The more effective, the smaller and the safer the new nuclear power plants become, the louder the cries of Cassandra sound against the horrors of the atom. Even if the reactors convert nuclear waste into energy, the engineers are sure to be rejected. Yet there are ingenious developments such as the dual-fluid reactor - which is now probably being built in Rwanda.
by Udo Pollmer July 18, 2024
As many as 85,000 participants travelled to the Climate Change Conference in Dubai in December 2023, including more than...
...150 heads of government from all over the world. There, the global climate policy authorities came to a surprising realisation: splitting atoms does not produce CO2 ! The joint expansion of nuclear technology was therefore decided on the spot. The launch workshop took place in Brussels at the end of March 2024.1
"As chance would have it," nuclear physicist Hofmann-Reinecke suspects, "the licence to demolish the last remaining operational nuclear power plant 'Isar 2' was granted in Germany at exactly the same time as the Brussels conference. In this case, the bureaucracy worked relatively quickly ... so that it [the reactor] could not be revived in the event of a possible U-turn in energy policy."1
He continues: "March 2024 will go down as a fateful date in German history. It is the point in time when it became clear how the land of poets and thinkers, the country where the fission of the atomic nucleus was discovered, left the family of civilised states and embarked on a very dark path downhill."1
The molten salt reactor
Which path will mankind now take to secure its energy supply? In any case, fast breeder reactors will play an important role for the foreseeable future. Probably the most popular is the molten salt reactor. In principle, this consists of a container with hot liquid salts in which a nuclear reaction takes place. The molten salt, usually fluorides or chlorides, contains the fuel. The whole mixture is also a coolant, it is chemically inert and non-flammable.
In conventional reactors that use fuel rods or spheres, 96 % of the energy remains unutilised. The resulting fission products then slow down the nuclear reaction. Only reprocessing allows them to be utilised again. Reactors with liquid fuel are different. Fission products are also produced here. However, unlike fuel rods, these are easier to separate from the liquid. This means that the fuel can be used for much longer.
If desired, old nuclear waste can also be burnt in the molten salt reactor. It reliably fissions risky transuranium elements such as plutonium. This should also improve performance because there are sufficient suppliers of neutrons in the waste to produce fissile uranium-233 from thorium-232. New fuel is added as required without the reactor having to be shut down.
"Boiling over" is physically impossible with molten salt operation. The reactor is not pressurised and contains no water. There is nothing that could cause an explosion. There is no danger of a core meltdown with molten salt, as the fuel is always liquid.2 The reactor transfers its energy to another liquid salt circuit in the first heat exchanger. This then transfers the heat to the steam generator, which produces electricity using a turbine.
What happens if the cooling fails? Then the laws of physics take effect, in this case the aforementioned negative temperature feedback. Because the salts mentioned expand massively when heated, the hit rate of the neutrons decreases, the fission rate drops and the reactor cools down. If the salt contracts during cooling, nuclear fission increases again and more energy is generated.3 Catastrophic accidents such as those in Chernobyl or Fukushima are thus prevented by natural law - without the need for complex safety systems.
As a last resort, there is a "plug" at the bottom of the reactor, which is cooled down with the electricity generated. If the power fails in the event of an accident, the plug melts: The radioactive slurry runs into tanks to fall below the critical mass. There, a chain reaction is no longer possible.3
Technical challenges
Every type of energy generation has its pitfalls, whether wind turbines, geothermal energy or reservoirs. In the case of molten salt reactors, tritium must be mentioned because it poses a risk to personnel.4 Although this type of reactor works without water, the amount of tritium released is significantly higher than in pressurised water reactors.5 The gas is produced in the salt solution by neutron bombardment of lithium and beryllium. Like ordinary hydrogen, it diffuses through metals of all kinds.3,6 Storage media are now available that absorb tritium, e.g. on the basis of depleted uranium-238.7 New permeators are also being developed to capture the tritium in the melt.8
Another technical challenge was the corrosion caused by the molten salt. Since, in contrast to the light water reactor, no oxide layer forms on the surface, corrosion has so far been slowed down by cleaning the salt, controlling the redox potential and using buffers.9 In the meantime, a mixture of lithium and beryllium fluoride (Li2[BeF4]) has become established, which is hardly corrosive at all. Critics argue that beryllium is quite toxic.9 However, it has long been used routinely in the aluminium industry and in mechanical engineering. So far, nobody has been bothered by this.
