Question: What do you think about “alternative” nuclear technologies”?

Question mark #2Have you ever looked at “alternative” nuclear technologies, for example molten salt reactors (or liquid fluorides as today are termed)? For example, see Mechanical Engineering: Too Good to Leave on the Shelf. One of the author’s argument is that the technology is pratically available today, and almost all of the R&D need has been already spent. Not only a MSR need only a fraction of the uranium of “traditional” reactors, but pratically produces no long lifes waste (plutonium and other transuranics)and has incredible features of “passive” safety.

From the article:

MSRs run at low pressures and so don’t need the large pressure vessels common in today’s reactors. They can run on a variety of fuels and can even burn transuranic waste produced at other reactors. More intriguingly, molten salt reactors can be designed to breed their own fuel without the need for off-site processing.

Molten salt reactors (sometimes referred to as liquid fluoride reactors) contain no fuel pellets. Instead, the fissile and fertile materials are dissolved in a fluid medium. The fluid can be one of various fluorides of uranium, thorium, or plutonium, which form low melting point eutectics when combined with certain carrier salts such as 27LiF-BeF2, which is known as flibe. When raised above the melting point (some 460°C) this mixture becomes a very stable liquid that can flow continuously between a simple core (typically containing graphite moderator) and external heat exchangers. Heat from the radioactive primary salt is transferred to a clean intermediate salt that then transfers heat to either a steam or gas cycle.

Molten fluoride salts are excellent coolants, with a 25 percent higher volumetric heat capacity than pressurized water-and nearly five times that of liquid sodium. That greater heat capacity results in more compact primary loop components like pumps and heat exchangers. Molten salt reactors run at near-atmospheric pressure, so the thick-walled pressure vessels found in light-water reactors is unnecessary. Since there is no water or sodium in the reactor fluids, there is zero possibility of a steam explosion or hydrogen production within the containment.

MSR designs have very strong negative temperature and void coefficients, which act instantly, aiding safety and allowing automatic load following operation. Also, the fluid nature of the fuel means meltdown is an irrelevant term. In the case of emergency, the fuel salt is automatically drained to passively cooled, critically safe drain tanks. Any salt temperature above normal simply melts a frozen plug of salt like pulling the plug on a bathtub.

Fissile material concentrations within an MSR are easily adjusted on a continuous basis. Such adjustments eliminate excess reactivity and the need for burnable poisons, which is common in solid-fuel reactors. Also, many fission products quickly form stable fluorides that will stay within the salt during any leak or accident. Others are volatile or insoluble and can be passively and continuously removed. Xenon gas, which represents almost half of all neutron absorptions to fission products in most solid-fuel reactors, will just bubble out of the fuel salt and can be stored outside the reactor loop.

Some of the fission products must remain isolated for several hundred years, but there is no need for Yucca Mountain-type repositories intended to last millennia. It is plutonium and the other transuranic elements of light water reactor spent fuel that are the real issue. MSRs produce them at much lower rates and recycle them, thus the long-lived radiotoxocity of MSR waste is one-ten-thousandth that of an LWR.

There are many design variations, which can be grouped into two main categories. Breeder reactors produce their own fissile fuel after startup. The typical plan for a breeder is to start with fertile thorium, which after capturing a neutron decays to fissile uranium-233. This cycle is capable of being a breeder in softer neutron spectrums where neutrons are slowed down, typically by graphite; the familiar breeding cycle that converts uranium to plutonium requires a harder or faster neutron spectrum. The reactors don’t have to be breeders, or be limited to a thorium cycle. Without fuel processing, MSRs can run as simple converters with excellent uranium utilization even on a once-through cycle. Converter designs, which require annual additions of fissile material, can run excellently off even low-enriched uranium. Converters and breeders each offer advantages, and the main point of difference between the two is whether fission products are actively processed out of the salt during operation.


The amount of fissile material needed to start new reactors is also very important, especially in terms of a rapid fleet expansion. The 1 GWe DMSR was designed for 3.5 metric tons of U-235 (in easy-to-obtain low-enriched uranium) which can be lowered if uranium costs go up. A new PWR, by contrast, needs about 5 metric tons, whereas a sodium-cooled fast breeder such as the PRISM design requires as much as 18 tons of either U-235 or spent fuel plutonium. Any liquid fluoride reactor can be started on plutonium as well, but this turns out to be an expensive option, since removing plutonium from spent fuel costs around $100,000 per kilogram.

From the same author and topic, see Liquid Fluoride Reactors: A Luxury of Choice, in particular slide 23 “simplified liquid fluoride converter reactors …. Almost no R&D to build now”.

See also:

Alessandro De Maida, 28 May 2010


Thank you.  My overall view is that we need nuclear generation as a bridge technology until we can be 100% reliant on renewables.  This means that it is sensible to standardise and stick to existing, known designs, in order to keep costs down.  This has been the French approach, whereas in the UK, each new reactor has been a bit different, so more expensive.
However, the main danger of nuclear power is weapons proliferation, and thorium reactors are much less of a proliferation risk. They may also in future be able to help deal with existing nuclear waste and plutonium.  So I think that thorium reactors are the exception to the standardisation rule, and that countries hoping to develop thorium reactors, such as India, should be supported.

Stephen Tindale, 28 May 2010



  1. Dear Sir,
    At a parallel session to COP15 December 2009 in Copenhagen I and 3 others (GLOBAL ALARM ASSOCIATION) presented a MiniCOP resolution with 4 factors, which could save the climate: 1. UN Human Responsibilities, 2. Family Planning, 3. Reforestation, 4. Thorium Energy. The resolution is cost-benefit neutral and can be seen on website
    The MiniCOP resolution has also been sent to many political leaders, which apparently consider the economy more important than the climate. They are focused on CO2 quotas where the rich countries can emit more CO2 if the poor countries emit less – and secondly the climate adaptation, which does not solve the problem. The people of Tuvalu and other inhabitants of islands in the Pacific cannot adapt to the climate change while their islands disappear in the ocean.
    The politital leader are not listening to common sense!!
    Jonna Vejrup Carlsen
    Strandvejen 120 D
    DK-8000 Aarhus C, Denmark

  2. Alessandro De Maida

    I don’t know if this thread is still active…

    More recently doct LeBlanc gave an other presentation at Oak Ridge, video and slides are available here

    I do note that, according to LeBlanc, a MSR breeder consumes only one tonn of thorium per year (per GWe installed) while an high efficiency MSR converter needs only 15 to 35 tonn at max of natural uranium (against 150-250 tonn per GWyear for LWR or Candu). A “converter DMSR” can even reduce Earth radioactivity after only 300 years and produce less or the same transuranics wastes than a pure thorium/uranium cycle reactor (but being much more simple and easy to develop in the short term)

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