We wish to produce 1.0 GJ of energy. We have to calculate and compare (a) the amount of coal needed if we wish to obtain the energy by burning coal and (b) the amount of natural uranium needed if we wish to obtain the energy by fission in a reactor. We may assume that the combustion of 1.0 kg of coal releases ; the fission of 1.0 kg of uranium in a reactor releases .

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We assume that the combustion of 1.0 kg of coal releases ; and the fission of 1.0 kg of uranium in a reactor releases .

(a)

Therefore, for producing 1.0 GJ of energy the amount of coal needed will be

.

(b)

And, the amount of uranium required for release of energy by fission in a reactor will be

The ratio of and will be