Graphite sleeves are the hollow cylindrical envelopes made from graphite that surrounded the fuel elements in the first French nuclear power plants. Production of these sleeves stopped in 1994. The fuel element was removed from the sleeve when the fuel was unloaded from the reactor. The wire locks, which were the stainless steel wires used to hold the fuel element in place, are the source of significant cobalt-60 activity. Some 360,000 sleeves, mostly with their wire locks, are stored in two partially buried silos owned by AREVA.