The beryllium is surrounded by a water reflector of effectively infinite thickness. In the axial direction, the reactor is reflected by water. The control plates, in the form of two thin, poison-bearing concentric cylinders, are located in an annular region between the outer fuel element and the beryllium reflector. These plates are driven in opposite directions. The outer control cylinder consists of four separate quadrants, each having an independent drive and safety release mechanism.
Reactivity is increased as the outer plates are raised.
Any single rod or cylinder is capable of shutting the reactor down. The reactor instrumentation and control system design reflects the emphasis placed on the importance of continuity of operation while maintaining safe operation. Three independent safety channels are arranged in a coincidence system that requires agreement of two of the three for safety shutdowns. Additionally, three independent automatic control channels are arrayed so that failure of a single channel will not significantly disturb operation. The primary coolant enters the pressure vessel through two 16-in.