Abstract: A core shroud including flexible panels sealingly attached to the inner surface of the shroud at an elevation opposite the fuel assembly grids nearest the core midplane. Each panel forms the outer wall of a deformable chamber which is pressurized through a conduit carried by the shroud. One end of the conduit is in fluid communication with the reactor coolant at a high pressure location remote from the panels, producing a pressure differential across the panel which urges the panel against the adjacent grid to prevent core bowing.

Abstract: A method for testing the clad integrity of a nuclear fuel rod, comprising the first step of fabricating a sealed fuel rod with a wad of electrically conducting material mounted therein. The material is of a type that undergoes a permanent change in electrical conductivity when exposed to water. The next step is to establish an eddy current signal characteristic of the moisture-free rod. The rod is then loaded into the core as part of a fuel assembly. After the producing power, the assembly is removed for inspection, and an eddy current signal is again obtained from the rod. The eddy current signals are compared to determine whether inleakage of moisture has oxidized or otherwise altered the conductivity of the wad enough to significantly change the characteristic signal.

Abstract: An improvement in fluid pressure transducers having a housing with oppositely facing magnetic blocks (12,14) that form a sealed chamber (20) in which a magnetically permeable diaphragm (24) is disposed for magnetic coupling with electromagnetic coils (30) mounted within the blocks. The coil is mounted on an elongated plug (34) and covered by a non-magnetic, unitary metal cap (36) that is flexibly sealed between the chamber and the coil. The cap has a generally cup-like inner portion (48) for covering the coil and a flat rim portion (46) that is sealingly (58) secured between the mounting plug and shoulder means (50,60) within the block.

Abstract: An improved nuclear fuel assembly in which the lowermost grid is located close to the lower end fitting of the assembly, and a conventional Zircaloy-clad fuel rod is fitted with a stainless steel tip having a bevelled notch thereon for engaging resilient means on the grid within about one inch (2.5 cm) from the lower tip of the fuel rod. The notch mechanically restrains the fuel rod from lifting upwards during reactor operation, yet is shallow enough to permit removal of the fuel rod in the event reconstitution is required. The stainless steel tip is mechanically secured to the Zircaloy end cap of the fuel rod, and is located in a low importance flux region of the core so that the higher neutron poison absorption cross section of stainless steel is of little consequence. Since the lowermost grid secures each fuel rod within one inch of the lower end of the rod, there is little likelihood that the coolant flowing over the lower ends of the fuel rods will induce significant vibrations.

Abstract: In a nuclear reactor having at least two control rod groups residing in the core for controlling the power level generated by the core, wherein one group is at a higher elevation in the core than the other, an improved method of controlling the core axial power distribution.

Abstract: A circuit for compensating the temperature dependence of the deformation properties of a pressure transducer sensor, having four basic parts: a current source having an output proportional to the sensor temperature, a constant voltage source, a Norton divider, and an operational amplifier. One brach of the Norton divider is a variable conductance ladder having an output current which increases at a programmed rate as the current from the temperature dependent source increases. The programmed rate is based on the temperature-dependent characteristic of the transducer sensor. The two branches of the Norton divider are connected as inputs to the operational amplifier. The operational amplifier provides the output of the compensating circuit, which is the difference between the reference voltage of the voltage source and the voltage at the output of the variable conductance ladder.

Abstract: A box insert for receiving nuclear fuel is formed from a plurality of vertically extending plates arranged as an open-ended polygonal container having a smaller cross-sectional area than the opening where the box is to be located in the fuel storage rack. Each plate has a flat portion forming a respective side of the container and an integral tab portion rigidly projecting outwardly from the longitudinal edge of the plate. The adjacent tabs of each plate are connected, thereby giving the container rigidity and providing the container with a plurality of outwardly projecting ribs. When the boxes are located in the rack, the ribs fit into the corners of openings and maintain the container in proper spaced relation relative to the side walls of the opening.

