ABSTRACT
While the considerations listed above continue to be valid, the nuclear disaster, which took place in Fukushima, Japan, on Mar. 11, 2011, raised grave doubts among the countries whether the benefits of nuclear power are worth the cost in human misery and economic destruction when nuclear accidents happen. Germany has chosen to forego the nuclear option altogether. In France, there is a talk of reducing the country’s dependence on nuclear power from the current 75% to 50% by 2025. The EPR plant under construction in Flamanville, France, has seen long delays and massive cost hikes. A recent accident in the oldest nuclear site in Marcule further undermined the image of the French nuclear industry, though the French Government took great pains to
describe it as an industrial accident rather than a radiological accident. No wonder, India has reportedly informed France that it will import French reactors only after post-Fukushima certification. Only fissile isotopes can be used directly in nuclear fission for generating power.
Fertile isotopes have to be rendered fissile first, before being used to produce nuclear fission. Uranium has two isotopes – fissile isotope 235U with an abundance of about 0.7%, and fertile isotope 238Uwith an abundance of about 99.3%. Neutron absorption in 238U produces the fissile plutonium isotope, 239Pu. On the other hand, thorium has no fissile isotope, but consists entirely of fertile isotope 232Thwhich has to be converted to fissile 233U through neutron absorption before being used for nuclear fission. 233U produces themost neutrons per neutron absorption at thermal energies (slow neutrons) and is hence superior to both 235U and 239Pu as nuclear fuel in the common light water thermal reactors. Enriched uranium fuel, which is used in the reactors, is produced by enriching the
235U content to 4-5%. 233U does not occur in nature – it has to be “bred’’ (hence the term, breeder reactors). Enriched uranium (typically, 20% 235U) or 239Pu is needed for the start-up of such reactors. When thorium is substituted for natural uranium in a breeder reactor, as much (or more) 233U is produced by neutron absorption in thorium, as is consumed in the reactor operation. Also, when once the reactor is started, no further enriched uranium is needed. Power reactors: The fissioning of one kg of 235U yields 22.66×106 kWh of energy,
equivalent to 2750 t of bituminous coal. The fuel value of one ton of uranium is 6.8×1013 BTU. The very high fuel value of uranium has profound implication for siting the nuclear power plants. While coal-fired thermal power stations have to be established at pithead in order to save on transportation costs, and hydroelectric power stations have to be set up at dam site, a nuclear power station is not subject to such constraints (a 1000MWe power station would need annually about 3.1 million tonnes of hard coal, but only about 24 tonnes of enriched uranium).
