DUAL FLUID | REACTOR TECHNOLOGY


20 Start-up T y


023


2023 Component tests TRL* 3 (10 years of groundwork done) o TRL 4 R


2 28 2028 Test plant Test plant design TRL 5 L TRL 6L TRL 6


construction and operation


TRL 7 TRL 7 TRL 8 TRL 8


2


2031


Pre-serial production


TRL 9 TRL 9 Other products Prototype Prototypep Dual Fluid 300 Dual Fluid 300 a Serial production


Left, figure 6: Possible timeline to serial production * Technology readiness level


1 Seed round e n Investment rI e ounds** n IPO** Investment rounds** m u


decarbonised within 15 years


ower grid c 15 year


e grid could be r


co d


rs Power ** Forecast


the energy return on investment for Dual Fluid with that of other power sources.


Material issues The material separating the two fluids of the Dual Fluid reactor must have sufficient thermal conductivity and corrosion resistance, both for the lead and for the fuel – which is also a molten liquid metal. Compared to the conditions in thermal reactors, there is a wide choice of materials for the structural walls mainly because of the low neutron capture cross sections for fast neutrons. Materials that are suitable in principle have in fact existed for decades, but they contain rarer and more expensive chemical elements. This may be a problem for conventional reactor technology and for modern molten salt concepts since they require large quantities of structural materials due to relatively low power density. This does not apply to Dual Fluid and the entire spectrum of modern industrial materials can be used, the company says, noting that even noble metals can be used as components of the alloys with little impact on the overall cost of the system. Examples of such materials are the alloys of refractory


metals or highly corrosion resistant ceramics such as silicon, titanium or zirconium carbide, which have been increasingly used in industry in recent decades for applications under extreme conditions. In addition, coatings with substances such as yttrium oxide, which is resistant to pure uranium up to 1500°C, are also possible. Since the temperatures in the reactor core are significantly lower than this, and moreover the fuel does not consist of pure uranium but of a uranium-chromium mixture, the identification of the most suitable materials represents a “solvable development task”, says Dual Fluid.


Safety features The most important safety feature of the Dual Fluid design is the reactor´s instantaneous self-regulation, made possible by the very negative temperature coefficient. If the temperature increases, the nuclear fuel expands. As a result, the reactivity immediately subsides and the temperature drops. The reactor is thus completely self-regulating; a power excursion such as that which occurred at Chernobyl is ruled out.


If the system nevertheless heats up beyond the normal


operating temperature – “conceivable only due to incorrect fuel composition” – melting fuse plugs provide additional protection.


The fuse plug (shown in Figure 5) is an actively cooled section of the fuel line near the lowest point. The fuel is actively cooled there from the outside, so that it freezes locally and closes the downstream outlet. If the fuel overheats, the frozen fuel plug melts and the liquid drains downward under gravity into subcritical tanks. The chain reaction stops immediately and the decay heat is removed purely passively, ruling out accidents where decay heat is not removed (eg, Fukushima). This simple control system concept cannot be compromised and has already proven its worth in the US molten salt reactor experiment of the 1960s, Dual Fluid observes. For effective protection against violent impact and


earthquakes, the nuclear part of the plant would be located underground in a thick-walled bunker. Even in the worst possible accident scenario – a leak associated with the fuel circuit – no radioactive material would escape to the outside, since there is no significant pressure and nothing could explode.


Route to serial production Following around 10 years of groundwork, conducted principally at the Institute for Solid-State Nuclear Physics in Berlin, the Dual Fluid technology is estimated to be at TRL3. The next step towards commercial deployment is component testing, as shown in Figure 6. Academic partners are pursuing analyses of the stability


of the system as a basis for licensing and the seed funding round was successfully completed in June 2021. If everything goes to plan, the hope is to produce a working prototype within a decade and start series production soon thereafter. ■


This article was first published in NEi sister title Modern Power Systems. Further reading: Reinventing nuclear, by Dual Fluid: (https://dual-fluid.com/wp-content/uploads/2022/03/ Dual-Fluid-Whitepaper.pdf)


www.neimagazine.com | July 2022 | 39


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