Abstract: An improved ferrule spacer for use with high density fuel rod arrays within boiling water reactor fuel bundles is disclosed. Ferrules are constructed in mating ferrule pairs. Each ferrule is divided into upper and lower ferrule halves. One ferrule half has sides thereof with the walls removed. The other ferrule half has its in place. The ferrule pairs are confronted with one ferrule inverted with respect to the other and with each complete ferrule wall of one ferrule half being juxtaposed to a ferrule half at a missing wall. Preferably, and at the point of tangency between the ferrule pairs, an aperture for receiving and confining an "H" type double loop spring is defined. The disclosure includes ferrules having a circular surround for the fuel rods and ferrules having an octagon sectioned surround for the fuel rods. Each member of the ferrule pair is symmetrical and completely interchangeable to provide for both convenient assembly and a small inventory of assembly parts.

Abstract: In a fuel bundle for a boiling water nuclear reactor, modification of the spacers at the peripheral spacer band is made to maintain a more uniform spacing of the peripheral fuel rods from the channel walls to avoid critical power limitations. The conventional fuel bundle construction include a plurality of side-by-side sealed vertically disposed nuclear fuel rods in a square array supported at a lower tie plate, at least some of the fuel rods fastened to an upper tie plate, and held in designed spaced apart relation as a unitary mass by intermittent vertically placed spacers. A square sectioned channel surrounds the upper tie plate, the lower tie plate, and the fuel rods and spacers therebetween. The square sectioned channel functions to confined fluid flow interior of the fuel bundle between the tie plates and through the fuel rods. At the same time, the channel separates a core bypass region exterior of the channel having high moderator density from the flow path interior of the fuel bundle.

Abstract: A water rod is disclosed in combination with a fuel bundle for a boiling water nuclear reactor in which water is introduced to the water rod directly from the high pressure lower plenum below the reactor core. This introduced water circulates upwardly and centrally through the water rod to the top of the water rod. Thereafter, the water flows peripherally downward adjacent the exterior of the water rod. The introduction of water to the water rod directly from the high pressure water plenum below the reactor core provides sufficient pressure to maintain water flow through the water rod and to prevent flashing of the water passing through the circuitous path of the water rod to steam. Thereafter, the water is discharged at the bottom of the fuel bundle with water entering the steam generation path through the lower tie plate so that the discharged water participates in the steam generating flow path within the fuel bundle.

Abstract: Part length water regions are located above part length fuel rods in boiling water nuclear reactor fuel bundles. The part length water regions include discrete containers having entry ports at the top of the part length water regions for capturing water, and vent ports for permitting internally generated steam to escape. The advantages of improved neutron moderation in the upper portion of the fuel assembly are maintained while the uranium fuel removal requirements are minimized.

Abstract: A fuel bundle for a boiling water nuclear reactor having an improved water rod is disclosed, this water rod having two discrete compartments upper and lower for containing water. The bottom compartment flows moderator from the bottom of the fuel bundle through the water rod compartment to discharge points located through the water rod side walls between the upper most spacers; the top compartment opens upwardly and is naturally filled with liquid moderator settling out of the upwardly flowing moderator during reactor operation. There results the requisite presence of liquid moderator within the water rod for supplying the upper two phase region of the fuel rod with nearly full moderator density. At the same time, water flow through of the water rod from the bottom of the fuel bundle to the upper two phase region of the fuel bundle improves the thermal hydraulic performance.

Abstract: In a fuel bundle for use in the core of a boiling water nuclear reactor, part length rods having a tendency to reduce pressure drop are used in combination with spacers and spacer attached devices tending to restore pressure drop to improve critical power. The addition of the part length rods has the advantage of lowering the pressure drop. Attached devices substantially recapture the pressure drop. Exemplary spacer attached mechanisms for the recapture of pressure drop are set forth including vanes--preferably swirl vanes on the spacers, decreasing the spacer pitch to increase the total number of spacers in the upper two phase region of the fuel bundle, increasing the vertical height of the spacers, and increasing the thickness of the metal from which the spacers are constructed. Two classes of separation devices are disclosed for placement in the volume overlying the end of the partial length fuel rods.

Abstract: A fuel bundle is disclosed in which interspersed part length fuel rods define between the end of the fuel rods and the upper tie plate void regions which are not otherwise occupied. Full length fuel rods adjacent to these regions are provided with an expanded upper plenum region which effectively increases the fuel rod diameter at the end of the upper two phase region of the fuel bundle. Under normal circumstances and a fuel bundle with only full length fuel rods, such an expansion of the upper regions of the fuel rods would cause unacceptable pressure drop. Where such expansion occurs adjacent the vacated volumes created by the part length fuel rods, unacceptable pressure drop does not occur. Consequently, and with the expanded plenum volume, a longer length of active fuel pellets can be accommodated within the full length fuel rods.

