Accelerated growth of nuclear power in different countries foreseen in future, due to increased demand of carbon-free energy, has made the sustainable use of fuel metals such as uranium and thorium important. While uranium is the main-stay of the present generation of NPPs, with the anticipated steep growth in nuclear energy in future, it will be necessary to introduce thorium too as a fuel.
It is generally believed that thorium resources should be 3 to 4 times larger than uranium resources because the Clarke concentration of thorium is 3 to 4 times larger than that of uranium. However, such a statement does not take into account the differences of chemical properties between uranium and thorium. Uranium has two valence states U4+ and U6+, and is very soluble, as UO22+ under oxidized state. Thorium has only one valence state, Th4+, and has a low solubility at low to intermediate temperature. This property has several major consequences:
- Thorium minerals can be concentrated physically in placer type deposits as resistates;
- Most other thorium deposit types are formed in magmatic and high temperature hydrothermal environments; and
- Metallurgical extraction of thorium from ores requires more costly processes than for U.