In the United States about 80 quads (1 quad = 10 15 Btu) or about 84 x 10¹⁵ kJ of energy is consumed each year. Approximately one-fourth of this energy is transformed into electricity and, on the average, about 3 units of energy are needed per unit of electricity.

(a) If all the energy were derived from coal, and each ton of coal makes available 25 x 10⁶ kJ, what would be the amount of coal consumed per year?

(b) If all the U.S. energy consumption were to be supplied in the form of electricity, the electricity were produced from fissioning of uranium 235, and the amount of natural uranium used is about 200 times the amount of the fissioning isotope 235, what would be the annual amount of natural uranium that must be used? Recall that the fission of each atom of uranium 235 yields about 200 MeV or, equivalently, 1 MW day/g.