Not OP but he maybe referring to the new gas cooled gen 4 reactors not Soviet RBMKs. The ones I heard are working with sealed beads of uranium, encased in porous carbon, then some other layers, including some carbide (silicon?). The porosity of carbon absorbs gases but they ultimately stay sealed. The whole thing is helium cooled.
Yeah. I was listening to David Ruzic's video [1] about them getting one of those reactors on campus and when he showed the structure of beads, that's the first thing that popped in my head - at that size how are they going to ensure every single bead has an intact surface.
