Thorium Instead Of Uranium: Solution To Our Energy Woes? Guest Post by James Mahaffey

Atomic Awakening: A New Look at the History and Future of Nuclear Power About a month ago, an article appeared in the Telegraph entitled, “Obama could kill fossil fuels overnight with a nuclear dash for thorium.” It’s central claim was that,

If Barack Obama were to marshal America’s vast scientific and strategic resources behind a new Manhattan Project, he might reasonably hope to reinvent the global energy landscape and sketch an end to our dependence on fossil fuels within three to five years.

This article (which should be read) was intriguing, but I am no expert on nuclear power generation, so I asked Randy Brich, who is. He in turn asked the expert’s expert, James Mahaffey, author of the highly regarded Atomic Awakening: A New Look at the History and Future of Nuclear Power.

Dr Mahaffey was kind enough to reply. Here is his take on thorium.


Ah yes. Thorium.

Thorium is 4 times more abundant in the Earth’s crust than uranium. It occurs in only one isotope, thorium-232. There is therefore no isotope separation, and 100% of the mined thorium is useful in a power reactor. Very little of the mined uranium is useful. You can’t make a bomb out of thorium.

BUT, thorium is not fissile. So, how do you burn it in a reactor? Thorium activates under neutron bombardment into uranium-233, which is quite fissile. All a thorium reactor needs is an aggressive neutron start-up source Once it gets going, it “breeds” U-233 in situ, and burns it. You can even run a converter operation in a thorium blanket, making U-233 for later use. No isotope separation is necessary for the uranium fuel. It’s pure, fissile U-233.

About 20% of the world’s thorium is in India. Putting two and two together, India has developed a thorium fuel cycle, and is currently working to build a thorium power economy. They’re building a full-scale power reactor right now. I think 30% of the thorium is in Australia. There’s plenty of it in the US. Brazil has a lot of thorium (the black sand on the beaches is thorium oxide) and they have phased in and out of a try for energy independence over the past 40 years.

So, why have we not built any thorium reactors in this country? Actually, we have. The Shippingport Power Station, the first commercial nuke plant in the US, used a thorium blanket and became a thermal breeder reactor with its second fuel loading. Fort St. Vrain was a thorium reactor. The molten salt reactor experiments, including the one at Oak Ridge, were thorium reactors. But, it has never caught on because the nuke industry is so utterly committed to uranium fuel. Everything, from core designs to fuel fabrication, depends on the fuel being uranium.

An advantage of the molten salt thorium reactor: there’s no fuel fabrication. The fuel is dissolved in the coolant. Refueling is maybe once every 10 years. The entire primary loop is full of fuel. It only goes critical in the reactor vessel, where the shape and volume make it critical. The molten salt runs at atmospheric pressure. No explosions in the primary.

How did this happen? The first criticality experiments were with U-235 as the fissile component. Everything had to fall into place behind U-235, under the frantic war-time conditions, and there was no diversion into other, more promising avenues. Imagine, if the B-reactor1 had been configured a little differently, it could have made U-233 instead of Pu-239. There would have been no need for the tricky implosion setup. U-233 has no spontaneous fission problem. No need for tedious isotope separation. They could have turned out cheap “gun-assembly” bombs by the hundreds.

The Alsos mission turned in a big scare in 1944. They found that the retreating Germans has taken with them a big load of thorium out of Paris. Were the Germans short-cutting to a U-233 assembly weapon? No, they weren’t. The Germans were anticipating a post-war craze for radioactive cosmetics.

Why didn’t we at least divert into thorium development for weapons after the war? Excellent question. In the 50’s, the Army wanted its own nuclear arsenal, separate and specialized. The MK 33 240mm artillery shell was developed. The Air Force hit the ceiling. The small, 8-inch shell would have to be a gun-assembly weapon, and that meant it would use the preciously small supply of bomb-grade high-enriched uranium (HEU). The Air Force got there first with its weapons needs, and they were not willing to share. Fine, said the Army, we’ll use U-233. They started work on the chemical processing and handling facilities for U-233, which had never been built before.

Los Alamos National Lab stepped in and nixed the concept of using U-233. I’m not exactly sure why. They cited “handling problems.” The MK 33 became the W-33/M-422, using fully enriched uranium.

You will hear that we can’t make bombs out of U-233 because it is a virulent gamma-ray emitter. This is not true, and I find it curious that it is used as a reason. U-233 has a 158,000-year half-life. What they are referring to is the protactinium-233 contaminant, which has a 27-day half-life, beta-decaying into U-233 with gamma-ray involvement. Chemically scrub the protactinium, of course, or just wait a year and it will be gone.

The US has a moderately large stockpile of U-233 in Oak Ridge. They are presently arguing that it should be buried along with the rest of the fission waste. Why? Why ruin a potential energy resource? Fear of theft? We sit on a lot of HEU, so why the worry over U-233? It’s a bit odd. There’s a lot they aren’t saying.

Don’t get me started about thorium!

