Safe, Factory Mass Producible Truck Sized Nuclear Reactors

A new Very-Small, Long-LIfe, and Modular (VSLLIM) reactor design has been developed at the University of New Mexico’s Institute for Space and Nuclear Power Studies. It offers passive operation and decay heat removal and redundant control to make it walk-away safe. During nominal operation and after shutdown, the VSLLIM reactor is cooled by natural circulation of in-vessel liquid sodium (Na), that is enabled using in-vessel chimney (1–2 m tall) and helically coiled tubes Na-Na heat exchanger, placed at the top of the downcomer. The reactor can generate 1.0–10 MWth, depending on the height of the chimney and the HEX design, at an average fission power density up to 23.47 MWth/m3. The VSLLIM reactor can potentially operate continuously, without refueling for ∼92 and 5.9 full power years (FPY), respectively, and slightly below atmospheric pressure, owing to the sodium low vapor pressure. The core is loaded with hexagonal assemblies of fuel rods with UN enriched to 13.76%, and has independent systems for emergency shutdown and nominal control.

Highlights of the SLIMM Design

* Walk away passively safe
* smaller than a shipping container
* factory mass-producible
* Narrow and small design could fit on rockets for space applications

As many as 10–30 units could be deployed incrementally at a single site, commensurate with the increase in electricity demand, for a plant total electricity generation of up to 120 MWe. These VSLLIM power plant modules could also be integrated into either a distributed or a central grid, with renewable energy sources, or operated alone. They can also provide both electricity and process heat for industrial uses and district heating.

It also has two independent systems for safe passive removal of decay heat after shutdown, and following an unlikely malfunction of in-vessel HEX. These are liquid metal heat pipes (LMHPs) embedded in the primary vessel wall, and natural circulation of ambient air along the outer surface of the guard vessel wall. The LMHPs are thermally coupled to thermoelectric elements for generating 10 s of kW of auxiliary DC power, independent of on-site and off-site sources, both during nominal reactor operation and after shutdown. The sodium coolant enters the fast-neutron energy spectrum core at 610 K and exits at ≤755 K, depending on the reactor thermal power. At these temperatures, Na is compatible with the HT-9 Ferritic-Martensitic steel cladding, core structure and reactor vessel.

The reactor would be fabricated, assembled and sealed at the factory, and transported by rail, truck or barge to a permanent site and installed underground, to protect against an airplane or a missile impact, and mounted on seismic isolation bearings, to resist earthquakes. At the site, the VSLLIM module could use a superheated steam Rankine cycle or a supercritical CO2 Brayton cycle for electricity generation at high thermal efficiency. Alternatively, a VSLLIM power module, with an open-air Brayton cycle, could be deployed on a portable platform or a truck, to provide both electricity and/or process heat at remote sites, hospitals, data centers, natural disaster areas, arid or desert regions, and advanced military bases.

Annals of Nuclear Energy
Volume 129, July 2019, Pages 181-198 – A walk-away safe, Very-Small, Long-LIfe, Modular (VSLLIM) reactor for portable and stationary power

37 thoughts on “Safe, Factory Mass Producible Truck Sized Nuclear Reactors”

  1. The diagram clearly shows the decay heat removal system being an air siphon directly in contact with the vessel wall. Although these things are tested at the lab scale as part of the design process, I think it’s reasonable to say they would test this system, assuming it had licensable metallurgical margin… meaning the test didn’t ruin the system as would happen in a LWR design basis depressurization. They did isolate EBR2 in a test like this; it had a different, but similar DHR system.

  2. The article did say so. Do a find on redundant. Better to be safe by physics than to be safe by complex hardware and software. Does any one actually test a reactor and its safety system to failure. If you don’t how do you know the safety system actually works.

  3. It may not be fast, but regular props driven by electric motors should work just fine. Usually, the big planes don’t move that fast anyway. 480mph is doable with props. The C-5M Super Galaxy normally cruises at 518mph. 40mph slower is not a huge concession in speed.

