The Thorium Cycle, Part Two

A question you may be asking yourselves now is: if there is a commercially viable application of the Thorium cycle, why haven’t I heard of it before? Well, there is a very simple and obvious answer to this: according to calculations from Canada and India, a kilowatt hour of electricity generated from Thorium will cost about three pence. That’s about a tenth of the current price of immensely subsidised “renewable” energy in the UK and much of Western Europe.

If a truly environmentally friendly energy became available at that price, it would quite totally upset the apple cart of the “green” industry along with its research grants and subsidised non-businesses.

As a whole, “renewables” rely heavily on the taxpayers’ largesse to be kept alive, along with all the “green” and “eco-friendly” investment bonds which are of course not environmentally friendly or socially acceptable at all, as we’ve already seen with regards to the appalling impact of rare earth mining and the increasing number of deaths from NOx pollution since “decarbonisation” began in earnest.

“Green” energy is killing people on an industrial scale already, and is thus most definitely not the way forward to provide for the energy needs of all of mankind. Unless of course one were of such an equally Malthusian and sanctimonious disposition that it bordered on the vile, and wanted humanity to perish. Yet, all the money going into Big Green can of course buy endless hours of favourable PR in the media.

It is probably right to assume that using fossil fuels for meeting the electricity demand of ten billion people globally won’t be possible with current technology because vast parts of the Earth would be suffering from an almost Victorian smog, as is today the case in many parts of China.

Efforts at “decarbonisation”, “CO2-extraction” and “carbon storage” may lead to technically viable solutions but would undoubtedly increase energy prices dramatically, with largely adverse effects on developed economies and their consumers (this may be the intended effect of “green” legislation, after all).

Unless a dramatically new source of energy is discovered by physicists, or by scientists in an adjacent field of study, this leaves us with only one option for the time being: nuclear power.

Guardian Council, Going Postal

We have seen in the first installment that the Thorium fuel cycle lends itself to energy generation from nuclear power: it is possible, but is it also practical? What are the specific advantages of this way of energy generation? Are there particular disadvantages, and if yes, which are they? And most importantly: what’s the trade-off between the upside and the downside if we want a safe and cheap power supply for ten billion people globally? How does the Thorium fuel cycle compare to other methods of energy generation?

Set against this background, Thorium is a much more obvious choice of an energy source than Uranium, or the even more arcane Plutonium. One ton of Thorium yields about the same amount of energy as 100 tons Uranium, or 3.5 million tons of coal. So it’s rather more economical to mine Thorium instead of coal or Uranium.

Thorium is about three to four times more abundant than Uranium in the Earth’s crust. There is enough Thorium in the USA and India to supply each country with energy for the next 1,000 years; obviously, a lot of fundamental research could happen during such a period.

Australia has the largest Thorium reserves of the world, close to 19 % of the element are located down under. The US, Turkey and India each control between 12 and 16 % of known world reserves. In these countries, Thorium often accounts for 12 – 14 % of top soil and it can be mined in open-pit operations.

Due to the structure of the Thorium cycle, there is very little Plutonium produced (about 1 % of the amount of Plutonium produced in the U-235 cycle). But more to the point: when fertile Thorium (Th-232) is converted into fissile Uranium (U-233), an almost equal amount of U-232 is produced, which makes the material rather useless for military applications.

It is a technically very complex and challenging procedure to separate U-232 from U-233, which makes the Thorium cycle rather immune to nuclear proliferation. Its residue is very hard to turn into weapon grade material.

Also, the Thorium cycle creates much less radioactive waste than the Uranium cycle: Western experts say that burning U-233 (from Th-232) will only produce 1 % of the waste of current reactors which are of course using the more conventional U-235. Quoting their practical experience, Chinese sources state a figure closer to one permille.

The resultant by-products of the nuclear chain reaction in a molten salt reactor stop being a threat to the environment after a one or a few hundred years, much earlier than the actenides produced in the U-235 cycle which remain radioactive for over 20,000 years.

