The probability of collision with a ship of this remaining 1 percent
group is extremely low. Considering that the SAVANNAH, as the first
nuclear-powered merchant ship, will be handled with extreme care, the
probability of a dangerous release of radioactivity through collision is
negligible. Because large ships proceed at relatively low speeds in
harbors, and because of the built-in invulnerability of the SAVANNAH,
the probability of a collision of sufficient severity to damage the
reactor compartment is extremely low.
Surrounding the reactor compartment are heavier-than-normal structural
members. The inner-bottom, below the reactor space, is “egg crated” with
transverse floors at every frame; and a deep vertical keel with more
than the usual number of keelsons in the fore and aft direction add to
this strengthening. Outboard of the reactor compartment are two heavy
longitudinal collision bulkheads; outboard of these bulkheads there is
heavier-than-normal plating continuously welded to the beams. Inboard of
the collision bulkheads are collision mats made up of alternate layers
of 1-inch steel and 3-inch redwood planks for a total thickness of 24
inches.
In the event of a collision broadside to the reactor compartment, the
ramming ship would have to penetrate 17 feet of stiffened ship
structure, the collision mat, and the reactor containment vessel, before
reaching the reactor plant.