Back to the Dream Factory
by Gordon Edwards, July 13, 2011
The Nuclear Dream Factory
Every time a nuclear power reactor idea doesn't work out, and ordinary people get down-hearted and start to doubt the magnificence and benificence of nuclear energy, nuclear proponents rush back to their well-stocked dream factory to fetch another idea -- one that is sufficiently unfamiliar and sufficiently untested that ordinary people have no idea whether it is good or bad, safe or dangerous, feasible or foolish, or whether the almost miraculous claims made about it are true or false.
Just a few years ago, nuclear proponents were pushing Generation 3 reactors -- enormous plants that would generate huge amounts of electricity, yet be cheaper and faster to build than earlier models, as well as being safer and longer-lived.
Then Areva ran into a blizzard of problems trying to build one of these behemoths in Finland -- the cost soaring by billions, the construction time stretched by years, and fundamental safety-related design problems surfacing late in the game. Check and mate.
Undaunted, nuclear proponents quickly executed a 180-degree turn and are now promoting small reactors which can be mass-produced by the thousands and sprinkled on the landscape like cinnamon on toast. Pebble-bed reactors, molten-salt reactors, thorium reactors, have been paraded before the public with as many bells and whistles as the nuclear industry can muster, to distract people's gaze away from the construction fiascos, the litany of broken promises from the past, the still-unsolved problems of nuclear waste and nuclear weapons proliferation, and the horror that is Fukushima.
The following paragraphs are written to dispel some of the mystique surrounding the idea of "thorium reactors" -- a very old idea that is now being dressed up in modern clothes and made to seem like a major scientific breakthrough, which it is not.
Thorium is not a nuclear fuel
The fundamental fact about thorium is that it is NOT a nuclear fuel, because thorium is not a fissile material, meaning that it cannot sustain a nuclear fission chain reaction.
In fact the ONLY naturally occurring fissile material is uranium-235, and so -- of necessity -- that is the material that fuels all of the first-generation reactors in the entire world. Thorium cannot replace uranium-235 in this regard. Not at all.
Thorium is a "fertile" material
But thorium-232, which is a naturally occurring radioactive material, is about three times as abundant as uranium-238, which is also a naturally occurring radioactive material. Neither of these materials can be used directly as a nuclear fuel, because they are not "fissile" materials.
However, both uranium-238 and thorium-232 are "fertile" materials, which means that IF they are placed in the core of a nuclear reactor (one that is of necessity fuelled by a fissile material), some fraction of those fertile atoms will be transmuted into man-made fissile atoms.
Some uranium-238 atoms get transmuted into plutonium-239 atoms, and some thorium-232 atoms get transmuted into uranium-233 atoms.
Both plutonium-239 and uranium-233 are fissile materials which are not naturally-occurring. They are both usable as either fuel for nuclear reactors or as nuclear explosive materials for bombs.
(The USA exploded an atomic bomb made from uranium-233 in 1955.)
Reprocessing of irradiated nuclear fuel
In general, to obtain quantities of plutonium-239 or uranium-233, it is necessary to "reprocess" the irradiated material that started out as uranium-238 or thorium-232. This means dissolving that irradiated material in acid and then chemically separating out the fissile plutonium-239 or uranium-233, leaving behind the liquid radioactive wastes which include fission products (broken pieces of split atoms, including such things as iodine-131, cesium-137, strontium-90, etc.) and other radioactive waste materials called "activation products" and "transuranic elements".
Reprocessing is the dirtiest process in the entire nuclear fuel chain, because of the gaseous radioactive releases, liquid radioactive discharges, and large quantities of highly dangerous and easily dispersible radioactive liquids. Reprocessing also poses great proliferation risks because it produces man-made fissile materials which can be incorporated into nuclear weapons of various kinds by anyone who acquires the separated fissile material.
