Patent Number: 051320770
Section: description

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT The number 10 generally designates the improved lower end fitting constructed according to the invention. The end fitting 10 is attached by means of instrumentation tube 12 and guide tubes 14 to the remaining fuel assembly structure, as represented by lower grid 16 and fuel rods 18 partially shown in FIG. 1. A typical pressurized water nuclear reactor lower core plate 20 is shown in dotted lines in FIG. 1. Diffusing flow between the multi-holed lower core plate 20 and the multi-holed top flow plate 22 of the lower end fitting, below the fuel rods 18, are the bell mouth type flow diffusers 30. As flow in the reactor core leaves the openings 24 in lower core plate 20 it is directed to and enters the lower end and smaller ends 32 of diffusers 30. As seen in FIGS. 3 and 4, the curved shape from smaller end 32 to larger output end 34 of each diffuser 30 is a parabolic type adjusted in their bell mouth shape in a manner dictated by the particular lower core plate flow hole geometry, lower end fitting design, and the reaction flow rate to achieve maximum jet diffusion. This, in turn, produces a resultant reduction in damaging vibration of fuel rods 18 and pressure drop through turbulence. The diffusers also act to stiffen the lower end fitting 10 by being rigidly connected to the legs 36 at the corners of the lower end fitting by horizontal webs 38 which are integral with legs 36. The diffusers 30 are mounted in recesses in webs 38 defined by counterbore 40. Also adding rigidity to the lower end fitting is a wear-reduction-shield 50 mounted in a central opening 52 in web 38. The opening 52 and web 38 form a hub which provides the central opening for an in-core-instrumentation thimble (not shown). This structure will be clearly understood from reading my U.S. Pat. No. 4,888,149. It will be apparent from the drawings here presented as FIGS. 2-4, that wear-reduction-shield 50 will, when the proper relationship between lower end fitting 10 and the core plate 20 are established by pins 56 and holes 58 in web 38, act further to stiffen the end fitting 10. Moreover, the relationship of shield 50 to a counterbore 60 in top flow plate 22 and counterbore 52 is such that it will help prevent tilting or tipping of the end fitting 10 and therefore prevent legs 36 from entering holes 24 in core plate 20. Again, see my U.S. Pat. No. 4,888,149.