Fuel assembly with a top plate arranged above the upper end surfaces of the fuel rods

A fuel assembly for a boiling water reactor comprising:

• a plurality of fuel rods having vertical center lines;
• at least one bottom plate supporting said fuel rods;
• a vertical fuel channel of rectangular cross-section;
• partition means dividing said fuel channel into four sub-channels, each sub-channel enclosing a bundle of said fuel rods positioned by means of a plurality of spacer devices to constitute a sub-assembly of fuel rods, said spacer devices having a limited freedom of movement in an axially upward direction in relation to said fuel channel;
• and,
• means for limited movement of said fuel rods in an axially upward direction, said movement limited means including a top plate positioned a vertical distance above said fuel rods at room temperature, said top plate comprising:
• a central member arranged in detachable mechanical connection with said partition means,
• a frame disposed with four sides adjacent to corresponding sides of said fuel channel,
• four substantially horizontally directed diagonal bars rigidly connected to corresponding corner portions of said frame at one end and to said central member at the other end, and,
• four substantially horizontally directed cross bars arranged to cross said diagonal bars, said diagonal bars having a mid-portion rigidly connected to a mid-portion of a corresponding cross bar and each of said cross bars having a plurality of horizontally directed first elongated projections each projecting laterally from said cross bar in a direction towards the vertical center line of a corresponding fuel rod,
• said frame having a corner portion positioned vertically above a first group of fuel rods belonging to a said sub-assembly, a second group of fuel rods belonging to the same said sub-assembly being positioned vertically below free end portions of said first elongated projections, and said corner portion and each of said first elongated projections being contactable by corresponding fuel rods upon a sufficiently large vertically upwardly-directed movement of said corresponding fuel rods.