Do thorium reactors prevent nuclear weapons proliferation risks?

Gordon Edwards, 30 June 24.

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.