An abundant supply of thorium is necessary to implement thorium-based fuel cycles on a scale necessary to significantly supplement uranium resources. Thorium, which is essentially 100% ²³²Th, is three times more abundant in the earth’s crust than uranium, reflecting the differences in the half-lives of ²³²Th (1.4x10¹⁰ years) and ²³⁸U (4.5x10⁹ years).

Thorium is easily obtainable, with monazite sand being the most common and commercially most important thorium-bearing mineral. The Encyclopedia of Science and Technology says that the energy available from the world’s supply of thorium has been estimated as greater than the energy available from all of the world’s uranium, coal, and oil combined, and the system of ²³²Th/²³³U gives promise of complete utilization of all thorium in the production of atomic power.

Economically extractable world thorium reserves—primarily in monazite—equal approximately 1.2 million tons, with monazite resource distribution per country as shown in the following table:

Thorium occurs in various minerals and is found in small amounts in most rocks and soils, which commonly contain an average of around six parts per million of thorium. Thorium occurs in diverse rock types. It occurs as veins of thorite/uranothorite and monazite in granites, syenites, and pegmatites. Moreover thorium occurs in bastnaesite and carbonatites.

Uranium Locations:  Large-scale uranium mining began in the southwestern United States during World War II as a result of the nuclear weapons development program. At that time, the only known deposits of uranium were located in Canada and the Congo, and these deposits were almost depleted. Because uranium was known to occur with vanadium, the search for new sources of uranium to support the nuclear weapons program focused on the tailings piles of vanadium mills and around the sites of vanadium mines, located primarily on the Colorado Plateau, a large region in the Four Corners area of New Mexico, Colorado, Utah, and Arizona. Nearly 90% of U.S. uranium resources and current production are centered in this region. The actual presence of uranium may be verified by chemical and/or radiological testing. Uranium ore in the western states is contained in quartz sandstone, where typical deposits assay at 0.20-0.25 wt% (weight percent) uranium metal.