Thorium was discovered nearly 200 hundreds years ago by the Swedish scientist Jakob Berzelius (1779-1848), who named the new element after Thor, the mythical nordic God of Thunder . Though widespread in nature and more abundant than, for example uranium, thorium does not occur in any deposits at a high concentration. Rather, it is a frequent low-level "contaminant" in some minerals such as monazite, a cerium phosphate.
Since its discovery, thorium has pretty much remained a non-entity in technology and commerce. Except for a few specialty applications, there really was no great use for it – until now. The anticipated change in its importance is due to its existence in many different isotopes (only a few of which are naturally occurring) and ability to deliver power via a nuclear fission process, similar to uranium, in other words, as a different kind of nuclear reactor fuel for electricity generation.
Advantages, Limitations, and Disadvantages of Uranium
Uranium-based reactors are basically straightforward. They require uranium-235 (235U) isotope enriched material (at 3 to 20%, depending on the type of reactor) to work. In natural ores, the 235U isotope is present at only 0.7%. In order to obtain fissionable material, the low-grade uranium needs to be enriched, using thousands of high-speed centrifuges exploiting a minute molecular weight differential of the hexafluorides between the different uranium isotopes. However, this enrichment process requires substantial energy.
Uranium-based nuclear reactors create substantial amounts of "depleted," but still quite radioactive material. This needs to be stored in a safe facility – for millions of years – to allow the natural decay process to "dispose" of its radioactivity. The problem of long-term and safe disposal of such wastes has been around for decades, both in North America and in Europe, but no acceptable resting place has yet been found.
More recently, another limitation of the uranium reactor is becoming apparent. Though new deposits are being found and mined regularly, the supply of easily mineable uranium is probably not keeping up with the foreseeable demand over the next decades. In fact, these days, much of the fissionable uranium does not come from mining but from nuclear warheads built by the superpowers since WWII. This supply is expected to become exhausted in a few years.
Advantages of Thorium for Nuclear Power
Early thorium-based nuclear reactors were unsuccessful, mainly due to technical problems. Therefore, uranium-based systems were developed instead. They provide now anywhere between 25 and 50% of the North American electricity needs, depending on the state or province. Now, a revival may be on the way for thorium. The reasons are as follows.
With modern mining and ore-processing methods, the supply of thorium can easily be ramped up to sustain a much larger level of production. Substantial supplies are available on several continents, including North America. According to the Thorium Energy Alliance , an educational advocacy organization, "there is enough thorium in the United States alone to power the country at its current energy level for over 1,000 years."
The real advantage of thorium reactors comes from the nuclear process involved. In contrast to uranium, the thorium process consumes 100% of the fissionable element versus less than 1% of the uranium process. That also means that it produces substantially less of long-lived radioactive waste material than the uranium reactor. One disadvantage with a thorium reactor is that it needs constant priming with 235U or a similar neutron source in order to sustain its nuclear process. However, this disadvantage also brings another advantage with it: A thorium reactor could not suffer a core "meltdown," such as happened in Chernobyl. Therefore, while thorium creates additional technological hurdles, it also would be much safer all around.
The technological problems experienced with earlier attempts to build thorium-type reactors pertained mostly to separating low levels of thorium oxide from other materials. However, modern chemistry appears to have solved that issue.
Another advantage of a thorium reactor is that it is difficult to create any nuclear bomb material with it. Of course, some might view that as a drawback.
As of late, several countries including China, India, Japan, Russia and the United States have plans to use thorium for new nuclear reactors. In fact, India has been building an advanced design which was claimed to be ready for operation in 2011. No recent news is available, but more information and technological advances can be expected in time.
In the US, Britain, Canada, Germany, no new nuclear reactors have been built for several decades. Several existing plants are getting close to their design life-spans; some are already beyond their "best before date."
Nuclear reactors currently provide a large fraction of the electricity used in North America. Many of these reactors need to be replaced in the foreseeable future. I think this is a perfect time to invest in research and development of the promising thorium-based technology for their replacement.