Do thorium reactors prevent nuclear weapons proliferation risks?

[Ellen Thomas]

-------- Forwarded Message --------

Subject:	Do thorium reactors prevent nuclear weapons proliferatiion risks?
Date:	Mon, 1 Jul 2024 02:10:27 -0400
From:	Gordon Edwards <cc...@web.ca>

Do thorium reactors prevent nuclear weapons proliferatiion risks?

Many people have been assured, incorrectly, that the use of thorium as a “nuclear fuel” eliminates the danger of nuclear weapons proliferation. That is simply untrue.

The fact is, thorium is NOT a nuclear fuel. However, a thorium-232 atom can be transmuted into a uranium-233 atom by capturing a stray neutron, and uranium-233 (not generally found in nature) is an excellent nuclear fuel and can also be used to make excellent nuclear weapons. So a “thorium reactor” is really a uranium-233 reactor.

Natural thorium — thorium-232 -- is not fissile (i.e. it is not a chain-reacting material). So thorium requires a concentrated fissile material to be added to it, in order to get a chain reaction going and produce the neutrons that are needed to transmute thorium-232 atoms into chain-reacting uranium-233 atoms. 

That concentrated fissile material additive does not have to be enriched uranium, it can equally well be plutonium. It has to be either one or the other, there is no other choice. So, in any event, to get a “thorium reactor” going, you need to use either uranium (enriched to a rather high degree) or plutonium (extracted from used nuclear fuel) as an additive. In either case, you will need to use proliferation-sensitive technologies (uranium enrichment or plutonium extraction) before even embarking upon a thorium reactor program. 

Thorium use is therefore not a proliferation-resistant plan of action, not even to begin with.

It gets worse, because subsequently, if the “thorium-impregnated-with-fissile material” is irradiated in a reactor, the thorium atoms will FIRST be transmuted into protactinium atoms (protactinium-233) which will then spontaneously “decay” into uranium-233 atoms. In addition, further neutron captures inside the reactor will also produce a small amount of uranium-232, an undesired pollutant that is a strong gamma emitter.

Thorium enthusiasts often say that the powerful gamma rays from U-232 will make the U-233 unusable for nuclear weapons, which is somewhat of an exaggeration to begin with.

However, if the protactinium-233 is chemically separated out from the irradiated “thorium fuel" outside the reactor, those protactinium-233 atoms will spontaneously decay into pure uranium-233 atoms without any admixture of uranium-232 (because there are no neutrons outside the reactor to create uranium-232 as a result of additional neutron captures),

Since pure U-233 can be produced spontaneously outside the reactor, as outlined above by separating out protactinium-233 first, this procedure can completely avoid the problem of U-232 contaminating the U-233 — which, admittedly, would make nuclear weapons construction more difficult (although not impossible). 

So the complicating factor of U-232 can be circumvented entirely by a would-be proliferator. There is no doubt that U-233 is an extremely powerful nuclear explosive material and, uncontaminated, can be used to make arsenals of nuclear weapons with relative ease. 

Thus thorium reactors do not “eliminate” or even significantly reduce the problem of nuclear weapons proliferation.

Cheers,

Gordon Edwards.

P.S. Here’s a Bulletin of Atomic Scientists argument followed by an analysis of thorium as reactor fuel and as a nuclear explosive written by myself some years ago.

https://thebulletin.org/2014/05/thorium-the-wonder-fuel-that-wasnt/#post-heading

 

https://thebulletin.org/2014/05/thorium-the-wonder-fuel-that-wasnt

 

From: Gordon Edwards

 

 The Hype About Thorium

 

There has recently been an upsurge of uninformed babble about thorium as if it were a new discovery with astounding potentiality. Some describe it as a nearly miraculous material that can provide unlimited amounts of problem-free energy. Such hype is grossly out of context.

 

Thorium and Nuclear Weapons

 

One of the most irresponsible statements is that thorium has no connection with nuclear weapons. On the contrary, the initial motivation for using thorium in nuclear reactors was precisely for the purposes of nuclear weaponry.

 

It was known from the earliest days of nuclear fission that naturally-occurring thorium can be converted into a powerful nuclear explosive – not found in nature – called uranium-233, in much the same way that naturally-occurring uranium can be converted into plutonium.

 

Working at a secret laboratory in Montreal during World War II, nuclear scientists from France and Britain collaborated with Canadians and others to study the best way to obtain human-made nuclear explosives for bombs. That objective can be met by converting natural uranium into human-made plutonium-239, or by converting natural thorium into human-made uranium-233. These conversions can only be made inside a nuclear reactor. 