Small is beautiful
Work on molten salt reactors is now underway all over the world. The first reactor of this type, the Chinese TMSR-LF1, received its operating licence in 2023.10 Like pebble bed reactors, molten salt reactors are to be installed on a decentralised basis in order to supply remote parts of the country or the sparsely populated deserts and steppes of western China with energy. In arid regions, reactors that do not require a river to supply cooling water are advantageous. The TMSR-LF1 does not initially supply any electrical energy, but only heat or steam for the industrial plants there. The whole ensemble is not located in the Gobi Desert, the coldest desert in the world, for nothing.11
The transport industry is now also taking a liking to it. At the end of 2023, Chinese shipbuilder CSSC presented its project for a container ship powered by a molten salt reactor in Shanghai. There have already been merchant ships with light water reactors such as the "Otto Hahn". They were decommissioned or converted to diesel because harbours refused entry.12 However, nuclear-powered aircraft carriers, icebreakers and submarines have been in service for decades. They come into the shipyard for an overhaul every 20 years or so. There, the entire reactor module is lifted out and replaced with a new one.
The day when container ships enter harbours around the world quietly and with zero emissions is drawing closer: US companies Southern Company and TerraPower recently began extensive tests for a new ship reactor, and now Hyundai Heavy Industries, one of the largest shipbuilding groups, has joined the molten salt project.13 This has been followed by partnerships with European companies such as Naarea and Thorizon for the construction of modular molten salt reactors for the incineration of nuclear waste.14 Almost at the same time, Rosatom announced that the research had been successfully completed and that the Russian nuclear agency was now planning to build such a power plant.15
As "nuclear batteries", modular fast breeders are intended to provide a continuous supply of energy for 15-20 years.16 Conventional batteries can only compensate for a brief power outage. A nuclear battery allows the population to be continuously supplied with food even in the event of crises and disasters. It can be used to keep refrigeration systems running and to heat the ovens in baking lines.
The modular design allows such reactors to be combined into larger units. Modules can be industrially pre-produced in large quantities and transported to the place of use, which significantly reduces costs. Exporting them would not only fill the state coffers, but would also bind these countries to China, for example through maintenance contracts. At the same time, raw materials that China's industry needs could be secured.
The hour of mourners
The eco-scene dutifully sees black. The Swiss Energy Foundation laments: "There are still no comprehensive safety analyses for the MSR (Molten Salt Reactor) .... The reactor is still decades away from commercial operation."17 Deutsche Umwelthilfe e.V. seconds: "In addition, this technology is still in the research phase and is not yet fully developed, let alone commercially viable".18 According to the Öko-Institut e.V., "at present there is no clear advantage or disadvantage" of molten salt reactors compared to light water reactors "with regard to reactivity control, cooling and residual heat removal and the containment of radioactive substances".19
It's funny: the fact that this reactor will usefully dispose of nuclear waste doesn't seem to impress those experts who constantly warn against nuclear waste. Rather, their writings give the impression that there is a vital interest in cultivating fear for as long as possible and blocking solutions. Tens of billions are spent year after year on the treatment and storage of nuclear waste and on the "nuclear phase-out", instead of using a fraction of the capital to eliminate it.
To generate 1 gigawatt of power, a coal-fired power plant burns around 800,000 tonnes per year. By comparison, an old-fashioned light water reactor requires around 100 to 200 tonnes of fuel rods per year. The current record is held by the dual-fluid reactor, a further development of the molten salt reactor: it requires just over one tonne of fuel for the same electrical output. To better visualise this: Due to the high density, this is a cube with an edge length of 40 centimetres.20
The combustion residue is correspondingly minimal. Of course, modern reactors also produce "nuclear waste", but this is a mere flyshit compared to previous power plants. In addition, modern reactors utilise the fuel much more effectively, so that the amount of residue is also lower. Of course, it is still possible to complain about "radiation hazards", even if the quantity and storage period are reduced by a factor of 100.
