Thorium reactors have long been proposed as a cleaner, safer alternative to conventional nuclear energy, and now a new Russian study has added another potential benefit to the mix. Scientists from Tomsk Polytechnic University (TPU) propose a new thorium reactor design that can burn weapons-grade plutonium, producing power and thermal energy while disposing of nuclear waste at the same time.
Weapons-grade plutonium (plutonium-239) is one of the dangerous radioactive by-products of nuclear power, and with a half-life of over 24,000 years, it's tricky to store and dispose of. The substance is still packed with potential energy, but reusing it requires chemical processing that can be expensive and complicated.
Enter thorium. This element is more abundant in nature, cleaner and potentially more efficient than uranium, so thorium reactors have long been proposed as a viable alternative to conventional nuclear reactors. Unfortunately, the properties that make it attractive also raise new obstacles.
Once things get cooking in a nuclear reactor, the chain reaction can essentially keep feeding back into itself. Neutrons strike the nucleus of the atoms of the fuel source (usually uranium), breaking it into its components and releasing energy in a process known as fission. More neutrons are released along with the energy, which can in turn be used to fission other atoms.
The problem is, that self-sustaining cycle can also lead to nuclear power's most devastating downside. If operators lose control of that chain reaction or fail to properly keep it cool, a meltdown can occur, resulting in disasters like those seen at Chernobyl and Fukushima.
By itself, thorium can't sustain that feedback loop. That means it won't get out of hand on its own, but to produce power it still requires some other radioactive material. And that's where the TPU study comes in.
The Russian researchers plan to use weapons-grade plutonium to fuel that reaction, giving the reactor the safety benefits of thorium while also disposing of the nuclear waste. According to the team the reactor can burn almost all of the plutonium, and the waste material that's produced is a mix of graphite, plutonium and other decay products that no longer pose a nuclear hazard.
"Large amounts of weapons-grade plutonium were accumulated in the Soviet era," says Sergey Bedenko, an author of the study. "The cost for storing this fuel is enormous, and it needs to be disposed of. In the US, it is chemically processed and burned, and in Russia, it is burned in the reactors. However, some amount of plutonium still remains, and it needs to be disposed of in radioactive waste landfills. Our technology improves this drawback since it allows burning 97 percent of weapons-grade plutonium. When all weapons-grade plutonium is disposed of, it will be possible to use uranium-235 or uranium-233 in thorium reactors."
The proposed thorium reactor has other advantages as well. The plant requires relatively low input energy, from 60 MWt, which can make them up to 50 percent more efficient than other reactors. Waste heat can also be harnessed for desalination of water or to produce hydrogen fuel, according to the researchers.
"The main advantage of such plants will be their multi-functionality," says Bedenko. "Firstly, we efficiently dispose one of the most dangerous radioactive fuels in thorium reactors, secondly, we generate power and heat, thirdly, with its help, it will be possible to develop industrial hydrogen production."
Thorium reactors have been discussed almost as long as nuclear energy has, but the technology has never been successfully developed. Renewed focus on environmentally friendly energy in recent times has seen scientists begin to experiment with thorium-based nuclear power again after 40 years, and this latest development could lend further impetus to getting it off the ground.
The research was published in the journal Annals of Nuclear Energy.
Source: Tomsk Polytechnic University
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