 

The Montreal team designed the famous and very powerful NRX research reactor for that military purpose as well as other non-military objectives. The war-time decision to allow the building of the NRX reactor was made in Washington DC by a six-person committee (3 Americans, 2 Brits and 1 Canadian) in the spring of 1944.

 

The NRX reactor began operation in 1947 at Chalk River, Ontario, on the Ottawa River, 200 kilometres northwest of the nation’s capital. The American military insisted that thorium rods as well as uranium rods be inserted into the reactor core. Two chemical “reprocessing” plants were built and operated at Chalk River, one to extract plutonium-239 from irradiated uranium rods, and a second to extract uranium-233 from irradiated thorium rods. This dangerous operation required dissolving intensely radioactive rods in boiling nitric acid and chemically separating out the small quantity of nuclear explosive material contained in those rods. Both plants were shut down in the 1950s after three men were killed in an explosion.

 

The USA detonated a nuclear weapon made from a mix of uranium-233 and plutonium-239 in 1955. In that same year the Soviet Union detonated its first H-bomb (a thermonuclear weapon, using nuclear fusion as well as nuclear fission) with a fissile core of natural uranium-235 and human-made uranium-233.

 

In 1998, India tested a nuclear weapon using uranium-233 as part of its series of nuclear test explosions in that year. A few years earlier, In 1994, the US government declassified a 1966 memo that states that uranium-233 has been demonstrated to be highly satisfactory as a weapons material. 

 

Thorium and Uranium in Nuclear Reactors

 

1) Uranium Reactors are really U-235 reactors

 

Uranium is the only naturally-occurring material that can be used to make an atomic bomb or to fuel a nuclear reactor. In either case, the energy release is due to the fissioning of uranium-235 atoms in a self-sustaining “chain reaction”. But uranium-235 is rather scarce. When uranium is found in nature, usually as a metallic ore in a rocky formation, it is about 99.3 percent uranium-238 and only 0.7 percent uranium-235.  

 

Uranium-238, the heavier isotope, cannot be used to make an A-Bomb or to fuel a reactor. It is only the lighter isotope, uranium-235, that can sustain a nuclear chain reaction.If the chain reaction is uncontrolled, you have a nuclear explosion; if it is controlled, as it is in a nuclear reactor, you have a steady supply of energy. 

 

However, as the uranium atoms are split, the broken fragments form new smaller atoms called “fission products”. There are hundreds of varieties of fission products, and they are collectively millions of times more radioactive than the uranium fuel itself. They are the main constituents of “high-level radioactive waste” (or “irradiated nuclear fuel”) that must be kept out of the environment of living things for millions of years.

 

2) Thorium Reactors are really U-233 reactors

 

Thorium cannot sustain a nuclear chain reaction. Therefore it cannot be used to make a bomb or to fuel a nuclear reactor. However, if thorium is inserted into a nuclear reactor fuelled by uranium or plutonium, some of the thorium atoms are converted to uranium-233 atoms by absorbing stray neutrons. That newly created material, uranium-233, is even better than uranium-235 at sustaining a chain reaction.  That’s why uranium-233 can be used as a powerful nuclear explosive or as an exemplary reactor fuel.

 

So thorium cannot be used directly as a nuclear fuel.  It has to first be converted into uranium-233 and then the human-made isotope uranium-233 becomes the reactor fuel. 

 

Naturally, when uranium-233 atoms are split, hundreds of fission products are created from the broken fragments, and they are collectively far more radioactive than the uranium-233 itself – or the thorium from which it was created.  So once again, we see that high-level radioactive waste is being produced because of the use of thorium in the reactor. 

 

So, a so-called “thorium reactor” is really a uranium-233 reactor. And, as previously remarked, uranium-233 is a powerful nuclear explosive. Moreover, uranium-233 is immediately usable as a nuclear explosive, because the moment it is created it is very highly enriched – perfect for use in any nuclear weapons of suitable design.

 

3) Uranium-232 — A Fly in the Ointment

 

There is a complication that arises In the form of another human-made uranium isotope, uranium-232. In a thorium reactor, the uranium-233 that is created is accompanied by a very small quantity of uranium-232. As it happens, U-232 gives off very powerful gamma radiation that makes it difficult to fabricate an atomic bomb, given the danger to the workers and the heat generated by the intense radioactivity of U-232 and its decay products. But these difficulties can be overcome, or even avoided, by suitable adjustments to the reactor operation. 

