| 摘要 |
<p>An expandable top nozzle (1) for a nuclear fuel assembly having zircaloy thimble tubes (27) has a cylindrical barrel (3) and an assembly (11) slidable in the barrel (3) which includes a hub (13) and a thin rod ejection plate (19) fixed in spaced relation to the hub (13) by support tubes (15) through which the control rods extend. The support tubes (15) extend through the hub (13) and a spring retainer plate (35) biased against an annular shoulder (9) in the barrel by helical compression springs (45) concentrically mounted with the support tubes (15) in counterbores (41, 43) in the hub (13) and spring retainer plate (35). A centrally located instrument guide tube (57) has a spring loaded plunger (63) which extends through the spring retainer plate (35) and sets the height of an RCCA (55) below the top (5) of the barrel (3) despite expansion and compression of the nozzle (1) with changes in thimble tube length relative to the other internals. The top nozzle (1) is removably attached to a fuel assembly (29) by tubular inserts (99) fixed to the thimble tubes (27) and having collapsed fingers (15) with an annular outward bulge (107) adjacent the free end (103). With the collapsed fingers (15) inserted in the apertures (21) in the rod ejection plate (19), lock tubes (115) are pushed through the support tubes (15) to spread the collapsed fingers (15) of the inserts (99) into engagement with circumferential grooves (113) in the apertures (21).</p> |
