BWR fuel assembly with water flow mixing chamber at fuel bundle/water cross entrance

This patent describes a fuel assembly having a bundle of elongated fuel rods disposed in side-by-side relationship so as to form an array of spaced fuel rods. An outer tubular flow channel surrounds the fuel rods so as to direct flow of coolant/moderator fluid along the fuel rods. A hollow water cross extends centrally through and is interconnected with the outer flow channel so as to divide the channel into separate compartments and the bundle of fuel rods into mini-bundles thereof being disposed in the respective compartments. The improvement described here comprises: means defining a flow mixing chamber within and between lower end portions of the mini-bundles of fuel rods and below the water cross which allows free mixing cross flow within and between the lower end portions of the respective mini-bundles. The mixing chamber defines means including an upper limit constituted by a lower ends of the water cross and a lower limit constituted by lower end of the respective mini-bundles. The water cross lower end is spaced within the range of about six to twelve inches above the mini-bundle lower ends