The primary function of the containment shell is to surround the primary
system and provide complete containment of any radioactive matter that
might escape from the system. The design pressure of the vessel was
determined by postulating the instantaneous release and expansion of the
entire contents of the primary system. This approach is highly
conservative because of the improbability of a large rupture.
A study has been made concerning the penetration of the vessel wall by a
piece of debris in an explosion. An analysis of the penetrating power of
high-speed components indicated that the shell would contain the largest
missile that could be expected.
The shell is cylindrical in shape, 35 feet in diameter by 50.5 feet
long, and is centrally located on the ship’s bottom.
The containment shell is sealed at all times during plant operation.
Entry to the shell will be made only after the reactor has been shut
down, the shell purged with air, and the radiation level has dropped
below 200 mr per hour.
The bottom half of the shell rests in a cradle of steel surrounded by a
48-inch-thick wall of reinforced concrete.
The top half of the containment shell is covered by a 6-inch layer of
lead plus a 6-inch layer of polyethylene. During normal power operation,
this reduces the radiation level to less than 0.6 mr per hour at the
nearest point of access by the crew.