Patent Number: 052689441
Section: claims

1. In a nuclear reactor having a primary shield and a generally cylindrical reactor vessel having a generally hemispherical lower end, said reactor vessel being disposed within an opening in said primary shield, said opening being defined by an inner surface, said reactor vessel being supported within said opening in said primary shield by a plurality of angularly spaced reactor vessel supports connected to said primary shield and on which said reactor vessel is supported, and reactor vessel thermal insulation disposed between said reactor vessel and said primary shield and surrounding a lower portion of said reactor vessel, wherein the improvement comprises: said inner surface of said opening in said primary shield includes a plurality of generally planar side walls which form a polyhedral-shaped opening into which said reactor vessel is disposed; and  said thermal insulation includes a plurality of slidably insertable and removable generally planar panels forming an insulation polyhedron surrounding at least said lower portion of said reactor vessel.  said insulation polyhedron has a shape which substantially corresponds to the polyhedral shape of said opening in said primary shield.  said polyhedral-shaped opening in said primary shield has a plurality of corners between said generally planar side walls; and  excore detectors are mounted in at least some of said corners such that said insulation is not disposed between said excore detectors and said reactor vessel.  each said side wall has a central portion adjacent to said reactor vessel;  said vessel supports are in communication with at least some of said side walls; and  each said reactor vessel support has a central portion which is aligned with and at least partially supported by said central portion of one said side wall and said reactor vessel engages and is supported by at least said central portion of each said reactor vessel support.  said generally planar panels include a plurality of generally rectangular side panels oriented generally longitudinally with and surrounding said generally cylindrical portion of said reactor vessel, said side panels being disposed generally parallel to said side walls of said primary shield, a generally planar central panel disposed below a central portion of said hemispherical portion of said reactor vessel and oriented generally perpendicular to said side panels, said central panel having a plurality of generally linear edges oriented generally parallel to said side walls, and a plurality of generally planar, generally trapezoidal-shaped connecting panels connecting lower edges of said side panels to said edges of said central panel to form said insulation polyhedron.  said opening in said primary shield includes eight said side walls which form a polyhedral-shaped opening having generally octagonal cross-sectional shape; and  said insulation polyhedral includes eight said side panels forming a polyhedron having a generally octagonal cross-sectional shape.  providing said primary shield having a generally polyhedral-shaped opening therein defined by a plurality of generally planar side walls;  supporting said nuclear vessel said opening in said primary shield with the reactor vessel supports;  surrounding at least a lower portion of said reactor vessel with a plurality of generally planar insulation panels such that said panels form an insulation polyhedron substantially enclosing said lower portion of said reactor vessel; and  mounting said panels for sliding into and out of position around said vessel.  surrounding said generally cylindrical portion of said reactor vessel with a plurality of generally rectangular side panels of insulation, providing a generally planar central insulation panel below said hemispherical end of said reactor vessel and oriented generally perpendicular to said side panels, and connecting said side panels to said central panel with a plurality of generally trapezoidal-shaped connecting panels of insulation to form said insulation polyhedron.  providing eight said generally planar side walls to define a generally polyhedral-shaped opening having a generally octagonal cross-section; and  providing at least eight said side panels of insulation to form an insulation polyhedron having a generally octagonal cross-section. 2. The nuclear reactor of claim 1, wherein 3. The nuclear reactor of claim 2, wherein 4. The nuclear reactor of claim 3, wherein 5. The nuclear reactor of claim 4, wherein 6. The nuclear reactor of claim 5, wherein at least one of said generally planar panels is mounted on at least one of said excore detectors. 7. The nuclear reactor of claim 5, wherein 8. A method of thermally insulating a lower portion of a generally cylindrical reactor vessel of a nuclear reactor, said nuclear reactor further having a primary shield and reactor vessel supports, said reactor vessel further having a generally hemispherical lower end and being disposed within an opening in said primary shield, so as to provide space between said primary shield and said reactor vessel, comprising the steps of: 9. The method of claim 8, further including 10. The method of claim 9, further including