  4. A more realistic figure might be $250-350 million. It is hard to guess how much they can save with economies of scale and how automated they can make production. The first ones won’t be cheap though.
    You have to consider that with that money they could have 2 ships earning money. And borrowing money is not free either.
    Though, by spending a bit more on the ship, it might be able to last 50 years instead of 25 (perhaps more stainless steel). Though you run the risk of the design becoming obsolete in some way. Perhaps ships 25 years from now will be 5 times the size and require half the crew. Or maybe you will have trouble finding crew because personal quarters are larger on future ships or even allow them to take their families along.
    Electric motors can increase the damage, if a ship takes on water in a storm or accident. Salt water will ruin an electric motor. People may also be reluctant to help you in an accident if they know your ship is nuclear. You are also a fat target in the Middle East and cargo ships go through the Suez carnal very often. It is also quite a prize for pirates. Regulations could also force you to have more crew than you otherwise would have…or even prevent you from stopping at some ports. New Zealand won’t allow it. That list could grow.
    Aluminum sails augmenting? That should pose few issues.

  5. I want to know if these are ship safe. The sooner we can start replacing those bunker oil burning container ships the better.

  6. Nuclear doesn’t have to take that long. The Nautilus was under way on nuclear power about a decade after a uranium chain reaction was first demonstrated, and power reactors were installed in Antarctica, and under the ice in Greenland, within a couple of years of being ordered. With the timelines between concept and finished plant that today’s engineers have to put up with, it’s small wonder if only grumpy old s.o.b.s like Scary are left in the industry.

  7. The British CO2 cooled reactors had a very big pressurised containment in relation to their power output, since a gas is not nearly as good a heat carrier as liquids like water, molten salt, or molten metal. The large containment made them expensive to build, which is probably the main reason why nobody followed the Brits down this path. ( The French had a version, and a few others were built, but they were short-lived.) In theory, sodium cooled reactors should be cheaper to build than water-cooled, since they’re low pressure, compact, don’t have to worry about zirconium-water reactions, and volatile radionuclides like iodine or cesium are more likely to bind to the sodium than gas out in an accident. Sodium is reactive, but the reaction is low energy compared to hydrogen, and can be managed. Nobody has ever been killed by a reactor sodium fire, whereas methane explosions kill dozens every year.
    On the other hand, in the last year the French and Japanese sodium fast reactor programmes have been cancelled, the Russian commercial version has been deferred for a decade, and the Indian prototype has been delayed yet again.

  8. The big girls are large enough that they could be nuclear powered themselves. Then you could have a nuclear reactor delivered by a nuclear reactor powered truck.

  9. While “very efficient” sounds nice….it ignores just how much fuel these ships use. The OOCL G class shipping vessel uses 21,200 gallons per day. This is one of the largest vessels out there for cargo, and is incredibly efficient compared to may other vessels. Or about 42,000 dollars a day in fuel costs. Plus these vessels would free up a ton of space that could be used for cargo instead of fuel. 1,428 sailing days would make this a break even proposition if we used your 60 million dollar estimate. The vessels have a life expectancy of about 25 years say.

    This is a VERY attractive proposition. Plus electric powered motors are FAR more reliable.

  10. Truck sized implies “fits in a SpaceX’s BFR/Starship”.

    That can be a critical requirement for some applications.

  11. Ships are very efficient. It would be a challenge to make that economical. Not saying it is impossible to make a cheap well designed compact reactor…but no one has come close. They are only paying about $120 m for a large tanker. That reactor setup will probably add at least 50% to that cost. And I think that price is almost absurdly optimistic.
    There was a rigid sail cargo vessel experiment. Worked fine. Still, they couldn’t wait to get those things removed. Modern aluminum wing sails could easily power the ships for much less expense than a reactor. There is renewed interest, but mostly by environmentalists and engineers, the actual shipping companies don’t give a crap.
    Nuclear in ships is mostly about speed. In subs it is additionally about not needing oxygen.
    If people still wanted to take luxury ships across the ocean like the Queen Marry, it might make sense there. But people don’t, even if it could do 70mph.
    Well, I am just guessing there. I could be wrong. Maybe people would pay for 70mph across an ocean. It would still be reasonably quick across the ocean and be much more pleasant than a cramped airplane. That would take just 2 days from N.Y. to London. If you have a 2 week vacation, just 4 days would be on the ship, and if your holiday is very busy seeing the sights or whatever, a 2 day cruise to wind down after doesn’t sound that bad.

  12. Simply allowing the reactor to be built to a pre-approved design would reduce the risk of budget overruns, too.

  13. Big planes. C-5M Super Galaxy can lift over 280,000 lb. And the motors will weigh much less than jet engines. I think the real question is how much do we need the reactor to put out.
    Also you have to consider that the jet currently has to take on a large load of jet fuel.

    And I am not saying we have to use it as a cargo plane. It can have intelligence stuff. Or move bulky but less heavy stuff.

