NANO DEEP DIVE | SPECIAL REPORT
Having effectively established a business framework this in turn informed substantive design elements: “Once we had that business model in mind, we knew that we had to get the micro-reactors to be very portable, they had to be passively cooled so they’re extra safe, they had to have very few mechanical parts, wouldn’t need many personnel, and they had to be able to move by road, ship, or train, so you could deploy it anywhere very easily.
Reactor design fundamentals Given the constraints imposed by the business model the two technical teams were given the same guidelines as the starting point for their designs but both teams came up with novel solutions. For the ZEUS team out of University of Berkeley – ZEUS is the name of their reactor – their solution was to remove the coolant completely and to instead have a solid core. In this case thermal conduction is harnessed to remove the heat from the uranium to the periphery of the core, and then normal air circulation takes that heat from the periphery of the core for use. “That’s pretty much as simple as you could make a reactor,” says Walker, adding: “We even call it a nuclear battery, because I don’t think you can simplify it any more than that.” Meanwhile the ODIN team out of the University of
Cambridge came up with a different approach. “They thought a lot more about deploying a more commercial product, and so they wanted to use more technology readiness level technology with off-the-shelf components, known fuels, and known technology so the licensing would be very easy.”
Their solution was a solar salt utilizing thermal
convection, while using natural circulation to remove the heat. “Again, it’s incredibly basic, and the benefit of ODIN actually is it operates at a lower temperature with less thermal stresses, and it’s cheap to manufacture,” notes Walker. For both reactors, because the power output is relatively
small, there is still a large volume of space within the iso-container dimensions, which was the primary size constraint, which allows peripheral systems like the turbine to be included within the standard containerised unit. Both machines operate a Brayton cycle turbine which supports a compact design. “Operating a water-cooled reactor at above 100° means it needs to be highly pressurised and that leads to a more complicated safety case and longer licensing period. If you use solar salt as with ODIN you avoid those issues because the boiling point of the salt is obviously much higher. If you can remove the pressuriser, the reactor shrinks down further and on the ZEUS reactor, their solution
was to remove the coolant completely,” he says. Walker also notes that the University of Cambridge is deeply involved with aircraft carrier turbines allowing NANO to develop its own optimized turbine to suit both reactor designs that will be installed with them. While the reactors are quite different in their design philosophy, Walker is confident this is the right approach: “We can envisage a situation now where, even though we built two reactor teams to de-risk our endeavour and so we would have two modes of success, the reactors ended up being quite complementary, because ODIN is cheap to manufacture, can be mass manufactured very easily and deployed, whereas ZEUS has a higher operating temperature and can be more useful for things like process heat for industry. We’re still pursuing both for that reason,” he says. Furthermore, the two teams offer other advantages, as
Walker explains: “The technical teams actually can feed off each other and act as a sanity check to come in and audit each other as we go along. The knowledge that one team has they can actually pass on if it’s something like heat exchanger work that both teams can really benefit from. Sometimes we combine the work even if there have been big benefits of doing two different designs.” A key part of the design approach has been aimed
towards regulatory approval and licensing and NANO has taken substantial measures to engage with regulators from the outset. “We’ll always be looking to refine and develop and improve upon what we’ve got but I still think in the micro-reactor space, as far as launching a commercial product goes, we’re really in the lead because we’ve anticipated the regulatory requirements and how to actually design around those and we’re very transparent too. I think we’re the only micro-reactor company that paid the government to put an engineering team on our reactor and tear it apart, look at it and give us feedback,” says Walker. According to Walker, both reactor designs were subject
to an in-depth audit by Idaho National Laboratories, principally for that reason. “That external validation and input is actually very useful,” he says, noting that the output from those engineering investigations builds into the licensing documentation. The University of Cambridge team that have been working on the ODIN reactor have a higher technology readiness level and have now completed the design and all the related computer modelling and concept work. Now they moving into the construction of test rigs that will be used for model validation, but also provides the data needed for the licensing process. “The Cambridge team
www.neimagazine.com | July 2024 | 39
Above left: The ODIN reactor design from the NANO Nuclear team
Above right: The NANO Nuclear Energy ZEUS reactor
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