 

Without going into too much detail, a thorium-232 atom normally  absorbs a neutron and is transformed into an atom of protactinium-233, which in turn is transformed into an atom of uranium-233. But if either of these two non-thorium atoms absorbs an additional neutron, before the conversion is complete, atoms of uranium-232 can be created – which act as unwanted pollutants. But if the protactinium atoms are removed from the reactor core as fast as they are produced, addition neutron collisions are prevented and an uncontaminated supply of uranium 233 can be obtained.

 

Is the Thorium-fueled "Molten Salt” Reactor a proven technology?

 

The first thorium-fueled molten salt reactor ever built was intended to power an aircraft engine in a long-range bomber armed with nuclear weapons. Despite massive expenditures, the project proved unviable as well as prohibitively costly and was ultimately cancelled by President Kennedy. The Oak Ridge team, under the direction of Alvin Weinberg, was allowed to conduct a thorium-fuelled molten salt reactor experiment for four years, during which time there were over 250 shutdowns, most of them unplanned.  The molten-salt thorium fuelled experience at Oak Ridge — the only such experience available to date — consumed about one quarter of the total budget of the enormous Oak Ridge nuclear complex. It is difficult to understand how anyone could construe this experience as demonstrating that such a technology would be viable in a commercial environment.

 

Summary:

 

It appears that thorium-fuelled reactors pose the same kinds of problems that existing nuclear reactors are afflicted with. Problems associated with the long-term management of nuclear waste, and the potential for proliferating nuclear weapons, are not qualitatively different even though the detailed considerations are not identical. Since a nuclear accident is caused by the unintended release of high-level nuclear waste into the environment, there is no qualitative difference there either. 

 

What about the dangers associated with mining a radioactive ore body to obtain the uranium or thorium that will be needed to sustain a uranium-based or thorium-based reactor system?

 

Thorium versus Uranium

 

Uranium and thorium are both naturally occurring heavy metals, discovered a couple of centuries ago. Uranium was identified in 1789. It was named after the planet Uranus, that was discovered just 8 years earlier. Thorium was identified in 1828. It was named after Thor, the Norse god of thunder.

 

In 1896, Henri Becquerel accidentally discovered radioactivity. He found that rocks containing either uranium or thorium give off a kind of invisible penetrating “light" (gamma radiation) that can expose photographic plates even if they are wrapped in thick black paper.

 

In 1898, Marie Curie discovered that when uranium ore is crushed and the uranium itself is extracted, the separated uranium is indeed found to be a radioactive substance, but the crushed rock contains much more radioactivity (5 to 7 times more) than the uranium itself. She identified two new elements in the crushed rock, radium and polonium – both much more radioactive than uranium and highly dangerous – and won two Nobel Prizes, one in Physics and one in Chemistry. 

 

Uranium Mining and Tailings

 

It turns out that 85 percent of the radioactivity in uranium ore is found in the pulverized residues after uranium is extracted, as a result of many natural byproducts of uranium called “decay products” or “progeny” that are left behind. They include radioactive isotopes of lead, bismuth, polonium, radium, radon gas, and others. Uranium mining is dangerous mainly because of the harmful effects of these radioactive byproducts, which are invariably discarded in the voluminous sand-like tailings left over from milling the ore. See www.ccnr.org/U-238_decay_chain.png .

 

Thorium Mining and Tailings

 

Thorium is estimated to be about three times more plentiful than uranium. Like uranium, it also produces many radioactive “decay products” or “progeny” – including radioactive isotopes of lead, bismuth, polonium, radium, radon gas, thallium, and others. See www.ccnr.org/Th-232_decay_chain.png . These byproducts are discarded in the mill tailings when thorium ore is milled.

 

Most of the naturally-occurring radioactivity found in the geological deposits of planet Earth are due to the primordial radioactive elements, uranium and thorium, and their many decay products. There is one additional primordial radioactive element, potassium-40, but it has no radioactive decay products and so contributes much less to the natural radioactive inventory.

 

I have written about thorium as a nuclear fuel several times before, beginning in 1978.

 

See www.ccnr.org/AECL_plute.html  and  www.ccnr.org/aecl_plute_seminar.html

 

Also see www.ccnr.org/think_about_thorium.pdf  and  www.ccnr.org/Thorium_Reactors.html

 

Gordon Edwards.

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