Patent Number: 053533194
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT Illustrated schematically in FIG. 1 is an exemplary boiling water reactor (BWR) 10 which includes an annular reactor pressure vessel 12 having a nuclear reactor core 14 submerged in coolant water 16. In this exemplary embodiment, the reactor illustrated is a simplified boiling water reactor (SBWR) which relies on natural recirculation of the water 16 therein instead of driven pumps for circulating the water therein. Accordingly, a conventional annular chimney 18 extends upwardly from the core 14 and includes a plurality of vertical, spaced apart partitions (not shown) for channeling upwardly the water heated by the core 14 to generate steam 16a. Disposed at the top of the chimney 18 are a plurality of conventional steam separators 20 having conventional tubular standpipes disposed in flow communication with the chimney 18. A portion of the steam 16a is separated from the water vapor and is further channeled upwardly into a conventional steam dryer 22 which removes further water vapor therefrom prior to discharging the steam 16a from the vessel 10 through a conventional outlet nozzle 24. To replenish the water 16 lost from the vessel 12 due to the steam 16a discharged therefrom, a feedwater sparger assembly 26 which is removable in accordance with the present invention is provided at the top of the chimney 18 around the inner circumference of the pressure vessel 12. The assembly 26 includes one or more conventional feedwater nozzles 28 through the vessel 12 which provide feedwater 16b into the vessel 12 from a suitable external source. The core 14 and the chimney 18 are spaced radially inwardly from the inner circumference of the vessel 12 to define an annular downcomer 30 therebetween in which flows downwardly by natural circulation the relatively cold feedwater 16b mixed with the water 16 in the vessel 12. The core 14 heats the reactor water 16 which decreases its density and causes it to rise upwardly through the chimney 18, while the relatively cool and denser water in the downcomer 30 flows downwardly to the bottom of the pressure vessel 12, wherein it turns upwardly and enters the core 14. Accordingly, a recirculation flowpath is created by the water and steam which flows upwardly through the chimney 18 and then laterally into the top of the downcomer 30 wherein the heated reactor water 16 is mixed with the cooler feedwater 16b and flows downwardly in the downcomer 30. During a maintenance outage, the top head of the pressure vessel 12 is conventionally removed, followed in turn by the steam dryer 22 and the steam separators 20 if required. And, in order to get access to the downcomer 30 below the sparger assembly 26 for inspection and maintenance in the downcomer 30, the sparger assembly 26 is removable in accordance with the present invention. Referring to FIG. 2, the assembly 26 may include one or more arcuate feedwater spargers 32. The sparger 32 includes an arcuate, horizontal header pipe 34 having a plurality of circumferentially spaced injector nozzles 36 disposed in flow communication therewith at the top thereof for injecting the feedwater 16b into the downcomer 30. Although the sparger 32 and the header pipe 34 may be full 360.degree. rings, in the exemplary embodiment illustrated in FIGS. 1 and 2, four identical circumferentially spaced apart arcuate header pipes 34 are used which collectively extend about 270.degree. of the full circumference of the downcomer 30. As shown with more particularity in FIGS. 3 and 4, the sparger 32 includes a conventional reducing or coupling pipe tee 38 disposed at an intermediate portion of the header pipe 34, with the trunk of the tee 38 defining a vertical inlet pipe 40 for the sparger 32 for channeling the feedwater 16b through the two branches of the tee 38 circumferentially in opposite directions into the header pipe 34 for discharge from the injector nozzles 36. As illustrated in cross-section in FIG. 5, the inlet pipe 40 has an annular distal end 40a and an intermediate portion 40b spaced longitudinally upwardly therefrom. Referring to both FIGS. 3 and 5, a supply pipe 42 includes a 90.degree. elbow 42a and an integral cylindrical thermal sleeve 42b extending horizontally from the elbow 42a in conventional flow communication with the inside of the feedwater nozzle 28 for receiving therefrom the feedwater 16b. The supply pipe elbow 42a has an upwardly facing outlet end 42c as illustrated in FIG. 5 for receiving therein the inlet pipe distal end 40a in flow communication therewith for channeling the feedwater 16b from the supply pipe 42 to the inlet pipe 40 to feed the sparger 32. The supply pipe outlet end 42c includes an annular, radially outwardly extending retention flange 44 which mates with a tubular sleeve or coupling 46 joined to the inlet pipe 40. The coupling 46 is shown in cross-section in FIG. 5 and in perspective in FIG. 6 and includes an annular band 46a at a proximal end thereof fixedly joined coaxially with the intermediate portion 40b of the sparger inlet pipe 40 by a conventional weld 48. The coupling 46 also includes a plurality of circumferentially spaced, elongate fingers 46b extending longitudinally and vertically from the band 46a and integral therewith. The fingers 46b are removably hooked or joined to the retention flange 44 for maintaining the sparger inlet pipe 40 in flow communication with the supply pipe 42, while allowing relatively easy disassembly thereof during the maintenance outage. As