Nubbed U-Bend Tube Support

A support bar assembly for supporting the U-bend region of U-tubes in a nuclear steam generator, the U-tubes having a predetermined cross-sectional radius, each U-tube having an intrados, an extrados and a U-tube radius of curvature, the U-tube having the largest radius of curvature defining a maximum bundle radius, the U-tubes being arranged in parallel tube layers, the U-bend region of each tube layer extending from a hot leg to a cold leg and extending radially about a center of curvature from an innermost tube to an outermost tube, each tube layer further defining an in-plane direction and an out-of-plane direction, the assembly comprising:

• a plurality of nubbed support bar arrays, each nubbed bar array associated with an adjacent tube layer and comprising a plurality of first flat elongated bars having inner and outer first flat bar ends, a generally flat elongated bar connected to the inner ends of said plurality of first flat bars and extending across both the hot leg and the cold leg of the associated tube layer, a plurality of nubbed bars, each nubbed bar comprising an elongated body having a nubbed bar outer end, a nubbed bar inner end connected to one of said plurality of first flat bars, first and second flat sides, and a plurality of nubs projecting in the out-of-plane direction from the first side, each nub having a generally rectangular cross-section and a tube contact face generally parallel to one of the intrados and the extrados of a U-tube in the associated U-tube layer;
• first spacer means connected to said first flat bar outer bar ends and nubbed bar outer ends for spacing each nubbed support bar array in the out-of-plane direction;
• and
• a plurality of arcuate tie bars, each tie bar spaced in parallel with the extrados of the outermost tube of the associated tube layer and having an out-of-plane thickness about twice the cross-sectional radius of the U-tubes.