Patent Number: 053717686
Section: abstract

In a boiling water nuclear reactor fuel bundle, the use of a shortened ferrule spacer in combination with overlying swirl vanes is set forth. In the preferred embodiment, the shortened ferrule spacer is placed under any swirl vanes and has an individual ferrule surrounding each fuel rod at the elevation of the spacer. Each ferrule is given both minimum side wall thickness in the range of 0.020 inches or less as well as reduced height in the order of 0.9 inch or less. The reduced height and thickness of the ferrule spacer is required to maintain pressure drop within acceptable limits and still tends to augment the required liquid film for steam generation over the fuel rod lengths downstream (that is immediately above) the spacer. At the same time, the swirl vane structure is placed immediately above the ferrule spacer overlying the so-called subchannel region of the ferrule spacer between the fuel rods.