This is great news. The Xe-100 reactor design is not that different from the Kairos Hermes reactor that was yesterday in the news [1]. They both use TRISO pebbl

This is great news. The Xe-100 reactor design is not that different from the Kairos Hermes reactor that was yesterday in the news [1]. They both use TRISO pebbles, they are both slow (or thermal) reactors, and they are both SMR's that produce very nearly the same output (80 MW for Xe-100, 75 MW for Hermes). The only difference is the coolant: it is helium for this reactor, and FLiBe molten salt (a mix of lithium and beryllium fluorides). Helium is a gas, so it's much less dense than a molten salt, which is a liquid. Surprisingly, helium has a very high specific heat (5.2 J/gK), higher even than the specific heat of water (4.2 J/gK). FLiBe has about 2.4 J/gK specific heat. Helium can travel through the core at a much higher speed, so overall, the disadvantage of being a gas is not that great. The Hermes reactor is projected to have about twice the power density of the Xe-100 reactor. There are some great things about Helium though. One is that Helium-4 (which represents 99.9998%) is the only isotope in the universe that has exactly zero neutron absorption cross-section. All other coolants absorb some of the neutrons in a reactor, but helium doesn't. It is also an inert gas, so it does not pose the various corrosion problems posed by other coolants and moderators (like water for NuScale, FLiBe for Kairos, sodium for Natrium, lead for Westinghouse). China did already put in production two reactors of the same type as Xe-100, the HTR-PMs. They appear to be working just fine. Good luck to X-Energy. [1] https://news.ycombinator.com/item?id=41840769 https://news.ycombinator.com/item?id=41840769