Patent Number: 046719237
Section: claims

1. In a nuclear reactor having a pressure vessel, a core barrel with an upper outwardly extending flange, an inner barrel with an upper outwardly extending flange, an annular holddown spring positioned between said core barrel flange and said inner barrel flange, said barrels and said spring being installed in said pressure vessel, during normal operation, with said inner barrel flange disposed above said core barrel flange and said holddown spring interposed between said core barrel flange and said inner barrel flange; a holddown spring retention assembly comprising a plurality of assembly units disposed around the periphery of said holddown spring, with each said unit comprising: lift lug means secured to the outer periphery of said spring and having at least one outwardly radially projecting portion; and hanger means secured to said inner barrel flange and having a lower portion suspended below said inner barrel flange and below said radially projecting portion of said lift lug means, said lower portion being arranged to support said radially projecting portion during lifting of said inner barrel upwardly away from said core barrel so that said spring is lifted together with said inner barrel. 2. An assembly as defined in claim 1 wherein said assembly units are equally spaced about the periphery of the holddown spring. 3. Apparatus as defined in claim 2 wherein said lift lug means have two said outwardly radially projecting portions, and a support plate portion secured directly to the spring and having an outer surface extending parallel to the spring periphery, and said radially projecting portions extend from said radial outer surface and are spaced apart in the direction of the circumference of the spring. 4. Apparatus as defined in claim 3 wherein said hanger means are composed of a first part in the form of an "I", with said lower portion constituting a lower horizontal portion of the "I", said first part further including an upper horizontal portion and a vertical web portion connecting said horizontal portions together, said hanger means being secured to the inner barrel flange via said upper horizontal portion so that said vertical web portion passes between said radially projecting portions of said lift lug means. 5. Apparatus as defined in claim 4 wherein said radially projecting portions of said lift lug means are dimensioned to be out of contact with said lower horizontal portion of said hanger means in the assembled state of the reactor. 6. Apparatus as defined in claim 5 wherein said hanger means are further composed of a second part in the form of a reinforcing plate integral with said lower horizontal portion and said vertical web portion of said first part at the side of said hanger means remote from the spring. 7. Apparatus as defined in claim 6 wherein said radially projecting portions of said lift lug means are dimensioned to cooperate with said second part of said hanger means for maintaining accurate radial positioning of the spring relative to the inner barrel flange. 8. Apparatus as defined in claim 7 wherein said hanger means are further composed of a third part in the form of two shoulder portions each enclosed by, and integral with, said vertical web portion, said second part of said hanger means, each said shoulder portion enclosed by, and integral with, said vertical web portion, said lower horizontal portion and said second part of said hanger means, each said shoulder portion being disposed to a respective side of said vertical web portion and being dimensioned to cooperate with said outwardly radially projecting portions of said lift lug means in order to maintain accurate circumferential positioning of the spring relative to the inner barrel flange. 9. Apparatus as defined in claim 2 wherein said hanger means have the general form of a "C", with said lower portion constituting a lower horizontal portion of the "C", said hanger means further including an upper horizontal portion and a vertical web portion connecting said horizontal portions together, said hanger means being secured to the inner barrel flange via said upper horizontal portion. 10. Apparatus as defined in claim 9 wherein said lift lug means have a single outwardly radially projecting portion. 11. Apparatus as defined in claim 10 wherein said upper and lower horizontal portions of said hanger means are each joined at a respective end to said vertical web portion and both extend in the same direction along the circumference of the spring from said vertical web portion. 12. Apparatus as defined in claim 11 wherein said radially outwardly projecting portion of said lift lug means is dimensioned to cooperate with said vertical web portion of said hanger means for circumferentially positioning the spring relative to the inner barrel flange. 13. Apparatus as defined in claim 10 wherein said upper and lower horizontal portions of said hanger means are each joined at a respective end to said vertical web portion and both extend radially inwardly toward the spring from said vertical web portion. 14. Apparatus as defined in claim 13 wherein said radially outwardly projecting portion of said lift lug means is dimensioned to cooperate with said vertical web portion of said hanger means for radially positioning the spring relative to the inner barrel flange. 