Nuclear fuel assembly with axial guide tubes - whose upper ends attach to a plate axially slidable inside upper sleeve to accommodate tube deformation

摘要

A nuclear fuel assembly comprises a framework consisting of circumferentially spaced guide tubes (16) attached to upper and lower sleeves, the tubes extending through apertures in grids spaced axially between the sleeves and accommodating fuel rods in other said apertures. The guide tubes (16) are fixed to the lower sleeve, but their upper ends are secured to a transverse plate (32) which is axially slidable inside the upper sleeve against spring loading. Pref., the upper sleeve has a main cylindrical section and a lower section which widens downwards to a hexagonal base. The lower section has outlet openings (38) for coolant flow. A ring (48) secured inside the sleeve at the bottom of the main section limits downward movement of plate (32). Plate (32) is urged downwards by an array of helical springs (46) axially aligned with respective tubes (16). An upper transverse plate (42) is fixed across the sleeve. Tubes (54) depend from plate (42) towards plate (32) and act as extensions of tubes (16) for guiding of control rods as well as supports for the springs (46), which abut plate (42). Rods (44) also depend from plate (42) through holes in plate (32) to guide the axial sliding of plate (32). USE/ADVANTAGE - Fuel assembly in light water cooled and moderated nuclear reactor. While the top of the upper sleeve is braced against a fixed upper part of the reactor core support, the plate (32) is movable to accommodate any deformation of tubes (16).