  14. Such designs have been made before. Their common difficulty is investment and commitment: apparently no one wants to pay for permits, demo units, capital assets, etc. People today also tend to want things now, and nuclear always takes time: faced with a notional 10 years waiting time, people tend to walk away or prioritise other toys that are available now. Shame, really, but that is an obstacle that nuclear work of any type is facing today. Any nuclear power project is at the time scale of human life: 50~100 years, from start of construction to end of decommissioning. People today usually cannot fit that in their minds: a 50 year project? oh, a 100 year project? I am 40, 50, 60 — why would I bother?

  15. What this means is you need a lot of extra reinforcing to stop the reactor tearing out through the lightweight aeroplane structure the first time it hits turbulence.

    Apparently this is a real issue for piston engined planes. The piston engine is much heavier and denser than any other part of the plane, and during super bad turbulence or way-beyond-design-spec aerobatic maneuvers, you might find that your engines have continued moving in a straight line in accordance with Newton’s laws of motion. Despite the rest of the plane not doing so.

    A reactor makes an aluminium block piston engine look like aerogel.

  16. Yes, but helium isn’t affordable at 500C either as it isn’t efficient enough at that temperature.

    Sodium cooled reactors really aren’t viable unless you don’t care about cost.

  17. Sorry, I love the tech, but sodium, upon exposure to air, burns, and upon exposure to water, explodes. I remember the ancient UK Magnox reactors, which were moderated and cooled using regular CO2. Now, a mini-reactor for this would be enormously safer compared to sodium, and water reactors, which a nuke pile converts water to steam, and then steam to hydrogen, and then, kaboom! My guess is that we are heading into a world powered by wind, solar, and then nat gas turbines. No, I am not a Green-Red. The tech is so much easier, and cheaper. Do really care where your electricity comes from? As long as it flows, nobody knows.

  18. Airplanes might be a lunacy but having nuclear-powered supertankers would be feasible even with non-proliferation concerns

  19. The biggest issue with nuclear energy is that with the current approach it is too expensive and too risky to build with delays and budget overruns. Smaller reactors reduce the risks of budget overruns, and hopefully the [overnight] costs.

  20. They don’t say it NEEDS redundant controls to be safe.
    And safe doesn’t mean ideal. You can be walk away safe while still preferring to remain under control.

  21. If that number is correct, 20 mton is far less than the weight of Kerosene on large planes of which there are double digit thousands. Examples: model A300B4-200[84] Fuel capacity 48,470 kg (106,858 lb) // A300-600R[85] Fuel capacity 53,505 kg (117,958 lb) A300-600F[86] // Fuel capacity 48,470 kg (106,858 lb) 53,505 kg (117,958 lb).
    Nevertheless, putting a reactor on a plane would never be a good idea. It is quite predictable that they will get shot down, hijacked on purpose and this with non-trivial consequences.

  22. It ain’t really walk-away safe if it needs redundant control to make it walk-away safe. Just saying. And if you need 30 small reactors to equal one big reactor then each smaller reactor better be more than 30 times as safe.

  23. You made me laugh out loud.

    They modify roads specifically just to deliver wind turbine parts to projects and it doesn’t break the bank, it stands to reason they’d do the same for Nuclear SMRs. The truck/container size target is just so silly to me….

  24. It is also a big advantage for reducing capital cost in general. 50% efficiency vs 33% or so for a PWR and 30% for a BWR so you cut overall costs by 1/3.

    Although sodium reacts with carbon dioxide at high temperatures so from a safety perspective it very much complicates things; I doubt a sodium reactor can affordably be paired with supercritical CO2.

  25. If we distribute the same amount of radioactive fuel among more number of reactors, than in case of one of them failing it will cause less fallout. Maybe, that was a point. Anyway SSR-W300 is safer, I would bet.

  26. quick hand calc of 1.5m right cylinder of uranium nitride with 25% void for cladding and cooling channels comes in at over 20 tons. Not for airplanes.

  27. Next time i’m asked about my temperature I am going to reply in Kelvin.

    At least it is truck sized (as we all know, a critical requirement).

  28. This potentially could power an aircraft for months or years at a time. Of course, the weight could go up pretty quickly trying to protect this from making a mess if it crashed or was shot down.

  29. Using a supercritical CO2 Brayton cycle would allow these reactors to be sited away from large bodies of water. Heat could be rejected at a high enough temperature so that dry cooling towers, greenhouses, or hydronic based central heating districts are options.

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