Abstract: Disclosed is a means for increasing coolant flow through the areas adjacent to where the removable top head closure is bolted to the body of pressurized water nuclear reactor. A circumferential plenum for coolant is provided between the upper flange of the core barrel, the inner wall of the pressure vessel body and the upper circular support plate and providing a plurality of orifices for coolant in the upper flange of the core barrel and the upper circular support plate whereby a coolant may be circulated through the core barrel flange, the circumferential plenum and the upper support plate and into the space enclosed by the removable top closure head.

Abstract: A method for limiting movement of a thermal shield of a nuclear reactor, and a thermal shield displacement limiter therefor, is provided where at least four and preferably six or more key-way inserts are positioned in pockets machined in the upper portion of a thermal shield, and bolted and doweled to the thermal shield. Each key-way insert is engaged by a limiter key that is bolted and doweled to the core barrel to tangentially restrain movement of the thermal shield relative to the core barrel, while allowing radial and axial movement to the thermal shield relative to the core barrel. Preferably, lock pins extend diametrically through the bolts and dial pins and engage the key-way insert and limiter key, respectively, to lock the bolts and dowels in position, and the engaging surfaces between the key-way inserts and the limiter keys are wear hardened.

Abstract: To preclude failure of components of control-rod assemblies or of unprotected control rods (WDRC's) a calandria is provided above the upper internals. The calandria includes hollow tubes through which the drive rods for the various control rods pass and which protect the drive rods. The guides for the control rods are closed except at the top so that the coolant flows vertically through the guides into the calandria. In the calandria, the coolant flows transversely to the hollow tubes and out through the outlet nozzle. The tubes have a mass and stiffness and strength such that they resist failure by reason of the transverse flow of the coolant to which they are subjected.

Abstract: A lateral restraint device for nuclear fuel racks which can accommodate differential thermal expansion between the racks and a containing enclosure. The restraint includes a piston, movable within a cylinder, joined to one or more support pads which contact the wall of the enclosure. A spring is also provided within the cylinder to act upon the piston. The piston is sized to provide a predetermined clearance or opening allowing controlled liquid flow into the cylinder. The piston can be held in a given position within the cylinder with the spring compressed to facilitate installation onto the side of a fuel rack, and subsequently positioned by the expanded spring. Relatively small differential expansion loads are accommodated by the moving piston and spring, while large loads, such as those imposed by a seismic occurrence, are resisted by the hydraulic fluid within the cylinder.