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The Thorium

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 titanic1    244

Thorium is more abundant in nature than uranium.
It is fertile rather than fissile, and can only be used as a fuel in conjunction with a fissile material such as recycled plutonium.
Thorium fuels can breed fissile uranium-233 to be used in various kinds of nuclear reactors.
Molten salt reactors are well suited to thorium fuel, as normal fuel fabrication is avoided.
The use of thorium as a new primary energy source has been a tantalizing prospect for many years. Extracting its latent energy value in a cost-effective manner remains a challenge, and will require considerable R&D investment. This is occurring preeminently in China, with modest US support.Nature and sources of thoriumThorium is a naturally-occurring, slightly radioactive metal discovered in 1828 by the Swedish chemist Jons Jakob Berzelius, who named it after Thor, the Norse god of thunder. It is found in small amounts in most rocks and soils, where it is about three times more abundant than uranium. Soil contains an average of around 6 parts per million (ppm) of thorium. Thorium is very insoluble, which is why it is plentiful in sands but not in seawater, in contrast to uranium.Thorium exists in nature in a single isotopic form – Th-232 – which decays very slowly (its half-life is about three times the age of the Earth). The decay chains of natural thorium and uranium give rise to minute traces of Th-228, Th-230 and Th-234, but the presence of these in mass terms is negligible. It decays eventually to lead-208.When pure, thorium is a silvery white metal that retains its lustre for several months. However, when it is contaminated with the oxide, thorium slowly tarnishes in air, becoming grey and eventually black. When heated in air, thorium metal ignites and burns brilliantly with a white light. Thorium oxide (ThO2), also called thoria, has one of the highest melting points of all oxides (3300°C) and so it has found applications in light bulb elements, lantern mantles, arc-light lamps, welding electrodes and heat-resistant ceramics. Glass containing thorium oxide has both a high refractive index and wavelength dispersion, and is used in high quality lenses for cameras and scientific instruments.Thorium oxide (ThO2) is relatively inert and does not oxidise further, unlike UO2. It has higher thermal conductivity and lower thermal expansion than UO2, as well as a much higher melting point. In nuclear fuel, fission gas release is much lower than in UO2.The most common source of thorium is the rare earth phosphate mineral, monazite, which contains up to about 12% thorium phosphate, but 6-7% on average. Monazite is found in igneous and other rocks but the richest concentrations are in placer deposits, concentrated by wave and current action with other heavy minerals. World monazite resources are estimated to be about 16 million tonnes, 12 Mt of which are in heavy mineral sands deposits on the south and east coasts of India. There are substantial deposits in several other countries (see Table below). Thorium recovery from monazite usually involves leaching with sodium hydroxide at 140°C followed by a complex process to precipitate pure ThO2. Thorite (ThSiO4) is another common thorium mineral. A large vein deposit of thorium and rare earth metals is in Idaho.


Atomic Number: 90
Atomic Symbol: Th
Atomic Weight: 232
Melting Point: 3,182 F (1,750 C)
Boiling Point: 8,650 F (4,788 C)

Word origin: Thorium is named for Thor, the Norse god of thunder.

Discovery: Thorium was discovered as an element in 1928 by Swedish chemist Jons Jakob Berzelius. Berzelius received a sample of an unidentified black mineral from mineralogist Jens Esmark, whose son Morten Esmark had found it on Lovoya Island, Norway. Esmark suspected it contained an unknown substance. His mineral is now known as thorite.

Properties of thorium

Thorium is radioactive and decays at a fixed rate into a series of other elements. In its pure state, thorium is a silvery-white metal that is stable in air and retains its luster for several months. If contaminated with oxide, however, it tarnishes slowly in air. It turns gray and eventually black. [See Periodic Table of the Elements]

Thorium’s physical properties are strongly influenced by how much it is contaminated with oxide. Even the purest specimens of thorium often contain several tenths of a percent of oxide. Thorium oxide has a melting point of 3,300 C (5,972 F), the highest of all the oxides.

Pure thorium is soft, very ductile, and can be swaged, drawn and cold-rolled. When heated in air, its turnings ignite and burn with a brilliantly white light. Powdered thorium is pyrophoric, requiring careful handling.

Thorium is dimorphic, changing from a cubic to a body-centered cubic structure at 1,400 C (2,552 F). Thorium does not dissolve easily in most common acids (with the exception of hydrochloric) but water slowly attacks it.

Much of the earth’s internally produced heat is attributed to thorium and uranium.


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