Abstract: An improved spacer is disclosed which contains an Inconel grid and a Zircaloy surrounding band. The Inconel grid can be fabricated from the extremely thin and highly elastic spring metal utilizing a modification of a prior art cell construction that includes paired inwardly bent vertical spring legs with cantilevered and rod encircling upper and lower arm pairs The spring legs extend at spaced apart locations between the upper and lower arm pairs and have a medial spring rod contacting portion for biasing the rods into stops on the rod encircling arm pairs. The springs at the upper and lower ends are provided with spring dimple stops to prevent over stressing of the spring during assembly or handling of the fuel bundle into which the spacer is incorporated. The rod encircling arm pairs have an offset from center where the two arms meet at their distal ends to complete encirclement of the rods. This offset from center enables the cells to be fastened in cell pairs at their respective embracing arms.

Abstract: A swirl vane is disclosed for addition to a spring metal grid spacer utilized with a conventional nuclear boiling water nuclear reactor. The spring metal spacer includes a matrix of fuel rod containing cells. Each cell has at least one spring leg and at least two fuel rod encircling arms. The spring leg functions to bias a fuel rod contained within the cell at the spacer to one side of the cell. The two rod encircling arms define stops against which the fuel rods are biased. The cells themselves are welded into a unitary matrix and preferably surrounded by a metallic band. The improved swirl vane of this invention includes an "I" shaped spring steel strip. This strip includes top and bottom tabs for engaging the respective top and bottom grid structure of the spacer. The "I" shaped strip is then twisted to provide the swirl vane surface, this twisting being preferably slightly less than or greater than the total twisting required.

Abstract: A method and apparatus for improving the operating efficiency of a boiling water reactor is disclosed. Instead of coolant water being injected simultaneously at the bottom of the fuel rod assemblies and core bypass regions, the two flows then proceeding in parallel to the top of the reactor, the top of the bypass regions is sealed off and bypass coolant water is directed at the bottom of the sealing cover. This forces the bypass coolant water to flow down through the bypass regions. At the bottom of the bypass regions, provision is made to allow the bypass water to flow into the bottom of the fuel rod assemblies where it is entrained by the fuel rod coolant water flow. By converting flow through the core bypass region into a single series flow, increased operating efficiency is achieved.

Abstract: In a boiling water reactor having discrete bundles of fuel rods confined within channel enclosed fuel assemblies, an improved fuel design of bundles of fuel rods interior of the channels is disclosed. Specifically, partial length rods are utilized which extend from the bottom of the channel only part way to the top of the channel. These partial length rods are symmetrically distributed throughout the fuel bundle with the preferred disposition being in the second row of the bundle of fuel rods from the channel wall. The symmetrical distribution of the partial length rods is at spaced apart locations one from another. During shutdown of the reactor, an improved cold shutdown margin is produced at the top of the fuel assembly due to the improved moderator-to-fuel ratio and reduction in plutonium formation at the upper portion of the bundle. Shutdown control rod worth is improved due to greater moderator-to-fuel ratio and a longer thermal neutron diffusion length.

Abstract: A light water nuclear reactor test assembly for emulating the performance of a nuclear boiling water reactor fuel bundle and measuring the subchannel void fraction in the two-phase region of the emulated fuel bundle by gamma ray attenuation is disclosed. The emulated fuel bundle has individual emulated nuclear fuel rods typically heated by individual electrical currents instead of nuclear reaction and are cylindrically hollow. A gamma-emitting source is placed on a probe and mounted for vertical excursion inside a selected emulated hollow fuel rod. A detector, typically a Geiger-Muller counter, is placed for corresponding vertical excursion inside another and preferably adjacent fuel rod. Gamma radiation from the source to the detector through the walls of the emulated fuel rods is measured. Preferably, both detector and source are collimated so that the detector does not receive gamma ray scattering from the interior of the test assembly.

Abstract: An improved spacer is disclosed which contains an Inconel grid and a Zircaloy surrounding band. The Inconel grid can be fabricated from the extremely thin and highly elastic spring metal utilizing a modification of a prior art cell construction that includes paired inwardly bent vertical spring legs with cantilevered and rod encircling upper and lower arm pairs. The spring legs extend at spaced apart locations between the upper and lower arm pairs and have a medial spring rod contacting portion for biasing the rods into stops on the rod encircling arm pairs. The springs at the upper and lower ends are provided with spring dimple stops to prevent over stressing of the spring during assembly or handling of the fuel bundle into which the spacer is incorporated. The rod encircling arm pairs have an offset from center where the two arms meet at their distal ends to complete encirclement of the rods. This offset from center enables the cells to be fastened in cell pairs at their respective embracing arms.

