Thorium and uranium represent the heaviest naturally occurring elements on Earth. Both were named after ancient gods: Uranus was the principal Greek god of the sky while Thor was the Norse (and broadly Germanic) god of a thunder.
There's a modern mythology surrounding thorium and uranium too, such as the currently very popular suggestion that thorium can replace uranium and deliver much better (safer, cheaper, fuel abundant) nuclear energy.
Well, we've heard all these things from advocates of nuclear energy before, haven’t we? Weren’t we told in the 50’s, 60’s, 70’s, 80’s, 90’s and even until recently that all these miracles would actually be delivered by uranium fueled reactors? Yeah, something obviously went wrong because none of those dreams actually came true, despite half a century's worth of effort and hundreds of billions in subsidies poured into the nuclear industry.
What are the chances that replacing the Greek god with a Germanic one will help? Would Thor take his powerful hammer and nail it all down? Not likely.
Thorium technology is in principal based on nuclear fission and therefore keeps fission's inherent problems. While it partially addresses some of the downsides of current commercial reactors based on uranium (plutonium) fuel, such as limited reserves of uranium and unwanted production of plutonium and transuranic isotopes, it still has significant issues related to fuel mining and fabrication, reactor safety, production of dangerous waste, and the hazards of the proliferation of nuclear weapons.
Let’s look more closely at some of the hopeful claims around thorium.
Safer reactors? The risks inherent in nuclear reactors are due to the massive concentrations of radioactive materials and the huge amount of heat they produce (which is actually needed to generate electricity). No matter if the fuel is based on uranium or thorium, if it’s solid or liquid, this characteristic alone will inevitably continue to be the Achilles heel of any nuclear reactor. As you can read in the Union of Concerned Scientists’ briefing on this issue, the truth is that the U.S. Department of Energy concluded in 2009 after a review that “the choice between uranium-based fuel and thorium-based fuel is seen basically as one of preference, with no fundamental difference in addressing the nuclear power issues [of waste management, proliferation risk, safety, security, economics, and sustainability].”
Less nuclear waste? It’s obvious that fission applied to different nuclear fuel results in a different composition of radioactive waste. But it's still radioactive waste and whether the waste produced by thorium reactors is less problematic (because there's no plutonium in it) remains a question. Spent thorium fuel still contains long-lived isotopes such as proactinium-231 (with a half-life 32,000 years which is even longer than plutonium Pu-239) which implies the need for long term management in timescales comparable to typical high level waste from uranium reactors. Not surprisingly, a chart published in Nuclear Engineering International magazine in November 2009 shows that the radiotoxicity of spent thorium fuel is actually higher than uranium spent fuel over the long term, ie after first 10,000 years:
No proliferation? Yes, thorium can’t itself be used to build nuclear weapons but it can’t be used directly as a nuclear fuel either. In fact, it has to be first converted into the fissile uranium isotope, U-233. That's an isotope that is suitable for nuclear weapons. The US successfully detonated a nuclear bomb containing U-233 in 1955.
Even the UK Department of Energy and Climate Change commissioned a report which concluded in 2012 that the claims by thorium proponents who say that the radioactive chemical element makes it impossible to build a bomb from nuclear waste, leaves less hazardous waste than uranium reactors, and that it runs more efficiently, are "overstated".
Thorium reactors exist only in blueprints and early experiments, which means there could be other issues not yet detected that would complicate their large scale implementation. In any case, this also means that it would take much longer than a decade before thorium reactors would potentially become available for a larger commercial deployment.
Recent studies, like the one published by the Norwegian thorium commission, while being supportive of the concept, also conclude that there are many uncertainties and problems related to it. It notes that Norwegian thorium reserves are of limited economic attractiveness compared to other sources; that accelerator-based reactors will be viable in the distant future at best; that thorium reactors would create nuclear waste problems; and that any of this will require massive international research.
Related to this is thorium's unknown economic performance. Experts suggest that one of the key reasons why thorium reactors are not being developed is that they cannot compete economically with uranium fuel-based reactors, due to more complicated fuel fabrication and processing. And current pressurized water reactors are already uncompetitive. With investment costs of current reactor technology easily reaching 8,000 USD/kW of installed capacity, it is difficult to imagine that thorium reactors would be developed and built in foreseeable future.
All in all, it rather looks like the nuclear industry, failing terribly to provide a reliable and affordable energy source, is trying to divert our attention from its scandals and incompetence to a distant, rosy dream. Not bad PR but not much else.
While we are once again told to dream about a bright nuclear future, modern renewable energy technologies are already cheaper and upscaled well beyond nuclear: in 2013, while only 4,000 MW was globally installed in four single reactors, installations of wind and solar combined reached 80,000 MW. Those newly added capacities of wind and solar alone will generate, on an annual basis, as much electricity as twenty large reactors.
Let’s not get distracted. Let’s not waste even more time, money and brainpower on trying to make the impossible: a nuclear energy source that would actually really work. The future is renewable, and that’s where we need to go as quickly as possible.
Jan Beránek is the leader of Greenpeace International’s Energy Campaign