AGOT graphite

The pebble zone is a volume 7 ft 4 in. square by 9 ft high surrounding the reactor tank and filled by some 7T)0,000 l-in.-diameter AGOT graphite pebbles. The pebbles rest on a base plate.mounted on the lower thermal shield plate and are free to expand upward. In this way any expansion due to radiation effects or temperature increase will merely raise the level of the balls without exerting undue stress on the tank wall or the permanent graphite. 

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