Thorium - A possible alternative energy source ?

[Phil Perry]

I have not read about Thorium in any depth, but this article piqued my interest when it mentioned that Australia contains the world's largest reserves of this material . . 16% of it according to the text. It says 'Part 2'. . and threatens a Third part,. . So I shall see if I can find part One, should it stir any interest or discussion at all on WUA. There are no 'Go To' embedded links within the text, just a mention of two leading people on the subject, in the last sentence.

 

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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.

 

 

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.

 

 

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.

 

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[old man emu]

Thorium fuel cycle - Wikipedia

 

70 cu ft ~ 2000 litres (D = 1400 mm; H = 1650 mm)

 

 

[Phil Perry]

Since everyone was so enthused by Part Two. . .. . .here is Part three. . .

 

 

 

 

 

As we’ve seen in the last chapter, there are two significant advantages of a molten salt reactor over the water boiling reactor range we have today: their fuel mix makes them inherently safer than water-cooled systems and they lend themselves to easy miniaturisation, which conventional systems do not.

 

Remember those futuristic looking ads in the 1950s for the atomic car? Or the nuclear reactor that would heat, chill and light your home? We used to laugh about them because we’ve grown up in a world where there was supposedly “no alternative” to the Uranium-235 cycle with light or heavy water as coolant and/or moderator and its resultant vast containment vessels.

 

This is down to the fact that with pressure remaining equal, water increases its volume by a factor 1,000 in case it evaporates, which it rather would once a light or heavy water reactor’s core went into meltdown (see Three Mile Island or Fukushima for reference).

 

Containment buildings for a molten salt reactor tend to be very, very small – they’re basically the size of the reactor itself. This appeared to make MSRs suitable for submarines and airplanes. In effect, the first proof of concept for this innovative technology was called the Aircraft experiment and it was initiated in 1946 by the US Air Force.

 

The ANP (Aircraft Nuclear Propulsion) project operated a 2.5 MW nuclear reactor small enough to fit on a strategic bomber and achieved 1,000 hours in service (although on the ground) in 1954. The military benefit of this technology during the Cold War was obvious: the elimination of any need for refueling intervals meant a strategic bomber fleet could be continuously airborne.

 

The reactor was joined to two General Electric J47 engines and the project ran the three prototypes HTRE (Heat Transfer Reactor) 1, 2, and 3 until being abandoned in 1957.

 

This same year, Pratt and Whitney started their Aircraft Reactor-1 at the Oak Ridge facility in Tennessee, but this was mainly an engineering test to see whether their product could withstand operating temperatures of around 680°C, which it did.

 

The first flight with an operating 3 MW nuclear reactor on board was the NB 36-H Nuclear Test Aircraft (NTA) in 1951. The main purpose of its then 47 sorties over Southern Texas and New Mexico was shield testing; the reactor couldn’t supply the aircraft with power for propulsion because any such technology was still years away.

 

The NTA spent 215 hours airborne, during which the reactor was operating for 89 hours. To shield the crew from radiation, the original flight deck was replaced by a lead-and-rubber-lined nose section that weighed 11 tons. Even the standard windows had to be replaced with ten-inch-thick lead glass.

 

The result of this testing and engineering effort was the USAF deeming it very dubious indeed whether any crew could be sufficiently shielded from radiation, ever. Along with all projects for nuclear aircraft propulsion, the ads for atomic cars and kitchens were quietly discontinued when JFK came into office.

 

All was not lost, because parallel to the USAF’s project, the National Laboratory at Oak Ridge, Tennessee, started its research in the new and innovative field of molten salt reactor technology.

 

Oak Ridge had already built the first practical light water reactor by the late 1940s (for use on US Navy ships and subs) and had designed portable reactors for the US Army in 1953, for use during deployment to remote locations were electricity, or indeed any energy supply was not a given.

 

All this rather changed with Kennedy, as all nuclear research was now to be presented as a gift to the world and the whole of mankind, in a rather ostentatious display of US leadership in all things moral. This early bout of virtue signalling led to the “Water for Peace” programme, and the molten salt reactor experiment was subsumed under this newer, kinder policy.

 

Research in light- and heavy-water U-235 technology continued apace, of course. This must have been down to the fact that the Thorium cycle rather doesn’t lend itself to the easy production of weapon grade Uranium or Plutonium because it produces large amounts of U-232, which is not fissile and must be chemically removed during enrichment in rather time consuming, complicated and inherently dangerous procedures.

 

In the eyes of the US military industrial complex, this killed the Thorium cycle stone dead. It became to be considered as of no practical use to the strategic defence efforts of the US and indeed the Western world, which by then ended a few short miles behind Brunswick, Germany.

