Looking at the link, it looks like it poses its own challenges: >The most common criticism of pebble-bed reactors is that encasing the fuel in combustible grap

Looking at the link, it looks like it poses its own challenges: >The most common criticism of pebble-bed reactors is that encasing the fuel in combustible graphite poses a hazard. When the graphite burns, fuel material could be carried away in smoke from the fire. These sound like solvable engineering and process challenges, though, so perhaps in the less anti-nuclear climate we’ll have the will to actually make it work.