Patent Number: 047755105
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The numeral 10 generally designates the hollow flow deflector of the invention. It is illustrated in FIG. 1 as being mounted on a cylindrical element of a fuel assembly 12 which may typically be a thimble or guide tube of anuclear fuel assembly but which also may be one or more of the cylindrical fuel rods, poison rods or elements 14 making up the square matrix schematically shown in FIG. 2. The cylindrical fuel assembly element or thimble 12 and the fuel rods or poison rods 14 are supported in well-known manner intermediate their ends by a fuel support grid made up of orthogonal strips 16 and 18 as schematically shown in FIG. 1. Ideally, the hollow flow deflector is mounted on the cylindrical fuel assembly element between grids, as shown in FIG. 1, in order to provide the desired subchannel mixing. The hollow flow deflector 10 includes an elongated hollow body with a central cylindrical opening 20 for engaging a cylindrical fuel assembly element 12 in tight fitting relationship therewith. As previously pointed out, while the hollow flow deflectors 10 are capable of attachment to any or all members of the fuel assembly, they are most conveniently mounted on each of these non-fuel bearing members or control element guide tubes 12. The deflectors can be attached to the hollow tubes by means of welding, bulging or other mechanical means. The hollow flow deflector 10 has an upstream end portion 22 of a first diameter or overall transverse outer dimension. The term "upstream" originates from the fact that flow of coolant through the fuel assembly is from bottom to top, in a direction parallel to the axis of the cylindrical fuel assembly elements 12 and 14. The body of the hollow flow deflector 10 also includes a downstream end portion 24 of a second and greater overall transverse dimension and an intermediate transition portion 26 joining the upstream end portion 22 with the downstream end portion 24. The flow deflector 10 includes a plurality of flow channels or grooves 30 regularly spaced about the periphery of its body. As shown in FIG. 2, the flow channels are conveniently made concave in cross-section and extend at least through the transition portion and the downstream end portion. The cylindrical central opening 12, of course, extends through and from the upstream end portion through the transition portion into and through the downstream end portion to permit its mounting on the cylindrical fuel assembly element, whether it is a thimble 12 or a fuel rod 14. The flow deflector 10 is conveniently machined from a length of zircalloy tubing such that the flow channel 30 may be easily machined and the varying transverse outer dimensions of the upstream end portion 22, the transition portion 26, and the downstream end portion 24 can be provided without the expense of complexly shaped dies. The cutting tool marks from the machining operation are visible from a close inspection of the hollow flow deflector 10. Thus, it will be seen that a hollow coolant flow deflector 10 is provided for diverting the flow of coolant fluid from one subchannel to another in order to promote mixing of the fluid. The deflectors are to be positioned at selected locations such that the vane projections formed by the flow channels 30 operate in regions of coolant flow of the fuel assembly where thermal hydraulic performance can be improved by local turbulence production, local coolant flow deflection or fuel assembly coolant flow deflection. The hollow deflectors 10 can be employed with the support grid structures to create a more effective mixing of the coolant without creating an objectionable degree of pressure-loss as the coolant flows through the reactor core, thereby resulting in reduced pumping requirements and concomitant plant operating costs. Flow visualization tests and laser velocity measurements were performed with one hollow flow deflector design in a 7.35:1 scale, 6.times.6 matrix flow model in an air test facility. During the flow visualization tests, it was observed that the flow was deflected into the adjacent subchannel at the downstream end portion of the deflector. Based upon the laser velocity measurements, it was observed that at a distance of one hydraulic diameter after the deflector, the turbulence level in the guide tube subchannel was increased by up to 50% and the flow was slanted towards the guide tube in the wake of the deflector, filling the void adjacent to the guide tube. At a distance of five hydraulic diameters after the deflector, the velocity profile and turbulence levels returned to the normal valves without the deflector. Thus, the flow deflection and increased turbulence in the vicinity of the hollow flow deflector clearly will improve the heat transfer between the fuel adjacent to the guide tube and the moderating coolant medium in that region.