 

I suppose it’s fair to assume that the battle against Communism had to be won at all costs, and could only be won with Plutonium production from U-235. If JFK’s bleeding-heard liberal propaganda effort could win it with “Water for Peace”, the US military wouldn’t stand in his way, as long as they could have enough Plutonium to wipe out mankind twice over.

 

This is probably the line of thinking that led to the molten salt experiment being subsumed under Kennedy’s propaganda efforts of presenting the USA as a gift to the world via “Water for Peace”.

 

The MSR was now meant to be a practical application that could power desalination plants in the Third World; and a very rational idea it was too, because desalination requires vast amounts of cheap energy, while in many parts of the world, clean and safe drinking water is much more of an urgent necessity than enough electricity to keep as many household appliances as possible running at once.

 

Besides, the need for running and maintaining the technology would draw its host nations into ever closer partnership with the US, which cannot have been an altogether undesirable effect.

 

 

Enter Alvin Weinberg, Director of Research of Oak Ridge National Laboratory, the brains behind the whole molten salt operation. Under his leadership, a 7.5 MW prototype was set up, run successfully for about three years on a mix of Lithium, Beryllium and Zirconium Fluorides, with the odd bit of Uranium Tetrafluoride as a source of nuclear energy thrown in.

 

The reactor went critical on U-235, but later its salt mix was partially shifted towards U-233 to prove that breeding Thorium-232 into U-233 would indeed produce a viable nuclear fuel source. The MSR at Oak Ridge had no facilities to breed U-233 from Thorium-232 on site. The piping and the reactor core were made from Hastelloy-N, a steel alloy especially produced for the nuclear industry.

 

The prototype operated for the net worth of 1.5 years during 1965 and 1969, while its liquid salt circulated in a continuous loop from the reactor to the coolant pump, to a heat exchanger, to the fuel pump and back to the reactor. In case of an emergency due to overheating, a Fluoride plug at the bottom of the reactor vessel would have molten, releasing all the liquid salt in to five separate underground storage tanks, where the chain reaction would have broken down instantly and the salt would have cooled off.

 

The MSR experiment got disbanded and Weinberg got fired during the Nixon years. Apparently, funding was already reduced towards the end of the 60s, with ORNL’s budget now going into particle acceleration, fusion research and of course the Apollo program, which promised much more bang for the buck propaganda wise than “Water for Peace” ever could, obviously.

 

No commercial application of the MSR was built, though in hindsight this would have been the next step towards introducing this novel kind of technology. So, in many regards, it is fair to say that Alvin Weinberg became a victim of his own success as well as a victim of the US military and industrial complex, which had partly enabled Weinberg’s success in the first place.

 

The other thought leader in the field besides Weinberg was an Indian gentleman named Homi J. Bhabha. In 1930, Bhabha got a first-class Mathematics degree at Cambridge where he studied under Paul Dirac, among other leading experts in their field. After the war, Bhabha returned to his native country and led the effort to supply the subcontinent with nuclear power.

 

This was an obvious aim, but in the case of India it meant making do with what you’ve got, and making the most out of it, too. Because India is rather poor in Uranium ore, yet rather rich in Thorium, the latter appeared to be the nuclear fuel of choice.

 

In a first phase, India would enter the field of nuclear power with reactors that ran on U-235, to later make the shift to fast breeder reactors which could also provide for the nation’s military needs. Once this was achieved, India would establish nuclear power generation based on the Thorium cycle, which Bhabha considered the obvious choice for all civilian applications of atomic power.

 

This “Three Stage Plan” previsioned a generation of 8,000 MW by the year 1980; current energy generation from nuclear sources is at around 3,300 MW p.a. in India.

 

Bhabha’s vision was far-fetched, overly optimistic and a bit too aspirational considering the realities on the ground, but it was vindicated nevertheless: India is currently operating the world’s only fast breeder reactor in Kalpakkam, near Madras (after the US, France, Britain and Germany have long given up on this technology), and India is ready to build a 300 MW reactor that will use Thorium as its main source of nuclear fuel, though not in an MSR but in an advanced heavy-water system based on a pressurised heavy-water design.

 

There are significant development efforts in the field of the MSR and/or Thorium breeding underway in China and Japan, while all European nations and the US have taken pretty much of a back-seat position towards the whole thing; they are after all heavily invested in “renewables”, and too sudden a change of tack might upset a few private and/or public finances.

 

Therefore, although its feasibility and practicality has been shown fifty years ago, and its practical benefits are about as convincing as they ever were, the MSR died at the hands of military planning during the Cold War, which considered the U-235 reactor a much better asset because it would breed enough Plutonium to produce all the bombs we would need to wipe out mankind twice over. The MSR became a lost case for the West. Other nations will reap its rewards, and rightly so.