REMOVABLE TOP NOZZLE OF NUCLEAR-REACTOR FUEL ASSEMBLY (ALTERNATIVES) Russian patent published in 2003 - IPC

FIELD: nuclear power engineering. SUBSTANCE: removable top nozzle is secured on top ends of guide channels 1 in absorbing rods and has hold-down plate 2 and protective guide device 3 with at least one spring 4 in- between. Guide- bushings 6 are passed through holes 7 and 8 in hold-down plate 2 and in protective guide device 3, respectively; they are provided with stops 9 installed, for instance by welding, above hold-down plate 2. Guide bushings 6 are joined through their inner ledges 10 to butt-ends of guide channels 1 and have coupling members 11 in their bottom part made, for instance, in the form of collets engaging, for instance, fillets 12 of guide channels 1. Guide bushings 6 are provided with external projections 13 to mount support members 15. The latter may be made, for instance, in the form of disks or bushings with flanges. Resting on support members 15 are bottom ends of springs 16 which are disposed coaxially to guide bushings 6; hold-down plate 2 rests on these springs. Support members 15 are rigidly coupled with locking members that lock coupling members 11 to form together sleeves 17 whose skirts are engageable with outer surfaces of coupling members 11. Protective guide device 3 may be built of two plates one being support plate and other, bottom plate 18, both rigidly fixed together by means of protective guides 22, or else they can be made of one plate carrying protective guides 22. The latter may be made in the form of perforated conical shell or tilted ribs. Protective guide device 3 rests on stop 24 made of at least one of sleeves 17. Adjustable axial plays are set between radial projections 14 on support members 13 and one of plates of protective guide device 3. Proposed design of top nozzle provides for compensating temperature expansions, as well as radiant and strain elongations of guide channels thereby eliminating distortions of fuel assembly guide channels as a whole due to nonuniform elongation of the latter and of fuel assembly as a whole in the course of operation. EFFECT: enhanced operating reliability of fuel assembly. 3 cl, 7 dwg