The dual fluid reactor
In this respect, the dual-fluid reactor is the most promising of the fast breeder reactors: A reactor block with a volume of a few cubic metres generates as much electricity as a large coal or gas-fired power plant. Compared with "wind farms", the amount of space required is ridiculously small. Compared to conventional molten salt reactors, its burning time is many times longer due to the simple and continuous separation of fission products. Thanks to its small footprint, the reactor can be housed in an underground bunker, making it both earthquake-proof and able to withstand aircraft crashes.21
A decisive difference to molten salt reactors is that fuel and coolant are separated from each other in dual-fluid reactors. The fuel flows inside tubes, past which the coolant, liquid lead, flows on the outside. Because the fuel does not contain any "melting salts", it can be more easily freed from fission products. In the dual fluid recycling plant, old fuel is first converted into liquid salt and then separated into its components by distillation. This process has long been established outside the nuclear industry. All fissile materials are mixed with fresh fuel and fed back into the reactor, where they generate energy or are converted into short-lived isotopes.22
Since fast breeder reactors "chop up" the fissile materials much more, they also produce more small molecules, i.e. volatile gases, some of which emit radiation. Most of them, such as iodine-131, are short-lived. In addition, there are gases such as xenon and krypton, which reduce the efficiency of the reactor.23 They are all flushed out with the help of the noble gases helium or argon and transferred to a separate tank in order to utilise their decay heat.20 Half-lives of a few months at most mean that their activity decreases rapidly.
Further separation is carried out by pyrochemical distillation.24 Fission products that are no longer usable and have half-lives of up to several decades are separated by element. Due to their small quantity, they can be stored in a modest bunker on the company premises. Within 100 years, 90 per cent of the elements can be sold by type as rare earths. The rest will only be "ripe" for harvesting after 300 years. This enables almost complete utilisation in the long term, creating a genuine circular economy for the first time.25
What happens in the event of accidental misuse or sabotage? The same as with normal molten salt reactors, the negative temperature feedback takes effect: when the fuel liquid heats up, it expands. The so-called Doppler spread of the atoms has the same effect. As a result, energy production decreases and the temperature drops.26 The liquid lead further intensifies the feedback effect.21 As a result, the system acts like a thermostat: the reactor keeps its temperature constant at 1,000°C. This enables it to follow the load automatically. It adapts to the respective electricity demand, an extremely important capability: this means that the strong fluctuations in energy from wind and sun can be compensated for without having to keep coal-fired power plants on standby.27
The Dual Fluid is an undemanding "omnivore". In principle, any isotope with an atomic weight of thorium upwards is suitable. This includes nuclear waste, natural uranium, depleted uranium and nuclear weapons. With its working temperature of 1,000°C, even hydrogen electrolysis from water appears economical for industrial purposes, as does the production of synthetic fuels. The compact design, which requires very little material, makes it possible to use expensive, particularly stable materials such as tungsten, tantalum or silicon carbide.
Looking ahead
Dual fluid is now regarded as the most efficient of all energy sources. It was primarily invented by Armin Huke, then Managing Director of the Institute for Solid State Nuclear Physics in Berlin. For Germany, once a leader in this new technology, development has run its course. Because the Germans never want to use nuclear power again, the company decided to relocate its headquarters to Canada in 2021. So far, the reactor only exists on paper - as is usual with groundbreaking inventions. A first test reactor is built in Rwanda.
And Germany? Old coal-fired power stations with poor efficiency levels are being reactivated, producing enormous amounts of pollutants including radionuclides. Those who can't afford this expensive luxury electricity will cook their eco-food from wild harvests with a clear conscience and in harmony with nature over an open fire on a rubbish bin! How delicious is the feeling of "ethical" superiority after we give up our technological foundations of life with great jubilation.
Conclusion
These were selected examples from a wide range of solutions to the nuclear waste and energy problem. Now that it would be possible to dispose of this waste as far as possible, the generation to which the "radiating legacy" is owed should now do its part. It is a technical stroke of luck that a great deal of energy can still be generated.
Does this mean that nuclear power is finally "harmless" and "safe"? No, any more than a kitchen knife or a dam. Not all the physical effects at work in the reactor are yet known. One example is cold fusion, which was once ridiculed and is now taking centre stage in nuclear research. Perhaps there are other and even better ways of generating energy.
The fact that the elegant disposal of the legacy of the nuclear industry is possible today is thanks to the engineers in this very industry. Those critics who have blocked the trialling of solutions for decades with the audacious argument that they have not yet been tested are not worthy of respect. Wind, solar and hydrogen will not be able to reliably supply urban societies with food in the foreseeable future.
