Total world Be resource is estimated to be 100,000 tons, although that's likely an underestimate. Still, the MSRE (a 7.4MW(th) reactor) used about a ton of beryllium in the fuel and secondary coolant salts. The world would need several million times the thermal power output of the MSRE to replace fossil fuels.

The ARC fusion reactor concept would require even more Be per MW(th) of output.