Perhaps the most interesting aspect of Thorium is that it can be bred in to fissile U-233. When converted to Uranium Tetrafluoride (UF4), this U-233 can be mixed into an alkaloid cocktail of Lithium, Beryllium and Zirconium, all of which readily produce Fluoride compounds (due to Fluorides high reactivity with almost anything).

This mixture of Uranium and Alkaloid Fluorides is – for chemical reasons which we do not now need to go into – a salt with rather intriguing properties: it is highly heat absorbent and heat conductive, which makes it an effective coolant for any nuclear reactor.

It allows for very high operating temperatures (probably in a range beyond 800°C, where hydrolysis, or Hydrogen generation from water, becomes a distinct possibility). These thermic energies could apparently be controlled with 1960s’ technology as far as the engineering, piping and heat exchange part of a prototype was concerned.

But most importantly: once the salt mixture goes critical (i.e. the nuclear chain reaction starts) the salt mixture is self-regulating to an extent. It keeps the chain reaction within safe parameters almost by itself: when fission becomes too intense, heat goes up and the fuel mix expands – thus increasing the distance between the U-233 atoms and slowing the chain reaction down.

The fission in a molten salt reactor appears to be inherently self-stabilising to a large degree under normal operating parameters. And this is a material feature of the stuff itself and not by man’s design, so it cannot be easily tempered with. It won’t go wrong unless someone wanted it to go wrong.

The salt mixture that contains the fissile material is both the coolant and the moderator in a molten salt reactor – and it is at least to an extent a self-moderating coolant, too. It does not contain water, which means that there’s no need for huge containment spaces in case something went wrong.

The containment vessel of a conventional reactor must by laws of nature be 1,000 times more spacious than the reactor contained therein. Because water (its main coolant) must be able to expand by a factor of 1,000 when it vaporises if pressure is to remain equal – which it rather must, unless you’d like an explosion.

As there is no water circulating in a molten salt reactor, its containment vessel can be reduced to the size of the reactor itself. The prototype needed 70 cubic feet for 7.5 MW. This obviously has a very advantageous effect on site selection as well as building and maintenance costs of any such power plant.

And, to round it off, when run on closed circuit air turbines, the heat to power ratio of a molten salt reactor reaches up to 46 % efficiency – which is significantly higher than the water boiling reactors of current design which can reach between 32 and 36 % energy efficiency.

Guardian Council, Going Postal

Now, along with these significant advantages there must be some disadvantages too, or so one would assume. And this is indeed the case.

Continuous operating temperatures in the range of 500 or 600°C along with irradiation by highly aggressive gamma rays in the reactor’s core put significant stresses on all materials. It was yet possible in the 1960s to produce a steel alloy that withheld them. That further R&D would have improved on this picture, is fair to assume.

Another significant challenge is that fission of U-233 creates a host of by-products which must be tightly controlled and removed from the molten salt mix for the reactor to remain operational. Some of these by-products are noble gases such as Xenon, which after building up to a certain level will slow the chain reaction down and therefore must be removed constantly.

The prototype also encountered challenges in the form of a gradual build-up of other, non-gaseous noble elements in the reactor, which had to be physically removed during regular maintenance intervals. Most importantly, though there are only a hundredth or a thousandth of them, there are of course radioactive nucleotides created in a molten salt reactor too which must be removed from the mix and handled on site before safe disposal (for a forty times shorter period of time than the residue of conventional U-235 reactors).

The research team that ran the prototype of a molten salt reactor between 1963 and 1969 considered all these challenges significant, but ultimately surmountable with 1960s technology, so I suppose it is safe to assume that there is a practical possibility of this technology being made to work today.

The next installment will look at the question “if they’re that good, why don’t we have them already?”. And we’ll finally take a look at the historical and ongoing efforts of building and running a molten salt reactor and/or a Thorium cycle, presented through the two thought leaders in this field, Alvin Weinberg and Homi J. Bhabha.
 

© Guardian Council 2018