Key Difference – Thorium vs Uranium
Both Thorium and Uranium are two chemical elements from actinide group, which have radioactive properties and function as energy sources in nuclear power plants; the key difference between Thorium and Uranium exists in their natural abundance. Thorium is three times more abundant than Uranium in the Earth’s crust. This is due to its longer half-life than that of Uranium. In addition, Thorium is present in larger quantities (about 2%-10%), while Uranium is present in smaller quantities (about 0.1%-1%) in natural ores.
What is Thorium?
Thorium is a weakly radioactive chemical element from actinide series with symbol Th and atomic number 90. Not many radioactive elements naturally occur in larger quantities; Thorium is one of the chemical elements which naturally occurs in great quantities. The other two radioactive elements are Bismuth and Uranium. Thorium has six known unstable isotopes and 232Th has the longest life.
Compared to Uranium, Thorium is a greater energy source. It is estimated that the nuclear energy available in Thorium is greater than the energy that can be obtained from oil, coal and Uranium. The main reason for not developing many Thorium nuclear reactors is that it requires a large capital investment for the process, and its breeding process is slow. To avoid these issues, a combination of Uranium and Thorium is used in nuclear reactors as the initial start-up fuel source. 
What is Uranium?
Uranium is a silvery-white metal, and it is a chemical element in the actinide group of the periodic table. Its symbol is U and the atomic number is 92. Uranium has three major isotopes (U-238, U-235 and U-234); all of them are radioactive. Therefore, Uranium is considered as a radioactive element. The molecular weight of Uranium is 238 gmol-1, which is considered as the heaviest naturally occurring element on the earth. It is naturally present in smaller quantities in the soil, water, rocks, plants and the human body.
Uranium is the main energy source in commercial nuclear power plants. Uranium can produce a significant amount of energy, after the enrichment process. The energy produced by one kilogram of Uranium is equivalent to energy produces from 1500 tons of coal. Therefore, Uranium is one of the major energy sources in nuclear power plants. For industrial uses, about 90% of Uranium comes from five countries; Canada, Australia, Kazakhstan, Russia, Namibia Niger, and Uzbekistan.
What is the difference between Thorium and Uranium?
Appearance & Natural Abundance of Thorium and Uranium
Thorium: Thorium is a silvery-white metal, which tarnishes when exposed to the air. Thorium is present in larger quantities (2%-10%) in its natural ores.
Uranium: The refined Uranium is silvery white or silvery gray metallic color. Uranium is present in very smaller quantities (0.1%-1%) and, therefore, it is less abundant than Thorium.
Radioactive Properties of Thorium and Uranium
Thorium: Thorium is a radioactive chemical element; it has six known isotopes, they are all unstable. However, 232Th is comparatively stable, with a half-life of 14.05 billion years.
Uranium: Uranium has three main radioactive elements; in other words their nuclei spontaneously disintegrate or decay. U-238 is the most abundant isotope. Unlike Thorium, some of Uranium isotopes undergo fission.
| Isotopes | Half-life | Natural abundance |
| U-235 | 248 000 years | 0.0055% |
| U-236 | 700 million years | 0.72% |
| U-238 | 4.5 billion years | 99.27% |
Uses of Thorium and Uranium
Thorium: The use of as an energy source in nuclear reactors is one of the main uses of Uranium. In addition, it is used in producing metal alloys and was used as the light source in gas mantles. But, these mentioned uses declined due to its radioactivity.
Uranium: The main use of Uranium is its function as fuel in nuclear power plants. In addition, Uranium is also used in nuclear weaponry to produce atomic bombs.
Image Courtesy: “Electron shell 090 thorium”. (CC BY-SA 2.0 uk) via Wikimedia Commons “Electron shell 092 Uranium”.(CC BY-SA 2.0 uk) via Wikimedia Commons
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