Patent Number: 047160128
Section: claims

1. In combination, an upright cylindrical nuclear reactor pressure vessel having a hemispherical lower head section with a curved inner surface and defining an annular flange extending radially inward near its upper end, reactor internals suspended within said pressure vessel from said flange, said internals extending downward into said hemispherical lower head section but with the lower end thereof terminating short of contacting the curved inner surface hemispherical lower head section to form a radially extending, annular gap therebetween which varies in size in response to variations in the temperature of reactor coolant circulated through the pressure vessel and internals due to a difference in the coefficients of thermal expansion thereof, and strainer means comprising an annular member with apertures therethrough smaller than the smallest size of said gap secured to the lower end of said reactor internals and extending radially outward therefrom, over the gap with an outer peripheral edge in contact with the curved inner surface of the hemispherical lower head section for all sizes of said gap to prevent debris from entering and lodging in said gap from above while allowing fluid to pass therethrough. 2. The combination of claim 1 wherein said annular strainer member is a resilient member which is fixed to the lower end of said internals with said outer peripheral edge pressed against the hemispherical lower head section of the vessel and which bends to maintain said outer peripheral edge in contact with the curved inner surface of the hemispherical lower head section of the vessel as the size of the gap changes. 3. The combination of claim 2 wherein said annular strainer member is curved in cross-section with a curvature which maintains said outer peripheral edge of the resilient annular member in contact with the inner surface of the hemispherical lower head section as the gap varies in size. 4. The combination of claim 3 wherein said annular member is convex upward in cross-section to increase over a flat annular member the angle at which the strainer member intersects the curved inner surface of the hemispherical lower head section of the vessel. 5. A nuclear reactor comprising: an upright cylindrical pressure vessel having a hemispherical lower head section with a curved inner surface and defining an annular support flange extending radially inward near the upper end thereof;  a cylindrical core barrel having a radially outwardly extending flange at its upper end which seats on said support flange with the core barrel suspended inside the pressure vessel;  resilient means clamping said core barrel flange down onto said support flange;  secondary core support means depending from the bottom of the core barrel into the lower hemispherical head section and terminating at its lower end in a horizontally extending base plate which defines at its lower edges a spherical surface spaced from the inner surface of the hemispherical lower head section to define a radially extending, annular gap therebetween; and  strainer means for preventing debris from entering from above and lodging in said gap and lifting the flange on said core barrel up off of the support flange against said resilient clamping means as the core barrel and secondary core support expand more than the pressure vessel in response to heat-up of the reactor to reduce the size of said gap, said strainer means comprising an upwardly convex in cross-section, resilient, annular, member secured to the periphery of said base plate and extending radially outward therefrom over said gap to contact with a peripheral edge the inner curved surface of the hemispherical lower head section, and which bends to remain in contact therewith as said gap varies in size with temperature, said annular member defining apertures therethrough through which reactor coolant but not debris of a size which could lodge in said gap can pass into said gap from above.