NS Savannah - Containment
A large containment vessel housed the majority of the equipment associated with the nuclear reactor. This vessel was designed to contain all the water and steam released in the event of a failure of the pressurized water loops. The vessel is made up of a 35' diameter cylindrical section, with hemispherical ends. It has an overall length of 50'. The wall thickness, varying from about 2.5" to almost 4" of carbon steel, was designed to withstand a pressure of 186 psig. The 186 psig. is the pressure that would result from the rupture of a primary coolant pipe and the instantaneous release and expansion of the contents of the primary system.
A total of 82 penetrations for piping, electrical cables, pneumatic lines, and access, are provided in the containment shell. The largest penetration is the 14'-diameter "cupola" at the top. This opening was used for initial installation of equipment within the containment vessel, as well as for refueling the reactor core. Two 24" x 18" manholes in the lower portion of the vessel and two 42"-diameter manholes in the upper portion provide access to the containment vessel. If the ship sank, the two lower manholes were designed to open inwardly under an external head pressure of 100' of water. This allowed flooding and prevented the collapse of the containment vessel. Except when entry was necessary, the containment vessel remained sealed. If entry was required, it could be done thirty minutes after the reactor was shut down, once the radiation level within the vessel was below 200 millirem per hour. Entry into the containment vessel was minimized since the internal equipment requiring normal maintenance was installed in duplicate. In addition, certain segments of the reactor system could be isolated and bypassed without affecting plant operation.
The bottom half of the containment vessel rests in a cradle of steel surrounded by a wall of reinforced concrete 4' thick. The top half of the containment vessel is encased in a 6" layer of lead, plus a 6" layer of polyethylene. In addition, both sides of the containment vessel are protected by a 24" thick collision mat constructed of alternate layers of 1" steel and 3" redwood lumber.
According to design estimates, in the event of a broadside collision opposite the reactor space, the ramming ship would have to penetrate 17' of stiffened ship structure, the heavy collision bulkhead, 2' of collision mat, 1.5' of reinforced concrete shielding, and the reactor containment vessel, before the reactor plant could be damaged. The high strength of the inner-bottom, plus the very strong supports for the containment vessel, also offered strong resistance to reactor plant damage due to grounding.
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