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1 Update: The B-reactor was the first of several plutonium production reactors built at the Hanford Works in Richland, WA, in 1943. It was the first reactor built to run at high power. Graphite, natural uranium, and water cooled. It used excess neutrons to convert U-238 into Pu-239. The same load of excess neutrons could have been used to convert Th-232 into U-233.

14 Comments

  1. Given the principle that “if it is too good to be true …”, what are the drawbacks to Thorium beyond overcoming legacy cost issues?

  2. The high energy, deadly gamma rays that made handling U-233 difficult actually come from an inevitable coproduct of neutron irradiation, U-232. This discourages weapons proliferation using U-233. There is an upcoming conference at the Royal Institution. Visit itheo.org for more.

  3. If someone wanted to invest in a company likely to benefit from a move to Thorium, what would the likely candidates be? Not just ltd to the US. Is there an Indian corp involved there?

  4. “What are the drawbacks to Thorium … ?”
    The net advantages of thorium in a solid fuel reactor are modest except in the mission to destroy plutonium. The real gain is using thorium in a liquid fuel reactor. Use in such a reactor provides dramatic benefits. But liquid fuel reactor is also the drawback – namely to do anything involved with nuclear in the US one must get the NRC to approve what you are doing. The NRC must in turn be confident that what is proposed is VERY safe for the public. Their focus is on solid fuel reactors, they have experts in that field, they have established design principals and are on solid ground when they declare something safe. Reviewing a liquid fuel reactor would require the development of new experts, new methodologies, and new standards. No breakthrough science is needed but it will take lots of good engineering. The NRC feels it does not have the budget or mandate to consider a liquid fuel reactor and waits on Congress to provide both the funding and mandate.
    Private company investment will be very limited until they can see a path forward to get such a reactor approved.

  5. Thorium was tried in the US as the fuel for the first reactor at Indian Point New York. The reactor operator, Consolidated Edison, switched to uranium fuel after the first cycle. Thorium isn’t as rosy as its advocates would have us believe. If it was such a good fuel, why is India searching so hard to find uranium.?

    U233 is considered to be as good as U235 for weapons. Lots of research has been conducted, but thorium has not been able to displace uranium as a commercial reactor fuel.

  6. Recently the IAEA “Red Book” report has been being updated every odd-numbered year. One cannot, within reason, buy it, but the upshot is published free:

    … total identified resources amounted to 6 306 300 tU, an increase of about 15% compared to 2007, including those reported in the high-cost category (less than USD 260/kgU or less than USD 100/lbU3O8) …

    That increase works out as 1144 tonnes per day, and that means if there were enough power reactors in the world, of the types that are common today, that their heat production equalled the heat production of all petroleum burners, they could not keep up.

    They could not keep up with the increase in reserves. And note, this has been happening with a uranium price one-eightieth that of petroleum, and a worldwide uranium exploration budget, I guess, about equal to what is spent on toy flying discs — “Frisbees” and similar devices.

    So the abundant power that thorium can provide for a very, very, very, very long time is redundant, because of the extreme abundance of 235-U, for a time that is merely very, very long.

    (How fire can be domesticated)

  7. My father designed nuclear reactors in the 70’s, and he told me the reason for steam + uranium is the inherent fail-safes in the system. Between the water and the dampening, you’ve got a much safer system than a molten-salt moderated reaction.

  8. Steam + uranium reactors, as they are designed for commercial use, are the most dangerous. Due to concerns about diversion to weapon use, the fuel is not as highly refined as in military reactor applications like subs. The problem is that after use, radioactive transuranic elements build up in the spent fuel. Even when you push the control rods into the reactor to stop the reaction, the transuranics continue to release heat and require that the cooling system continue to function for a long time to keep them from melting down the fuel assembly. You thus need not only a connection to the grid to keep the pumps running, but emergency generators in case the grid goes down when a reactor is taken offline. This is not as great a problem in the higher enrichment military applications.

    Also, given that the system is pressurized, any break in the cooling loop can cause the heated water in the core to turn into steam which doesn’t have the heat capacity of water leading to a meltdown. That’s what cooked Three Mile Island (a stuck control valve was the cause of the leak, not a pressure break). The only reason high pressure is used is for thermodynamic efficiency. Plain boiling water reactors aren’t nearly as efficient.

  9. When the excitement at Chernobyl occurred, Her Majesty’s Government immediately sought expert help. The experts included my boss, who roped me into it to. The main lesson I learnt was that HMG was able to lay hands on a huge pile of info on Chernobyl in next to no time. For government work, it really was bloody impressive.

  10. Another cold war oddity was the Davy Crockett system, the M-28 and M-29 firing the W54. A ‘nuclear bazooka’ I’m not sure I’d want to be anywhere either end of. Part of the problem with convincing people nuclear power is safe is breaking the link in people’s minds between weapons and steam generators. Given the money anti-nuclear groups have invested in negative PR, that’s a challenge to overcome the fear.

  11. Dr Mahaffey seems to have missed the point.

    What was apparently a response to the issue of thorium nuclear power to replace fossil fuels ends up being a rant on wasted weapons potential???

    Must everything be returned to the lowest common denominator of WAR?

    What about the application of thorium in replacing fossil fuels? Is there less waste? Is it safer?

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