Nuclear reactor having a polyhedral primary shield and removable vessel insulation

A nuclear reactor is provided having a generally cylindrical reactor vessel disposed within an opening in a primary shield. The opening in the primary shield is defined by a plurality of generally planar side walls forming a generally polyhedral-shaped opening within which the reactor vessel is supported by reactor vessel supports aligned with central portions of some of the side walls. A thermal insulation polyhedron formed from a plurality of generally planar insulation panels substantially surrounds at least a portion of the reactor vessel and is disposed between the reactor vessel and the side walls of the primary shield. Reactor monitoring instrumentation may be mounted in the corners of the opening in the primary shield. (Author)