Seems like the pebbles are much smaller in these. I recall one very mundane but difficult issue with previous pebble bed reactors was pebbles jamming and other mechanical problems with the fuel. These seem like they'd flow like that weird pseudo-sand stuff in kids toys.

These very small fuel particles are embedded in larger graphite structures with whatever geometry is convenient for handling. (Pebble bed pebbles are one such possibility, and PBRs have been made which use TRISO-based fuel pebbles.)