Patent Number: 040627268
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION For a more complete appreciation of the invention, attention is invited to the following description of an illustrative embodiment of the invention, as shown in the attached drawings. In FIG. 1 there is illustrated a nuclear reactor pressure vessel 10 which has a longitudinally disposed cylindrical envelope closed at each end by a convex base and a domed roof. Reactor coolant inlet and outlet nozzles 12 and 14 respectively, protrude from the pressure vessel 10 near the domed roof. These nozzles are generally all disposed in the same plane, that is, transverse to the longitudinal axis of the cylindrical vessel and are separated from each other with an angular displacement. An annular flange 16 formed on the inner surface of the vessel 10 serves as a means for supporting a distribution hoop 18. The hoop 18 has an opening 20, for reactor coolant discharge, which is aligned with the outlet nozzle 14 in the vessel 10. The distribution hoop 18 is extended by means of a skirt 22 and a thermal shield 24 which serve as a hydraulic guide for the incoming fluid coolant entering the annulus 26 formed between the hoop-skirt assembly and the pressure vessel wall from the inlet nozzle 12. Furthermore, the skirt 22 supports the fuel elements in the reactor core (not shown). In operation, the coolant enters the pressure vessel 10 through the inlet nozzle 12 and flows downwardly through the annulus 26, rises through the reactor core (not shown) to the distribution hoop 18, whereupon the heated coolant is discharged from the vessel 10 through the opening 20 and the outlet nozzle 14. As shown in FIG. 2, the outlet nozzle 14 for the vessel 10 is in alignment with the opening 20 in the distribution hoop 18. An outlet nozzle seal 28 in accordance with this invention joins the hoop 18 to the vessel 10 or, more specifically, joins the hoop discharge opening 20 to the reactor pressure vessel outlet nozzle 14. As shown, the seal 28 is disposed within a recess 29 located circumferentially about the opening 20. The seal is comprised of an expansion bellows 30 attached at one end to seal ring 32 and at the other end to a compression ring 34 or the hoop 18. The seal 28 or, more specifically, the expansion bellows 30 is designed such that, in its assembled relationship with respect to the hoop opening 20 and the vessel nozzle 14, it forces the seal ring 32 into sealing engagement with the reactor pressure vessel. Furthermore, this sealing engagement is not dependent on reactor operation or thermal expansion. The seal ring 32 presents a broad surface 33 to engage the pressure vessel and prevent flow leakage therebetween. As shown, the pressure vessel may be cladded with a wear surface 36 to aid in the leak prevention between the seal ring and the vessel and to resist wear due to movement of the hoop-seal assembly with respect to the vessel. The expansion bellows 30 is an impervious hollow cylindrical or annular member having a plurality of flexible convolutions circumferentially disposed about the cylindrically shaped member in order to provide the necessary resiliency so as to prevent the structural coupling of the hoop to the vessel, and also, to provide the necessary force to hold the seal ring 32 in a leak tight relationship about, for example, the vessel nozzle 14. The impervious expansion bellows wall or boundary, moreover, prevents fluid communication across the bellows as is found in other spring seal systems. Furthermore, leakage across the bellows is prevented by seal welding or circumferentially attaching, in a leak-proof manner, the bellows to both the seal ring, at one end, and the compression ring or hoop at the other end. In accordance with this invention, therefore, a leak-proof sealing means is provided for fluid communication from the hoop opening to the outlet nozzle. In the embodiment of the invention shown in FIG. 2 the bellows seal is welded to a compression ring 34 disposed within the recess 29. The compression ring 34 is a cylindrical ring member having an elbow shape cross section. One arm 38 of the compression ring forms an outer protection wall for the expansion bellows spring 30, and the other arm 40 forms a support ring to which the expansion bellows is attached. Further, in this embodiment of the invention, a channel liner 42, connected to the compression ring 34, and, in particular, connected to the ring 40 forms an inner protection wall for the bellows. The compression ring 34 and the channel liner 42 form a cylindrical annular cavity as in the previous spring seal systems. However, in this system, the close tolerance machining of the sealing ring and the cavity are not required, since the bellows wall prevents flow leakage. In addition to forming an inner protection wall which prevents excessive lateral movement of the bellows, the channel liner 42 also serves as a smooth wall flow path from the opening 20 to the nozzle 14 to reduce the flow resistance through the sealing means to the outlet nozzle. In accordance with this invention, flow leakage between the incoming and outgoing coolant in the vicinity of the outlet nozzle 14 is prevented by the seal ring pressure vessel contact established by the self-actuating bellows, and, in addition, fluid communication across the bellows is precluded since the bellows wall provides an impervious cylindrically or annularly shaped boundary across which fluid flow is precluded.