As climate change makes the planet less pleasant to live on, nuclear power is getting more attention. Solar and wind energy can help cut greenhouse gas emissions, but if a solution can be found to climate change, nuclear power is probably going to be part of it.
But although nuclear power is carbon-free, it's risky. For starters, disposing of radioactive waste from nuclear power plants presents an insoluble problem — what to do with such dangerous byproducts? Also, what happens if the core melts down and creates a deadly environmental catastrophe, as happened in Fukushima, Japan, in 2011? There are other concerns as well, but there are a lot of reasons to keep plugging away at making nuclear power safer.
Nuclear reactors are run by fission, a nuclear chain reaction in which atoms split to produce energy (or in the case of nuclear bombs, a massive explosion).
"Approximately 450 nuclear reactors are in operation worldwide, and they all need fuel," says Steve Krahn, a professor in the department of civil & environmental engineering at Vanderbilt University, in an email. "For the most part, these reactors operate on Uranium-235 (U-235), and the nations that partially recycle the fuel — France, Russia and a few other countries — mix in a little recycled Plutonium-239 to make what's called mixed-oxide fuel."
Plutonium is a byproduct of used fuel from a nuclear reactor; it's highly toxic and its radioactivity doesn't drop very quickly — it takes tens of thousands of years for it to achieve safe levels of radiation, whereas thorium breaks down to a safe level in around 500 years.
What Is Thorium?
Some scientists think the element thorium is the answer to our nuclear problems. Thorium is a slightly radioactive, relatively abundant metal — about as abundant as tin and more abundant than uranium. It's also widespread, with particular concentrations in India, Turkey, Brazil, the United States and Egypt.
Thorium isn't a fuel like uranium. The difference is that uranium is fissile, meaning that it produces a runaway chain reaction if you can get enough uranium in one spot at one time. Thorium, on the other hand, is nonfissile or "fertile," meaning you have to bombard the thorium with neutrons — essentially jump-start it with a small amount of radioactive material like uranium — so it can transmute into a uranium isotope (U-233/Th-232) for creating power.
Thorium Pros and Cons
Thorium was used in a lot of early nuclear physics experiments — Marie Curie and Ernest Rutherford worked with it. Uranium became more heavily associated with the nuclear process during World War II, because uranium is better for making bombs, but for power generation, thorium has some real benefits over uranium. Thorium is more efficient than uranium, and its reactors may be less likely to melt down because they operate at lower pressures. In addition, less plutonium is produced during reactor operation, and some scientists argue thorium reactors could destroy the tons of dangerous plutonium waste that have been created and stockpiled since the 1950s. Not only that, thorium is thought to be nearly proliferation-proof, since plutonium can't be separated out of the waste products and used to make bombs.
There are a few downsides to thorium, however. One is that, although thorium and its waste products are dangerous for hundreds rather than tens of thousands of years compared with uranium or plutonium, thorium is actually more dangerously radioactive in the short term. For that reason, thorium can be a bit harder to work with, and it's trickier to contain it. It is also more difficult to prepare than uranium rods: According to Krahn, if we are going to power our planet using a thorium fuel cycle, sufficient U-233 must be produced to fuel the initial reactors.
"Methods to chemically process Th-232 and U-233 are fairly well established; however, facilities to accomplish such chemical processing would need to be constructed," says Krahn.
Using Thorium for Energy
There are several ways thorium could be applied to energy production. One way is to use solid thorium fuel in a conventional water-cooled reactor, similar to modern uranium-based power plants. Another prospect that has been exciting to scientists and nuclear power advocates is the molten salt reactor. In these plants, fuel is dissolved in a vat of liquid salt. The salts have a high boiling point, so even huge temperature spikes will not lead to explosions. In addition, molten salt reactors don't require a lot of cooling so they don't need a huge amount of water to operate. For that reason, a thorium-powered nuclear reactor is being tested in the Gobi Desert in China.