Seaborg's solution is to use another molten salt – sodium hydroxide – as a liquid moderator. Thus, the core design places the fuel salt tube inside a larger tube filled with sodium hydroxide, creating a first-of-its-kind all-liquid reactor that's remarkably compact. But sodium hydroxide itself is a powerfully caustic base, often used as oven cleaner or drain cleaner; the Seaborg design has to deal with this added corrosive agent too.
And on top of all that, there's the freaky phenomenon of "grain-boundary corrosion" to boot, caused by the presence of tellurium as a fission by-product in the fuel salt stream. Tellurium atoms can merrily penetrate through metals, and swap positions with other elements, leading to embrittlement of the metals at their weakest points.
The company is well aware of its key challenges here. "Seaborg’s core IP is based on corrosion control in the moderator salt, and applying the lessons learned since the 1950s," says Pettersen. "But it is not just a question of corrosion, it is also how easy it is to put these things together. Hands-on experience is important. They need to be welded, tested, inspected, maintained. We are working towards having perhaps 20 or 30 test loops in Copenhagen, with the experiments designed, set up and executed. The conceptual design is already done; we are now working on the basic design and in that way we are working up towards a full-scale prototype."
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