15. In a nuclear reactor having a pressure vessel, a core barrel with an upper outwardly extending flange, an inner barrel with an upper outwardly extending flange, and an annular holddown spring, and wherein, in the assembled state of the reactor, said barrels and said spring are installed in said pressure vessel with said inner barrel flange above said core barrel flange and with said spring interposed between said flanges; a retention assembly comprising a plurality of assembly units disposed at equal spacings around the periphery of the spring, and with each said unit comprising: a lift lug secured to the outer periphery of the spring and composed of a support plate portion secured directly to the spring and having an outer surface extending parallel to the spring periphery, and two outwardly radially projecting portions extending from said outer surfacer and spaced apart in the direction of the circumference of the spring; and  a hanger composed of a first part in the form of an "I" including upper and lower horizontal portions and a vertical web portion connecting said horizontal portions together, said hanger being secured to the inner barrel flange via said upper horizontal portion so that said lower horizontal portion is suspended below the inner barrel flange and below said radially projecting portions of said lift lug and said vertical web portion passes between said radially projecting portions, said lower horizontal portion being arranged to support said radially projecting portions during lifting of the inner barrel away from the core barrel so that the spring is lifted together with the inner barrel, said radially projecting portions being dimensioned to be out of contact with said lower horizontal portion in the assembled state of the reactor, said hanger further being composed of a second part in the form of a plate integral with said lower horizontal portion and said vertical web portion at the side of said hanger remote from the spring for reinforcing said hanger, and said radially projecting portion being dimensioned to cooperate with said second part of said hanger for maintaining accurate radial positioning of the spring relative to the inner barrel flange.  a lift lug secured to said outer peripheral surface of said spring and composed of a support plate portion secured directly to said spring and having an outer surface extending parallel to said spring outer peripheral surface, and two outwardly radially projecting portions extending from said outer surface and spaced apart in the direction of the circumference of said spring; and  a hanger composed of a first part in the form of an "I" including upper and lower horizontal portions and a vertical web portion connecting said horizontal portions together, said upper horizontal portion being disposed in said horizontal portion of a respective groove in said inner barrel flange for securing said hanger to said inner barrel flange and said vertical web portion lying in said vertical portion of said respective groove, so that said lower horizontal portion is suspended below said inner barrel flange and below said radially projecting portions of said lift lug and said vertical web portion passes between said radially projecting portions, said lower horizontal portion being arranged to support said radially projecting portions during lifting of said inner barrel away from said core barrel so that said spring is lifted together with said inner barrel, said radially projecting portions being dimensioned to be out of contact with said lower horizontal portion in the assembled state of said reactor, said hanger further being composed of a second part in the form of a reinforcing plate integral with said lower horizontal portion and said vertical web portion at the side of said hanger remote from said spring, and said radially projecting portions being dimensioned to cooperate with said second part of said hanger for maintaining accurate radial positioning of said spring relative to said inner barrel flange. 16. A holddown spring retention assembly in combination with nuclear reactor, said reactor comprising a pressure vessel, a core barrel having an upper outwardly extending flange, an inner barrel having an upper outwardly extending flange and an annular holddown spring having an outer peripheral surface, in the assembled state of said reactor, said barrels and said spring being installed in said pressure vessel with said inner barrel flange above said core barrel flange and said spring interposed between said flanges, and said inner barrel flange being provided with a plurality of grooves uniformly spaced about the circumference of said inner barrel flange, each groove extending radially inwardly from the periphery of said inner barrel flange and having a horizontal portion extending to the upper surface of said inner barrel flange and a vertical portion extending from said horizontal portion to the lower surface of said inner barrel flange, and said retention assembly comprising a plurality of assembly units uniformly spaced about the circumference of said spring, and each said unit comprising: