The Cryogenic Containment Unit was used to contain Akira after he destroyed Tokyo. It is located among the ruins of Old Tokyo.
The containment unit is made up of many layers, with a liquid helium coolant being pumped between them. The center layer, in which Akira is stored, is kept at a temperature of 0.0005 K (-273.149 °C, -459.6691 °F.)
Anime
After the destruction of Tokyo, Akira was dissected and studied until there was nearly nothing left of him. The containment unit was used to store all samples and other remains in order for them to be studied by scientists in the future.
The containment unit is destroyed by Tetsuo in his hopes to find Akira still living.
Manga
The containment unit was used to store Akira. He was placed here, still living, in order to prevent any further destruction. Akira was freed from stasis by Tetsuo.
The containment unit was later used by Tetsuo to store Kaori, after she died.