discharged to the sea and the remain­der will require surface runoff water in some form for cooling. Since the total average daily runoff for the United States is about 1200 billion gallons, over 70% of this would be required to cool the power plants in existence at that time, or at least to transfer the excess heat to the ultimate heat sink of the atmosphere (9b).