1. Thorium instead of uranium? It may well turn out that thorium is a better nuclear fuel than uranium, since it offers the advantages that: (1) it has around four times the abundance of uranium on Earth, overall; (2) practically 100% of it can be bred into the fissile nuclear fuel [sup.233]U; (3) smaller amounts of plutonium and other transuranic elements are produced than is the case from uranium fuel; (4) the thorium fuel cycle might be used to consume plutonium, thus reducing the nuclear stockpile, while converting it into useful energy. was a conference held in Chicago, in May 2013, on 5th Thorium Energy Alliance--Future of Thorium, Energy and Rare Earths. http://thoriumenergyalliance.com/index.html. Thorium (1) is a naturally occurring radioactive element, with the chemical symbol Th and an atomic number of 90. The mineral, now known as thorite, was discovered in 1828 by the Norwegian priest and mineralogist, Morten Thrane Esmark. In the same year, the element, thorium, was identified in the material by the Swedish chemist, Jons Jakob Berzelius, who named it after Thor, the Norse god of thunder. Thorium is found in soils at an average concentration of 6 parts per million (p.p.m.), and in most rocks. In higher concentrations, thorium occurs in several kinds of mineral, of which the most common is the rare earth phosphate mineral, monazite, which contains up to about 12% thorium phosphate, but 6-7% as an average. World monazite resources are estimated to be of the order of 12 million tonnes, two-thirds of which are in heavy mineral sands deposits on the south coast and east coast of India. The world total of economically extractable thorium is estimated at around 2.61 million tonnes (Table 1) (2), and Australia and the USA top the list with 489,000 and 400,000 tonnes of it, respectively. Norway has 132,000 tonnes of thorium, which adds to the large energy reserves of this country in terms of gas, oil and coal, not to mention hydropower, from which 99% of its electricity is generated. Other than negligible amounts of a few highly radioactive isotopes, thorium occurs exclusively as [sup.232]Th. Although [sup.232]Th is not fissile in itself, it can be converted to a fissile fuel in the form of [sup.233]U, via the absorption of slow neutrons. Hence, as is the case for [sup.238]U, [232]Th is fertile and may be bred into a nuclear fuel, which in the former case is [sup.239]Pu. Kirk Sorensen, a major proponent for the development of thorium power (http://energyfromthorium.com/), particularly in conjunction with the liquid fluoride reactor, LFR (also called the molten salt reactor, MSR) has offered the following (3), in regard to the essential differences between the two elements [sup.232]Th and [sup.239]Pu, as pertaining to their use in nuclear weapons or dirty bombs: There are several reasons why U-233 is unattractive for nuclear weapons. One is that it doesn't produce as many neutrons in fast fission as Pu-239. Another is that its properties in very fast fission (such as a nuclear detonation) are poorly understood. But the biggest deterrent is that U-233 is inevitably contaminated with U-232 during its formation. It is highly impractical to separate them. And U-232 has a short half-life (~80 years) and a decay chain that includes the strong gamma emitter Tl-208. A few months after the U-233 is isolated from parent materials, the decay chain of U-232 begins to set up and the strong 2.3 MeV gammas of Tl-208 would irradiate the weapon, its electronics, as well as providing an easily-detected alert to the world that U-233 was present in a location. In contrast, the alpha decay of U-235 and Pu-239 are rather easily shielded, making clandestine transport of these weapons much easier, as well as allowing long-term storage with relatively little damage to the electronics of the device. With all these drawbacks, it is not surprising that U-233 has not been utilized in operational nuclear weapons. …
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Jan 1, 2015
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