Abstract: In a boiling water reactor having discrete bundles of fuel rods confined within channel enclosed fuel assemblies, an improved fuel design of bundles of fuel rods interior of the channels is disclosed. Specifically, partial length rods are utilized which extend from the bottom of the channel only part way to the top of the channel. These partial length rods are shortened with respect to the remaining rods and are symmetrically distributed throughout the fuel bundle with the preferred disposition being in the second row of the bundle of fuel rods from the channel wall. The symmetrical distribution of the partial length rods is at spaced apart locations one from another. The partial length rods extend from the bottom of the fuel bundle and terminate within the boiling region. during shutdown of the reactor, an improved cold shutdown margin is produced at the top of the fuel assembly due to the improved moderator-to-fuel ratio and reduction in plutonium formation at the upper portion of the bundle.

Abstract: An improved upper tie plate is disclosed in a fuel bundle for a boiling water nuclear reactor. The tie plate resides in a fuel bundle including an upper tie plate, a lower tie plate, a matrix of sealed fuel rods supported therebetween, and a surrounding channel. Both the lower tie plate and the improved upper tie plate have two functions; they support the fuel rods in vertical upstanding relation between the tie plates and interior of the channel and permit the passage of moderating coolant through the channel from the bottom of the channel to the top of the channel. This moderating coolant enters through the lower tie plate in the liquid form, passes into the matrix of upstanding fuel rods where steam is generated and exits outwardly through the improved upper tie plate as a water steam mixture at the top of the fuel bundle.

Abstract: A combination of flow trippers with spacer deflectors in the two phase steam/water region of a fuel bundle in a boiling water reactor is disclosed. Spacers with deflectors are placed immediately above the flow trippers. The flow trippers are located on either an inside channel wall surrounding the fuel bundle or the outside of water chambers within the fuel bundle. Additional flow trippers may be located adjacent to the spacers, above the flow trippers that are below the spacers. The spacers are provided with deflector skirts overlying the flow trippers. In operation of the fuel bundle, excess water flows in the two phase region in a film on the unheated inside walls of the fuel channel or the outside walls of the water chambers. The film flow is perturbed by the flow trippers and is deflected toward the fuel rods. The overlying deflector skirts or tabs on the spacers further deflect the liquid toward the fuel rods to improve cooling and to increase the power generation capability of the fuel bundle.

Abstract: An improved channel is disclosed which has a reduced average thickness in its upper portion. The lesser average thickness corresponds to a lower pressure difference acting on the channel sides, over the upper portion of the channel. The reduction in average thickness is accomplished by cutting flow trippers into the inner surface of the channel walls and/or cutting grooves into the outer surface of the channel. The axial variation of channel average thickness increases water volume adjacent to the upper part of the channel to provide increased neutron moderation, to minimize the steam void reactivity coefficient, and to provide a greater cold shutdown margin. The material removed to produce the flow trippers increases the cross-sectional area inside the channel and reduces pressure drop in the upper portion of the channel. The flow trippers divert water flowing on the channel walls to the fuel rods adjacent to the channel walls, permitting higher reactor power operation.

Abstract: In a nuclear reactor fuel assembly, a relatively flexible mounting member for mounting a large coolant conducting tube to the lower tie plate whereby excessive side forces on the fuel rod spacers are avoided in the event of lateral displacement of the fuel assembly such as during a seismic event.

Abstract: In a fuel assembly for a nuclear reactor a fuel element spacer formed of an array of laterally positioned cojoined tubular ferrules each providing a passage for one of the fuel elements, the elements being laterally supported in the ferrules between slender spring members and laterally oriented rigid stops.

Abstract: An improved channel is disclosed which has a reduced average thickness in its upper portion. The lesser average thickness corresponds to a lower pressure difference acting on the channel sides, over the upper portion of the channel. The reduction in average thickness is accomplished by cutting flow trippers into the inner surface of the channel walls and/or cutting grooves into the outer surface of the channel. The axial variation of channel average thickness increases water volume adjacent to the upper part of the channel to provide increased neutron moderation, to minimize the steam void reactivity coefficient, and to provide a greater cold shutdown margin. The material removed to produce the flow trippers increases the cross-sectional area inside the channel and reduces pressure drop in the upper portion of the channel. The flow trippers divert water flowing on the channel walls to the fuel rods adjacent to the channel walls, permitting higher reactor power operation.