The primary shield, immediately surrounding the reactor pressure vessel,
consists of a 17-foot-high lead-covered steel tank that surrounds the
reactor vessel with a 33-inch water-filled annulus. The tank extends
from a point well below the active core area to a point well above it.
The active core height within the reactor is only 60 inches. Constructed
of carbon steel, the primary shield tank is covered with a layer of lead
varying in thickness from 2 to 4 inches. When the tank is filled with
water, the dose rate outside the primary shielding from core gamma
sources and activated nuclei will not exceed 200 mr per hour 30 minutes
after shutdown. This is sufficiently low to permit entry into the
containment vessel for inspection or maintenance.