Abstract: In an embodiment of the present invention, the core of a nuclear reactor includes a plurality of fuel cells and a plurality of large control rods. Each large control rod is about two times the width of a conventional control rod and includes four control rod blades extending radially from a central portion and arranged at right angles to each other. The blades define four fuel bundle receiving channels. The core is configured so that the control rods are-arranged in a plurality of staggered rows with four fuel bundles in each receiving channel.

Abstract: A core plate assembly for a nuclear reactor includes a plurality of support beams, a flat plate positioned on top of the support beams, a plurality of control rod guide tube openings arranged in staggered rows, and a plurality of fuel supports extending through the flat plate. Each guide tube opening has a cruciform shape defines four fuel bundle receiving areas. Each fuel support includes a coolant flow inlet, and a coolant flow outlet sized to receive a lower tie plate of a fuel bundle. The coolant flow inlet is offset from coolant flow outlet so that a centerline of the coolant flow inlet is parallel to a centerline of the coolant flow outlet. The coolant flow inlets are positioned adjacent a support beam, and the coolant flow outlets are positioned in a fuel bundle receiving area.

Abstract: Fuel bundle and control rod assemblies for a nuclear reactor are described. In one embodiment of the apparatus, the nuclear reactor includes several conventional size fuel bundles and at least one large control rod. The large control rod includes four fuel bundle receiving channels, and each such channel is sized to receive four conventional size fuel bundles.

Abstract: Methods and apparatus for moving fuel bundles in a reactor pressure vessel (RPV) of a nuclear reactor are described. In one embodiment of the apparatus, a support tube facilitates the positioning of a multiple channeled magazine within the RPV, especially at locations adjacent fuel bundles. In the one embodiment, the support tube extends in the reactor pressure vessel into the area above the top guide. A magazine assembly is coupled to the support tube, and includes a magazine having a plurality of fuel bundle receiving channels. The magazine extends from the support tube so that it is adjacent the fuel bundles and the top guide. Grapples extend through the magazine channels, engage the fuel bundles, and retract the bundles into the magazine channels. The magazine and support tube, and thus the bundles, are then moved.

Abstract: Support assemblies for allowing RPV radial expansion while simultaneously limiting horizontal, vertical, and azimuthal movement of the RPV within a nuclear reactor are described. In one embodiment, the support assembly includes a support block and a guide block. The support block includes a first portion and a second portion, and the first portion is rigidly coupled to the RPV adjacent the first portion. The guide block is rigidly coupled to a reactor pressure vessel support structure and includes a channel sized to receive the second portion of the support block. The second portion of the support block is positioned in the guide block channel to movably couple the guide block to the support block.

Abstract: A telescoping mast with zero clearance which can be used in a fully automatic, relative positioning refueling machine. The telescoping mast consists of a series of nested tubes separated by spacers of unique design. Each spacer consists of an upper spacer assembly attached to the upper end of an inner tube segment nested in an outer tube segment and slidable inside the outer tube segment; and a lower spacer assembly attached to the lower end of the outer tube segment and slidable outside the inner tube segment. The spacer assemblies are preferably made of molded plastic, for example, polyethylene. Each spacer assembly is formed by a spacer ring and a plurality of corrugated members connected at one end to the spacer ring. The distal ends of the corrugated members of the upper spacer assembly contact the distal ends of respective ones of the corrugated members of the lower spacer assembly when the inner tube segment is in an extended position relative to the outer tube segment.

Abstract: A boiling water reactor includes a pressure vessel containing a reactor core, chimney, steam separator assembly, and steam dryer assembly therein, with the vessel being filled with reactor water to a normal water level through the steam separator assembly. A plurality of control rod drives extend downwardly from the bottom of the pressure vessel and are operatively joined to control rods extending downwardly into the reactor core. The chimney includes a plurality of channels disposed above the core and laterally spaced apart to define guide slots for receiving the control rods as they are selectively translated upwardly out of the core by the control rod drives. The chimney has a vertical height for increasing the normal water level above the reactor core and for providing a space for the control rods withdrawn from the reactor core by the bottom-mounted control rod drives.

Abstract: A removable feedwater sparger assembly includes a sparger having an inlet pipe disposed in flow communication with the outlet end of a supply pipe. A tubular coupling includes an annular band fixedly joined to the sparger inlet pipe and a plurality of fingers extending from the band which are removably joined to a retention flange extending from the supply pipe for maintaining the sparger inlet pipe in flow communication with the supply pipe. The fingers are elastically deflectable for allowing engagement of the sparger inlet pipe with the supply pipe and for disengagement therewith.

Abstract: A nozzle for joining a pool of water to a nuclear reactor pressure vessel includes a tubular body having a proximal end joinable to the pressure vessel and a distal end joinable in flow communication with the pool. The body includes a flow passage therethrough having in serial flow communication a first port at the distal end, a throat spaced axially from the first port, a conical channel extending axially from the throat, and a second port at the proximal end which is joinable in flow communication with the pressure vessel. The inner diameter of the flow passage decreases from the first port to the throat and then increases along the conical channel to the second port. In this way, the conical channel acts as a diverging channel or diffuser in the forward flow direction from the first port to the second port for recovering pressure due to the flow restriction provided by the throat.

Abstract: A phase-separator assembly for a boiling-water nuclear reactor includes a steam-separator and a dryer. The steam separator and dryer are mechanically coupled so that relative vertical movement is permitted therebetween. The mechanical coupling limits this relative vertical movement. When installed in a reactor, the steam separator and dryer are independently supported. The dryer is supported so as to define a gap between the dryer and steam separator that optimizes their collective performance. When in storage, the dryer is not independently supported. Instead, the dryer is dropped to a minimum height above the steam separator, providing for compact storage.

Abstract: A latch assembly removably joins a steam separator assembly to a support flange disposed at a top end of a tubular shroud in a nuclear reactor pressure vessel. The assembly includes an annular head having a central portion for supporting the steam separator assembly thereon, and an annular head flange extending around a perimeter thereof for supporting the head to the support flange. A plurality of latches are circumferentially spaced apart around the head flange with each latch having a top end, a latch hook at a bottom end thereof, and a pivot support disposed at an intermediate portion therebetween and pivotally joined to the head flange. The latches are pivoted about the pivot supports for selectively engaging and disengaging the latch hooks with the support flange for fixedly joining the head to the shroud or for allowing removal thereof.

Abstract: In a boiling-water nuclear reactor, a core-control assembly comprises a control rod, a fuel support, a control-rod guide tube, a control-rod drive, and a control-rod-drive housing. The fuel support is welded to the control-rod guide tube. To remove the control-rod drive, the reactor vessel can be opened and the adjacent fuel bundles removed from the fuel support. Then the control-rod can be rotated after clearing the fuel support. The control rod is then rotated to decouple its bayonet connection to the control-rod drive. The control rod can then be lifted out of the reactor. This arrangement allows a control rod to be replaced without handling of the fuel support. In addition, the fuel support can be more securely installed since it does not need to be removed.

Abstract: A natural-circulation boiling-water reactor has skirts extending downward from control rod guide tubes to about 10 centimeters from the reactor vessel bottom. The skirts define annular channels about control rod drive housings that extend through the reactor vessel bottom. Recirculating water is forced in through the low-level entrances to these channels, sweeping bottom water into the channels in the process. The sweeping action prevents cooler water from accumulating at the bottom. This in turn minimizes thermal shock to bottom-dwelling components as would occur when accumulated cool water is swept away and suddenly replaced by warmer water.