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.
Although nuclear power doesn’t produce the climate-altering gases that create a problem with other sources of electricity, it carries with it certain risks. For starters, disposing of radioactive waste from nuclear power plants presents a difficult problem — what to do with such dangerous byproducts? Also, what happens if the core melts down and creates an environmental catastrophe, as happened in Chernobyl, Ukraine, in 1986? There are other concerns as well, but given our current energy predicament, there are plenty 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. He noted that 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 recycled Plutonium-239 to make what's called mixed-oxide fuel.
Plutonium is a byproduct of used fuel from a nuclear reactor and it can form the basis for recycling nuclear fuel from today’s nuclear reactors, as is done in France and several other countries. However it's highly toxic and it is the most frequently used material for nuclear weapons, which is one reason scientists have continued to explore other options.
What Is Thorium?
Some scientists think the element thorium is the answer to our nuclear power 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.
But it is important to note that thorium isn't a fuel like uranium. The difference is that uranium is “fissile,” meaning that it produces a sustainable chain reaction if you can get enough uranium in one spot at one time. Thorium, on the other hand, is not fissile — it’s what scientists call "fertile," meaning that if you bombard the thorium with neutrons (essentially jump-start it in a reactor fueled with material like uranium) it can transmute into a uranium isotope uranium-233 which is fissile and suitable for creating power.
Thorium Pros and Cons
Thorium was used in some of the earliest nuclear physics experiments — Marie Curie and Ernest Rutherford worked with it. Uranium and plutonium became more heavily associated with nuclear processes during World War II, because they provided the clearest path to making bombs.
For power generation, thorium has some real benefits. Uranium-233 formed from thorium is more a more efficient fuel than uranium-235 or plutonium, and its reactors may be less likely to melt down because they can operate up to higher temperatures. In addition, less plutonium is produced during reactor operation, and some scientists argue thorium reactors could destroy the tons of dangerous plutonium that has been created and stockpiled since the 1950s. Not only that, a fleet of reactors operating on thorium and uranium-233 is thought by some scientists to be more proliferation-resistant, since more sophisticated technology is needed to separate uranium-233 out of the waste products and use it to make bombs.
There are downsides to thorium, however. One is that, thorium and uranium-233 are more dangerously radioactive to chemically process. For that reason, they are harder to work with. It is also more difficult to manufacture uranium-233 fuel rods. Also, as noted earlier, thorium is not a fuel.
“If we are going to power our planet using a fuel cycle that employs thorium and uranium-233, sufficient uranium-233 must be produced in other types of reactors to fuel the initial uranium-233 reactors,” says Krahn. “If that can be accomplished, methods to chemically process thorium-232 and uranium-233 and manufacture fuel from them are fairly well established; however, facilities to accomplish these processes would need to be constructed.”
Using Thorium for Energy
There are several ways thorium could be applied to energy production. One way under investigation now is to use solid thorium/uranium-232 fuel in a conventional water-cooled reactor, similar to modern uranium-based power plants. In fact, more than 20 reactors world-wide have been operated with fuel made of thorium and uranium-233. Another prospect that has been exciting to scientists and nuclear power advocates is the molten salt reactor. In these plants, fuel is dissolved in liquid salt that also acts as the coolant for the reactor. The salt has a high boiling point, so they can be more efficient in electricity generation and even huge temperature spikes will not lead to massive reactor accidents such as occurred at Fukushima. It might sound like this kind of reactor is almost the stuff of science fiction, but just such a reactor was operated in the United States in the 1960s and is currently being built in the Gobi Desert in China.