Advanced Fuel Cycles and Breeders
Any nuclear reactor-fuelling regime that requires reprocessing, or that uses plutonium-239 or uranium-233 as a primary reactor fuel, is called an "advanced fuel cycle". These advanced fuel cycles are intimately related with the idea of a "breeder" reactor -- one which creates as much or more fissile material as a byproduct than the amount of fissile material used to fuel the reactor. So it is only in this context that thorium reactors make any sense at all -- like all breeder concepts, they are designed to extend the fuel supply of nuclear reactors and thus prolong the nuclear age by centuries.
The breeder concept is very attractive to those who envisage a virtually limitless future for nuclear reactors, because the naturally occurring uranium-235 supply is not going to outlast the oil supply. Without advanced fuel cycles, nuclear power is doomed to be just a "flash in the pan". Thorium reactors are most enthusiastically promoted by those who see "plutonium breeders" as the only other realistic alternative to bring about a long-lived nuclear future. They think that thorium/uranium-233 is a better fate than uranium/plutonium-239. They do not see a nuclear phaseout as even remotely feasible or attractive.
"Molten Salt" reactors
Molten salt reactors are not a new idea, and they do not in any way require the use of thorium -- although historically the two concepts have often been linked. The basic idea of using molten salt instead of water (light or heavy water) as a coolant has a number of distinct advantages, chief of which is the ability to achieve much higher temperatures (650 deg. C instead of 300 deg. C) than with water cooled reactors, and at a much lower vapour pressure. The higher temperature means greater efficiency in converting the heat into electricity, and the lower pressure means less likelihood of an over-pressure rupture of pipes, and less drastic consequences of such ruptures if and when they do occur.
Molten salt reactors were researched at Oak Ridge Tennessee throughout the 1960s, culminating in the Molten Salt Reactor Experi- ment (MSRE), producing 7.4 megawatts of heat but no electricity. It was an early prototype of a thorium breeder reactor, using uranium and plutonium as fuels but not using the thorium blanket which would have been used to "breed" uranium-233 to be recovered through reprocessing -- the ultimate intention of the design.
This Oak Ridge work culminated in the period from 1970-76 in a design for a Molten Salt Breeder Reactor (MSBR) using thorium as a "fertile material" to breed "fissile" uranium-233, which would be extracted using a reprocessing facility.
Molten Salt Thorium reactors without reprocessing?
Although it is theoretically possible to imagine a molten-salt reactor design where the thorium-produced uranium-233 is immediately used as a reactor fuel without any actual reprocessing, such reactor designs are very inefficient in the "breeding" capacity and pose financial disincentives of a serious nature to any would-be developer. No one has actually built such a reactor or has plans to build such a reactor because it just isn't worth it compared with those designs which have a reprocessing facility.
Here's what Wikipedia says on this matter (it happens to be good info):
To exploit the molten salt reactor's breeding potential to the fullest, the reactor must be co-located with a reprocessing facility. Nuclear reprocessing does not occur in the U.S. because no commercial provider is willing to undertake it. The regulatory risk and associated costs are very great because the regulatory regime has varied dramatically in different administrations. UK, France, Japan, Russia and India currently operate some form of fuel reprocessing.
Some U.S. Administration departments have feared that fuel reprocessing in any form could pave the way to the plutonium economy with its associated proliferation dangers.
A similar argument led to the shutdown of the Integral Fast Reactor project in 1994. The proliferation risk for a thorium fuel cycle stems from the potential separation of uranium-233, which might be used in nuclear weapons, though only with considerable difficulty.
Currently the Japanese are working on a 100-200 MWe molten salt thorium breeder reactor, using technologies similar to those used at Oak Ridge, but the Japanese project seems to lack funding.
Thorium reactors do not eliminate problems
The bottom line is this. Thorium reactors still produce high-level radioactive waste, they still pose problems and opportunities for the proliferation of nuclear weapons, they still pose catastrophic accident scenarios as potential targets for terrorist or military attack, for example.
Proponents of thorium reactors argue that all of these risks are somewhat reduced in comparison with the conventional plutonium breeder concept. Whether this is true or not, the fundamental problems associated with nuclear power have by no means been eliminated.
Gordon Edwards, Ph.D., President,
Canadian Coalition for Nuclear Responsibility.