Combustion Engineering, Inc.

Combustion Engineering Co., Inc.

Andrew J Anthony

Malcolm Duane Groves

Richard H Young

John Jefferson Hutchinson

Kenneth A Martin

Malcom D Groves

An improved nuclear fuel assembly (10) of the type having a plurality of intersecting metal strips (14) welded at the strip intersections (32). At least some of the strips (16a, 18a) have nonlinear upper or lower edges (32a, 44a) at the intersections such that some of the intersection welds (34) at the strip upper or lower edges are at different elevations (34b) relative to intersection welds at other upper or lower edges (34a, 34c, 34d).

High strength nuclear fuel grid

An inproved grid (16) for a nuclear fuel assembly (10), having a plurality of externally projecting, integrally formed anti-bowing springs (50) spaced about the grid perimeter plate (26), for interacting with flat surfaces (52') on the opposite grids (16') of adjacent assemblies (10'). The anti-bowing springs (50) are horizontally separated along each grid (26) in periodic alternation with substantially flat portions (52) of the perimeter plate (26). Preferably, each grid has a plurality of primary anti-bowing springs (70) that project a distance at least equal to the nominal gap (g) between assemblies, and a plurality of secondary anti-bowing springs (72) that are stiffer but project less than the primary springs. Also, backup springs (74) are disclosed as integrally formed ridges adjacent to the anti-bowing springs. The interaction of each grid (16) with its neighbor (16') 'tightens' the core during power operation and provides an anti-bowing effect.

Anti-bow grid for nuclear fuel assembly

A debris catching strainer grid for capturing and retaining deleterious debris carried by reactor coolant before it enters the active region of a fuel assembly and creates fuel rod cladding damage has a plurality of fuel end cap compartments defined by pairs of first and second intersecting and slottedly interlocked grid-forming strips attached to a perimeter member and to each other. The end cap compartments defined by strips including vertical rows of integral leaves on opposite sides of the strip or by pairs of adjacent integral leaves intermediate their intersections. In the latter case, each leaf of the pair of leaves is the mirror image of the other leaf of the pair with an asymmetric shape with the greatest distance of projection out of the plane of the strip remote from the midpoint of the strips between their intersections.

Debris catching strainer grid

The present invention is directed to a method for increasing the wear and corrosion resistance of zirconium and zirconium alloys by ion implantation. In particular the present invention is directed to the ion implantation of nitrogen and/or carbon for the purpose of increasing wear resistance; and the ion implantation of arsenic, carbon, chromium, nitrogen, tin, phosphorus or combinations thereof for the purpose of increasing the corrosion resistance.

Ion-implantation of zirconium and its alloys

A neutron streaming shield comprising a plurality of wire mesh baskets, each basket located between two adjacent vessel nozzles, the total area of the nozzles and baskets being sufficient to intercept any streaming neutrons. The baskets are substantially filled with a multiplicity of randomly packed lumps of a neutron attenuating material, preferably a borated-hydrogenated-argillaceous media. Since the basket is somewhat flexible, it can be inserted in the annulus above the nozzles and then filled with the lumped material, forming a plurality of barriers to compliment the attenuating affect of the nozzles, such that any streaming neutrons will be stopped either by the nozzles or the lumped material in the baskets.

Neutron streaming shield for nuclear vessel cavity

Repaired fluid conveying tubes are tested for leaks by isolating the repaired region from the remainder of the tube and then pressurizing the isolated region with a suitable gas. The isolation is accomplished by axial compression of one or a pair of seals which expand radially when subjected to axial force.

Leak detection method and apparatus

Nuclear fuel assemblies having square cross-sections mount tubes at each corner, the tubes containing springs which are extended through apertures in the tube walls when actuated by solid rods extended down into the tubes by the weight of the upper guide structure of the nuclear vessel in which the fuel assemblies are mounted. The springs, extended from strategically located positions along the length of the tubes, engage the surface of adjacent fuel assemblies to dimensionally stabilize the fuel assemblies relative to each other and the vessel in which they are mounted.

Lateral support for nuclear fuel assemblies

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.

Method for determining clad integrity of a nuclear fuel rod

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.

Arrangement for retaining a fuel rod in a reconstitutable fuel assembly

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. The post, however, offers an absolute limit for the upward movement of the sleeve and thereby acts as a redundant vertical stop to prevent the sleeve from becoming dislocated within the post.

Sleeve connection for reconstitutable control rod guide tube

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.

Nuclear fuel assembly holddown apparatus

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.

Bottom mounted fuel holddown mechanism

A bimetallic spacer means designed to be cooperatively associated with a nuclear fuel assembly and operative to resist the occurrence of in-reactor bowing of the nuclear fuel assembly. The subject bimetallic spacer means in accord with one embodiment of the invention includes a member formed, at least principally, of zircaloy to which are attached a plurality of stainless steel strips. The latter stainless steel strips are located on the external surface of the zircaloy member and with the major axis of each of the plurality of stainless steel strips extending substantially perpendicular to the major axis of the zircaloy member. In accord with another embodiment of the invention, the subject bimetallic spacer means includes a member formed at least principally of zircaloy to which a plurality of stainless steel strips are attached so as to be positioned thereon externally thereof and with the major axis of each of the plurality of stainless steel strips extending substantially parallel to the major axis of the zircaloy member. In accord with a further embodiment of the invention, the stainless steel strips are attached to preselected members, each embodying at least a cladding of zircaloy, which are located in the rows of fuel rods that define the perimeter of the fuel matrix of the nuclear fuel assembly. In each of the embodiments, the stainless steel strips during power production expand outwardly to a greater extent than do the members to which the stainless steel strips are attached, thereby forming stiff springs which abut against like bimetallic spacer means with which the other nuclear fuel assemblies are provided in a given nuclear reactor core to thus prevent the occurrence of in-reactor bowing of the nuclear fuel assemblies. Namely, the stainless steel strips expand laterally relative to the fuel assembly and thereby occupy the space adjacent to the external surface of the fuel assembly, into which portions of the fuel assembly would otherwise be receivable should they undergo bowing.

Bimetallic spacer means for a nuclear fuel assembly

An earthquake resistant apparatus for storing nuclear fuel within a water-filled pool wherein a structural grid which supports the fuel is in turn supported by cables from an upper elevation. The grid is located below the water level and spaced from the walls of the pool an amount, preferably at least equal to the anticipated earthquake displacement. The grid is located below the water level a sufficient depth for radiation shielding during fuel handling and storage, and tension members are preferably ten times the design earthquake displacement. A horizontal baffle is located around the periphery of the pool at an elevation above the grid.

Nuclear fuel storage apparatus for seismic areas

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.

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Tariffville, CT, United States of America

Andrew J Anthony