Thorium has always been an alternative to uranium for fueling nuclear reactors, but it hasn’t gotten much play. That may soon change. According to a report by Doug L. Hoffman at Resilient Earth, the Norwegian government and Westinghouse are beginning a five-year experiment to test thorium as a fuel for the reactors. Read that post for details. The thorium cycle is shown in the graphic below:
Thorium has some advantages over uranium: it is more abundant; it produces less toxic waste products, and its by-products cannot be used in weapons. Thorium reactors can also burn up existing nuclear waste.
According to Hoffman, “If thorium is so fantastic why isn’t it in wide use already? There have been prototype reactors built in the past. A pair of reactors operated in Germany between 1983 and 1989, and three operated in the US between the late sixties and early eighties. Alas, all of these plants were abandoned. In the US, the military was not interested in ‘safe’ atomic reactors, they wanted the enriched uranium and plutonium produced by uranium fueled reactors for use in weapons. The world’s largest consumer of civilian nuclear power turned its back on thorium because it did not produce dangerous enough waste products.”
Let’s now turn to geology to see where thorium comes from. A good overview is in USGS Circular 1336: “Thorium deposits of the United States.”
“Thorium minerals occur in alkaline igneous rocks and carbonatites, but the most concentrated deposits occur in epigenetic veins that surround alkaline igneous complexes. Thorium’s genetic association with alkaline igneous rocks also places thorium in close association with minerals that host other valuable elements, such as those containing rare earth elements (REE), titanium, niobium, and phosphorus. Large titanium deposits can exist in the ultramafic units of the alkaline igneous complex. In addition to metallic resources, many of the rock units of these alkaline complexes, such as nepheline syenite and carbonatite (an apatite source), can have industrial mineral uses in their raw crushed form.”
The principal thorium minerals are: Monazite (Ce,La,Y,Th)PO4, Thorite (Th,U)SiO4, Brockite (Ca,Th,Ce)(PO4) H2O, Xenotime (Y,Th)PO4, and Euxenite (Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6.
The map below shows known sources of thorium in the United States. The two largest deposits are Lemhi Pass district of Montana-Idaho and the Wet Mountains area of Colorado.
Thorium has been tried before. One technology was the liquid thorium fuel reactor with molten salt coolant for which interest is re-emerging as a potentially safe, cost-effective energy source. If the Norwegian experiment is encouraging, we will have another energy source, one with the advantage of also providing the increasingly important rare earth minerals also.