Some years ago it looked like the future of small reactors might be so-called pebble bed modular reactors (PBMR). I wonder what ever happened to them. IIRC the

Some years ago it looked like the future of small reactors might be so-called pebble bed modular reactors (PBMR). I wonder what ever happened to them. IIRC the most salient outstanding issue seemed to be that there way no clear way to handle a graphite fire.