The Calandria Vault Top Hatch Cover Beams and Deck Plate Assembly consist of west beam, central beam and east beam.
When placed on the top of the Calandria Vault (CV), these parts form the roof of the CV. Nuclear radiation, mainly gamma radiation from the CV above the calandria are attenuated by these beams and deck plates, thus reducing gamma dose rate to acceptable limits.
The Central Beam houses sleeves through which various reactivity devices/rods pass into the calandria. On the top plate of the central beam, two fabricated I-section carbon steel beams, 53 cylindrical sleeves at AR/CR/SR/VP locations, and auxiliary support sleeves are welded.