Vault 76

Vault 76 is one of the Vault-Tec vaults shown on the computer in the Citadel. The Vault-Tec Terminal in the Citadel lists Vault 76 as a "control" vault, with 500 occupants. The vault was designed to open after 20 years. It was among the seventeen total control vaults, meaning it functioned precisely according to occupants' expectations.

Appearances
Despite being mentioned in Fallout 3, Vault 76 does appear in the game. Its located in the top right section of the map. A couple of meters away from the Alien crash site.