The double containment concept developed for Madras Atomic Power Project was taken further in the nuclear reactors at Narora. This was achieved by restricting the inner prestressed concrete container to the radioactive source of energy. The other source of energy i.e. the steam generators were placed outside in the RCC containment. The slab separating the high pressure space (when there is a Maximum Credible Nuclear Accident) was designed as a cellular grid. Independent safety valves in the outer containment called blow out panels, for boiler related accidents, eliminate high pressure rise in the second containment. Further, the annular space between the containments and the voids in the slab are permanently maintained at a negative pressure in order to minimize the danger of radioactive gases leaking into the atmosphere. Instead of a single protective layer above the radio-active source, this design has a dedicated double containment.

The entire structural design concept for double containments, including air lock barrels, was developed by Assystem Stup. The concept was developed further into design engineering and detailing, and supervision was provided until completion / testing of containment structures.