Abstract: A heat treating process for homogenizing high nickel alloy material so that the carbon is stabilized in the form of carbides having chromium-sufficient "envelopes". A heavily coldworked intermediate sized tube is annealed by a continuous conveyor furnace for about 20 minutes at a temperature of about 1350.degree. F. The stabilized product is then cold worked to final size and annealed at a temperature about 1485.degree. F., without the occurrence of sensitization and the associated susceptibility to corrosion attack. The final product has extremely fine grain size and the carbides are distributed throughout the grains. The method is also suitable for use on other austenitic alloys.

Abstract: A reconstitutable nuclear fuel assembly is improved by the placement of a wear sleeve within the control rod guide tube and below the removable guide tube post. The improvement comprises the guide tube having an internal ledge at its upper end from which a flanged, thin-walled metal cylindrical sleeve is suspended. The cylinder is expanded into firm contact with the inner wall of the guide tube over substantially the entire length of the cylinder. The friction fit provided by the firm contact prevents the sleeve from being pushed upward by the flow of coolant through the tube, while the flange and ledge prevent any downward movement of the sleeve in the tube. The flange on the ledge is located in spaced vertical alignment with the lowermost internal portion of the post. Thus, as the sleeve thermally expands it moves upward into the space.

Abstract: A bi-metallic spacer grid having a Zircaloy perimeter strip consisting of oppositely facing, thin walled metal plates for closely surrounding the array of fuel rods. A rigid, stainless steel cross member extends between internal surfaces of the oppositely facing perimeter plates. In the preferred embodiment, the perimeter plates have cantilevered portions extending above and below the main body of the perimeter strip. The cross members interact with the enlarged portion by urging them outward relative to the perimeter strip as the fuel assembly heats up during operation. The outwardly projecting interface surfaces of each assembly mechanically interact with the interface surfaces of adjacent assemblies providing a mechanical restraint which limits bowing of the assembly. The effectiveness of the spacer grids in limiting bowing is therefore not dependent upon controlling the mechanisms responsible for causing bow.

Abstract: An accurate determination of whether the reactivity of individual spent fuel assemblies exceeds a threshold value is made while each assembly is being transferred from the reactor core to the fuel storage rack. The reactivity of each spent assembly is compared with that of a standard assembly by comparing the subcritical multiplication resulting from insertion of a neutron source into the assemblies. The measuring apparatus preferably exteriorly resembles a control element assembly wherein one control element finger containing the neutron source is yoked to another finger containing a neutron detector. The fingers are simultaneously inserted into a standard assembly having a known reactivity and subcritical multiplication, and the resulting flux signal is recorded. Thereafter spent assemblies are sequentially measured to assure that no assembly having a subcritical multiplication greater than that of the standard is ever placed into the storage rack.

Abstract: An improved guide tube post which decreases the flow induced vibration of a cylindrical control rod suspended therethrough. The inner wall of the post, near where it exits into a diffuser region, is provided with a polygonal cross section. When, due to random fluctuation, the rod assumes an eccentric position near the wall of the post, the polygonal post geometry provides a relatively large angle between the post wall and the surface of the rod near the wall. It has been found that if this angle is too small, strong secondary flows develop along the length of the control rod and interact with other vortices in the diffuser region, to produce the vibration driving force. The polygonal cross section in the post modifies the secondary flow to reduce the intensity of the interaction with the diffuser vortices.

Abstract: A machine for smoothly and controllably winding or unwinding a stiff in-core-instrument tube onto and off of a reel during ythe refueling of a nuclear reactor. The machine includes a frame (33) and a circular reel (32) having a substantially continuous helical groove (44) extending around the circumference of the reel. The groove is adapted to receive the tube (14). A plurality of cam rollers (52) are carried by the frame and closely spaced around the circumference of the reel. The rollers keep the tube in the groove whereby the tube may be more easily wound onto or off of the reel. In the preferred embodiment, the reel carries a disposable cartridge (46) in which the grooves are formed.

