How are the radioactive pebbles disposed of from pebble bed reactors?

Answer 1

The fuel in the pebble bed reactor (PBR) is permanently contained in the pebbles, and this will apply after discharge. Hence disposal of the spent fuel also implies disposal of the graphite and other material in the pebbles. It is not likely that any attempt to process the pebbles would be made. They would be stored in shielded repositories, on the station site at first and then in a geologically safe place for long term storage. This would be dry storage but some arrangement would be required to remove the decay heat. Since an array of pebbles is all that is needed for a critical assembly, consideration would have to be given to the geometry of storage, unless it can be shown that the depleted used fuel is always safe.

(Following part from Wikipedia)

Since the fuel is contained in graphite pebbles, the volume of radioactive waste is much greater, but contains about the same radioactivity when measured in becquerels per kilowatt-hour. The waste tends to be less hazardous and simpler to handle. Current US legislation requires all waste to be safely contained, therefore pebble bed reactors would increase existing storage problems. Defects in the production of pebbles may also cause problems. The radioactive waste must either be safely stored for many human generations, typically in a deep geological repository, reprocessed, transmuted in a different type of reactor, or disposed of by some other alternative method yet to be devised. The graphite pebbles are more difficult to reprocess due to their construction, which is not true of the fuel from other types of reactors. Proponents point out that this is a plus, as it is difficult to re-use pebble bed reactor waste for nuclear weapons.