Top Nozzle Having On-Off Type Of Hold-Down Spring In Nuclear Fuel Assembly

A top nozzle having on-off type of hold-down springs for a nuclear fuel assembly, the top nozzle being connected to guide thimbles and an instrumentation tube of the nuclear fuel assembly at the lower end portion thereof and to insertion tubes of a reactor at the upper end portion thereof, thereby fixing the nuclear fuel assembly to the reactor, the top nozzle comprising:

• a hold-down plate having a center hole formed at the center thereof and a plurality of outer holes formed along the outer edge thereof, the plurality of outer holes being spaced apart by a given distance from the center hole and having a given center angle;
• a flow plate having a center hole formed at the center thereof and a plurality of outer holes formed along the outer edge thereof, the plurality of outer holes being spaced apart by a given distance from the center hole thereof and having a given center angle, such that the distance between each outer hole and the center hole of the flow plate is the same as between each outer hole and the center hole of the hold-down plate;
• a plurality of outer guide-tubular sleeves each adapted to be inserted from the upper portion of each outer hole of the hold-down plate, passed through each outer hole of the flow plate, and connected to each guide thimble of the nuclear fuel assembly, each of the outer guide-tubular sleeves having a hold-down plate-locking part disposed at the top end thereof, the hold-down plate-locking part having a larger diameter than the diameter of each outer hole of the hold-down plate;
• a hold-down spring disposed around the outer periphery of each outer guide-tubular sleeve between the hold-down plate and the flow plate, the hold-down spring being supported by the outer guide-tubular sleeve and providing a given elastic force between the hold-down plate and the flow plate;
• a center hold-down plate having a through-hole formed longitudinally therethrough;
• a center guide-tubular sleeve adapted to be inserted from the upper portion of the center hold-down plate and fastened to the center hole of the flow plate;
• and
• a center hold-down spring disposed around the outer periphery of the center guide-tubular sleeve between the center hold-down plate and the flow plate, the center hold-down spring being supported by the center guide-tubular sleeve and providing a given elastic force between the center hold-down plate and the flow plate.