References
01) Hofmann-Reinecke H: Deutschlands nukleare Geisterfahrt. Think-again-Blog vom 30. März 2024
02) Elsheikh BM: Safety assessment of molten salt reactors in comparison with light water reactors. Journal of Radiation Research and Applied Sciences 2013; 6: 63-70
03) IAEA: Status of Molten Salt Reactor Technology. Technical Reports Series 489, Wien 2023
04) Zohuri B et al: Heat-pipe heat exchangers for salt-cooled fission and fusion reactors to avoid salt freezing and control tritium: a review. Nuclear Technology 2020; 206: 1642–1658
05) Zeng Ys et al: A simulation study of tritium distribution in a 10WM(e) thorium-based molten salt reactor. Annals of Nuclear Energy 2024; 197: e110272
06) Schmutz H et al: Tritium formation and mitigation in high temperature reactors. INL/EXT-12-26758, Idaho National Laboratory, 2012
07) RC Tritec AG: Tritiumspeicher: Sichere and praktische Aufbewahrung von Tritiumgas. Retrieved 14. April 2024
08) Zeng Ys et al: A simulation sturdy of tritium removal from molten salt at high temperature with tritium permeation through metallic material. Annals of Nuclear Energy 2022; 170: e108977
09) Roper R et al: Molten salt for advanced energy applications: A review. Annals of Nuclear Energy 2022; 169: e108924
10) Wang B: China thorium molten salt experimental reactor is licensed for operation. Nextbigfuture.com 15. June 2023
11) Mallapaty S: China prepares to test thorium-fuelled nuclear reactor. Nature 2021; 597: 311-312
12) Posch M: China’s nuclear-powered containership: a fluke or the future of shipping? Hackaday.com 26. Dec. 2023
13) Dixon G: Nuclear power for shipping takes a step forward with the help of the world’s largest shipyard. TradeWinds 5. Feb 2024
14) Anon: Naarena and Thorizon team up on molten salt reactors. World Nuclear News 12. Feb. 2024
15) Anon: Preliminary design R&D completed for Russian molten salt research reactor. World Nuclear News 5. Feb. 2024
16) OECD: The NEA Small Modular Reactor Dashboard: Volume II. OECD 2023, NEA No. 7657
17) Schweizerische Energie-Stiftung: Faktenblatt – Neue Atom-Reaktoren. Juli 2015
18) Scheer SS, Walter J: Atomkraft? Immer noch: Nein Danke! Mythen über Atomenergie und die neue AKW-Generation. Deutsche Umwelthilfe, April 2022
19) Pistner C et al: Sogenannte „neuartige“ Reaktorkonzepte. Öko-Institut e.V., Darmstadt 10.3.2023 in: Bundesamt für die Sicherheit der nuklearen Entsorgung: Analyse und Bewertung des Entwicklungsstands, der Sicherheit und des regulatorischen Rahmens für sogenannte neuartige Reaktorkonzepte. Zwischenbericht zu AP-1 und -2; Vorhaben 4721F50501
20) Schwarzenberg M: Neue Entwicklungen bei der Nutzung von Kernenergie. Naturwissenschaftliche Rundschau 2019; 71: 291-294
21) Lewitz JC et al: The dual fluid reactor – an innovative fast nuclear-reactor concept with high efficiency and total burnup. Atw. Internationale Zeitschrift fuer Kernenergie 2020; 65: 145-154
22) Dual Fluid: Reinventing Nuclear. Whitepaper: Kernkraft der fünften Generation von Dual Fluid. Dual Fluid Energy Inc. 2022
23) Zhou B et al: Study on kinetic characteristics of Krypton and Xenon radioactive source term in molten salt reactor. EPJ Web of Conferences 2020; 239: e22005
24) Rodriguez D et al: Pyrochemical reprocessing of molten salt fast reactor fuel: focus on the reductive extraction step. Nukleonika 2015; 60: 907-914
25) Huke A et al: The Dual Fluid Reactor – A novel concept for a fast nuclear reactor of high efficiency. Annals of Nuclear Energy 2015; 80: 225–235
26) Sierchuła J et al: Negative temperature coefficients of reactivity for metallic fuel dual fluid reactor. Progress in Nuclear Energy 2022; 146; e104126
27) Huke A et al: Der Dual-Fluid-Reaktor und die Möglichkeiten der Kernenergie. In: Schluss mit der Klimakrise. Edition Novo 2020, Nr. 131: 84-103
English Editor: Josef Hueber
