August 13, 2022 15:02

Thorium reactors — a viable alternative?

Image: Wikipedia.
Image: Wikipedia.


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Molten salt breeder reactors look good on paper, but just how applicable are they to solving the problem of low-emission maritime propulsion?

After the War, nuclear reactors were hailed as the energy source of the future and uranium became the world’s favoured nuclear fuel, but it was not the only option for nuclear power. Thorium also showed promise as a fuel source, offering cleaner, safer power with less potential for nuclear proliferation.

An experimental thorium molten-salt reactor first ran at the Oak Ridge National Laboratory for around 15,000 hours from 1965 to 1969, and in 1968, Glenn Seaborg announced to the US Atomic Energy Commission (AEC) that a thorium-based reactor had been developed and tested.

But, despite the benefits — greater safety, a greater abundance of fuel, superior physical and nuclear properties, and reduced nuclear waste — thorium reactors were side-lined and over time the technology faded from view. In 1972, the US government discontinuing research and development into thorium reactors altogether.

There is a vital difference between uranium and thorium; the ability to be weaponised. The US government was interested in profitability and weapons first, and safety second, so it chose uranium. Yet many in the scientific community favoured thorium as a power source and the director of Oakridge, Alvin Weinberg, championed its greater safety.

Recalling the period, Weinberg said: ‘[Congressman] Chet Holifield was clearly exasperated with me, and he finally blurted out, “Alvin, if you are concerned about the safety of reactors, then I think it may be time for you to leave nuclear energy.” I was speechless. But it was apparent to me that my style, my attitude, and my perception of the future were no longer in tune with the powers within the AEC’.

Weinberg saw the potential for a new kind of reactor, one with a zero risk of meltdown, but he was forced out of the AEC and his work shelved. The arms industry had won, uranium became the nuclear fuel of choice, and the world was denied a source of safe, sustainable, low-emission power. As a result, many in the scientific community have been unaware of the technology’s potential and new research has been slow in coming.

The World Nuclear Association says there are seven types of thorium reactor, but molten salt reactors using a liquid fluoride salt/thorium fuel-mix show the greatest promise for marine use.

Liquid fluoride thorium reactors (LFTR) are fundamentally different from uranium reactors. Their liquid salt coolant allows higher operating temperatures and if they malfunction, the salt simply solidifies and all fissile material is contained.

So, on paper, at least, they would seem to be the perfect energy source for marine propulsion, offering sustainable, low-emission power and a fuel source that is three times as abundant as uranium. However, there are major hurdles to the technology becoming commonplace.

Research needs funding, and that won’t happen until it can be demonstrated that thorium reactors offer a cheap alternative to fossil fuels. Investors and manufacturers want to know they will make a profit, so it’s going to take someone with capital and nerve to prove to the world that the technology works and is a viable marine power source.

But an even bigger problem is the lack of a joined-up global response to climate change and the necessary international agreements that would allow nuclear-powered ships to ply the high seas and territorial waters, and to dock anywhere in the world.

When those essential requirements are met, then, and only then, might we be on the lookout for thorium-powered ships at sea and in our harbours.


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One Response

  1. Interesting article and I showed it to one of my friends an expert in the field – he responded as follows:
    If you want, you can take direct contact with him.
    Hei Dagfinn,
    Thanks for sending this over.
    It’s nice that articles are written about this topic, but the author makes two essential mistakes which skews the narrative in the wrong direction.
    They’re easily corrected however.
    The first is the confusion between the MSR and Thorium. The MSR is an engine, and Thorium is a fuel. In the same way you could burn all manner of fuels in a combustion engine, you wouldn’t fundamentally differentiate between a diesel engine, a gasoline engine, an ethanol engine or even the ones they used to have in our old M6 army trucks that were rumoured could run of whiskey and butter.
    Molten Salt Reactors are by nature fuel agnostic. You can use Uranium, Plutonium, Thorium, or theoretically any kind of -ium.
    Alvin Weinberg and Eugene Wigner (both real heroes imho) never built a Thorium MSR. They didn’t get that far. They built an MSR (called the MSRe) in the 1960s which ran on 3 fuel cycles: U235/U238, PU239/U238 and U233/U238. It’s one of 3 MSRs to have been built and it functioned really well, even then.
    The U233/238 fuel cycle is significant because U233 is the fuel in a thorium reactor not the Thorium itself. Thorium is not a fuel, it is a feedstock for a fuel, and that fuel is U233. U233 is a ferociously radioactive daughter isotope of Thorium which does not occur in nature, but has to be made from Thorium. It doesn’t matter how much thorium you have (like in Telemark), unless you can make U233, it’s not useful for anything. Making U233 is not a trivial matter.
    Therefore, there really is no such thing as a Thorium reactor. It’s a U233 reactor like the (Liquid Fluoride Thorium Reactor) LFTR referenced in the article. The LFTR is based on the MSRe but taken one theoretical step further, where instead of running one fuel, you’re running two. One fuel (the U233) is the fissile which produces heat that powers a turbine to make electric power, and one is the ‘blanket’ feedstock (the Thorium) which picks up neutrons from the fierce radioactivity of the U233, and then transmutes into more U233 (its daughter isotope).
    It’s a nice theory, but it requires the reactor core to run on 100% pure U233.
    The second error is the weapons angle. U233 is one of the most violently radioactive elements that exists, and is an excellent nuclear weapons material. A 100% pure U233 core is a problem for proliferation just like a pure plutonium core would be, certainly for shipping. What makes it hard to use for bombs, is its intense radioactivity which makes it very hard to handle. The argument that the US chose uranium instead of thorium because of the weapons program is a conspiracy theory which proliferates on the internet. It sounds logical, but so do most conspiracy theories. In fact the US developed a U233 nuclear device that detonated quite successfully back in the 40s.
    The correct narrative of the article should be focused on the MSR, not the fuel and the headline really should be ‘MSRs – a viable alternative?’
    The MSR we are building in the US has all the characteristics described. It runs low enrichjed material so cannot be weaponised. It can’t meltdown, can’t expel toxins into the environment and will run for decades on the same fuel load without refuelling. If we wanted to feed it with Thorium, we could but it would have to be demonstrated what specific economic advantage that would bring. I haven’t seen one yet, and believe me, I have looked high and low.
    Hope this is helpful.

    With best wishes,
    Mikal Bøe
    Chief Executive Officer

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