Abstract: A control rod having a spring device on its lower end for eliminating oscillatory contact of the rod against its adjacent guide tube wall. The base of the device is connected to the lower tip of the rod. A plurality of elongated extensions are cantilevered downward from the base. Each extension has a shoulder for contacting the guide tube, and the plurality of shoulders as a group has a transverse dimension that is preset to be larger than the inner diameter of the guide tube such that an interference fit is obtained when the control rod is inserted in the tube. The elongated extensions form an open-ended, substantially hollow member through which most of the liquid coolant flows, and the spaces between adjacent extensions allow the flow to bypass the shoulders without experiencing a significant pressure drop.

Abstract: A fuel assembly having a lower end fitting and a spidered actuating rod interacting therewith for holding the assembly down on the core support stand against the upward flow of coolant. Locking means and bracing means for interacting with projections on the support stand are carried by the lower end fitting and are actuated by the movement of the actuating rod operated from above the top of the assembly. The locking means include weak springs mounted near some but not all of the end fitting posts, for engaging the support stand. Stiff springs are mounted internal to the other posts, for uring the posts against adjacent support stand projections to provide a bracing for the locking means as the spider portion of the actuating rod presses against the locking spring. The angle and spring rate per unit length of the bracing spring are preset to assure a fairly constant locking force during the life of the assembly.

Abstract: A fuel assembly having a lower end fitting and actuating means interacting therewith for holding the assembly down on the core support stand against the upward flow of coolant. Locking means for interacting with projections on the support stand are carried by the lower end fitting and are actuated by the movement of an actuating rod operated from above the top of the assembly. In one embodiment of the invention the downward movement of the actuating rod forces a latched spring to move outward into locking engagement with a shoulder on the support stand projections. In another embodiment, the actuating rod is rotated to effect the locking between the end fitting and the projection.

Abstract: A control rod suspended to reciprocate in a guide tube of a nuclear fuel assembly has a hydraulic bearing formed at its lower tip. The bearing includes a plurality of discrete pockets on its outer surface into which a flow of liquid is continuously provided. In one embodiment the flow is induced by the pressure head in a downward facing chamber at the end of the bearing. In another embodiment the flow originates outside the guide tube. In both embodiments the flow into the pockets produces pressure differences across the bearing which counteract forces tending to drive the rod against the guide tube wall. Thus contact of the rod against the guide tube is avoided.

Abstract: A wear sleeve for a guide tube in a nuclear fuel assembly, and a method of installing the sleeve. The sleeve is an elongated metal cylinder having an upper portion adapted to be suspended from the upper end of the guide tube, and a lower portion adapted to be permanently deformed into interference fit with the walls of the guide tube whereby the sleeve may be secured against vertical movement. The method of installing the sleeve includes the steps of suspending the sleeve from the upper end of the guide tube, then expanding a selected lower surface of the sleeve until the sleeve is permanently deformed, whereby an interference fit between the sleeve and tube is formed.

Abstract: A nuclear fuel assembly having an improved fuel rod of the type having a column of hollow pellets. A plurality of spacer plugs are interposed between proximate pellets at selected elevations along the fuel rod in order to trap pellet debris that would otherwise fall through the passage in the center of the column and accumulate at the bottom of the fuel rod. Thus, an undesirable power peak at the bottom of the fuel rod is avoided. In the preferred embodiment, the plugs are located at the same elevations as the fuel assembly grids, where the local flux is lowest and the effect of the plugs on the power distribution is minimized. The plugs could be made from any material, but graphite or a low enrichment UO.sub.2 pellet are preferred.

Abstract: A method and apparatus for removing, in an essentially continuous operation, the control rods and the upper guide structure from a nuclear reactor vessel during refueling. The apparatus includes a rigid frame which is secured to the upper guide structure after the vessel head is removed. A platform is vertically reciprocable within the frame and is adapted to engage and lift simultaneously all control rod drive shafts to a maximum elevation within the frame. A mechanical interface between the platform and the frame is provided so that continuation of the lifting force on the platform transfers the lift force to the frame whereby the upper guide structure is lifted out of the vessel. Automatically operated stop means are provided to lock the platform and rods in the maximum elevation within the frame in order to prevent accidental dropping of the rods during transfer of the upper guide structure and control rods to a temporary storage area.