illustrated in FIG. 5, the retention flange 44 is preferably cylindrical and defines with an outer surface of the supply pipe 42 an annular, horizontal outer seat or ledge 44a for capturing the coupling fingers 46b thereon. The retention flange 44 also defines with an inner surface of the supply pipe 42 an annular, horizontal inner seat or ledge 44b for receiving therein the inlet pipe distal end 40a in a male and female coupling arrangement. An elastic or flexible annular seal 50 rests on the inner ledge 44b and is disposed between the inlet pipe distal end 40a and the inner ledge 44b and is sized for being elastically compressed therebetween upon engagement of the fingers 46b and the retention flange 44. In the exemplary embodiment illustrated in FIGS. 5 and 7, the seal 50 is a conventional Belleville seal made from a suitable metal which provides both sealing and elastic compression capability. Other types of suitable seals such as metallic O-rings or resilient metal seals may also be used. As shown in FIGS. 6 and 7, each of the fingers 46b includes an elongate, flexible beam 52 extending integrally from the band 46a and spaced parallel to adjacent ones of the beams 52. Disposed at a distal end of each of the beams 52 is a hook 54 defined by a flat seat 54a disposed parallel to the outer ledge 44a as illustrated in FIG. 5 for retention thereon, and a ramp 54b inclined radially outwardly from the seat 54a and integral therewith. As illustrated with more particularity in FIG. 7, the ramp 54b is configured for engagement with the supply pipe outlet end 42c by having an initially smaller diameter relative thereto to displace radially outwardly or elastically expand the fingers 46b over the retention flange 44 upon installation and translation downwardly of the inlet pipe 40 into the supply pipe 42 until the hooks 54 contract or snap radially inwardly and latch the outer ledge 44a as illustrated in FIG. 5. The lengths of the fingers 46b are selected to ensure that the seal 50 is slightly compressed between the inlet pipe distal end 40a and the inner ledge 44b upon engagement of the hooks 54 with the outer ledge 44a. This ensures an effective seal for reducing or preventing leakage of the feedwater 16b through the joint between the inlet pipe 40 and the supply pipe 42 as well as provide a vibration-resistant joint. Since the supply pipe outlet end 42c faces upwardly, and the sparger inlet pipe 40 extends vertically with the distal end 40a thereof facing downwardly toward the supply pipe outlet 42c, the sparger 32 may be readily installed by simple downward movement and insertion of the sparger inlet pipe 40 into the supply pipe outlet end 42c, with engagement of the fingers 46b with the retention flange 44 maintaining the assembly together. In order to allow relatively easy disassembly of the sparger 32 from the supply pipe 42, an annular release collar 56 as illustrated in FIGS. 5 and 7 is loosely or slidably disposed around the supply pipe 42 adjacent to and below the retention flange 44 and the fingers 46b. The release collar 56 includes a frustoconical, or simply conical cam surface 56a for selectively engaging the fingers 46b upon longitudinal upward translation thereof to displace the fingers 46b radially outwardly from the retention flange 44 for disengagement therewith as illustrated in phantom line in FIG. 7. As illustrated in FIG. 7, the hook ramp 54b is also configured for engagement with the release collar cam surface 56a upon translation of the cam surface 56a upwardly against the several ramps 54b to expand radially outwardly the fingers 46b to disengage the hooks 54 from the outer ledge 44a for removing the inlet pipe 40 and the sparger 32 from the supply pipe 42. As shown in FIGS. 5 and 7, an annular support collar 58 is fixedly joined to the supply pipe 42, on the elbow 42a, by welding for example, and below the release collar 56 for supporting the release collar 56 and maintaining it in ready position. Accordingly, when desired, the release collar 56 may be manually translated upwardly, using suitable pneumatic jacks for example, to spread apart the fingers 46b and release the coupling 46 from the retention flange 44 to remove the sparger 32. As illustrated in FIG. 5, the retention flange 44 is preferably sized to fit completely within the coupling 46 axially between the band 46a and the hooks 54 and radially inwardly of the beams 52. In this way, a compact joint is created which does not reduce the inner diameter or flow area between the supply pipe 42 and the inlet pipe 40. The various components of the sparger assembly 26 are made of conventional metals for the nuclear environment. However, in a preferred embodiment of the present invention, the coupling 46 preferably is made of a material such as conventional Inconel X-750, which has a lower coefficient of thermal expansion than the materials of the supply pipe 42 and the inlet pipe 40 cooperating therewith so that differential thermal expansion therebetween upon heating thereof in the reactor environment will additionally compress the seal 50 for increasing its effectiveness. In this way, the fingers 46b will expand less than the supply pipe 42 and the inlet pipe 40 between the coupling band 46a and the hooks 54 to tighten the seal joint during operation upon heating thereof. Although the coupling 46 is joined to the inlet pipe 40 and the retention flange 44 is joined to the supply pipe 42 in the preferred embodiment, they may be interchanged in an alternate embodiment as shown in FIG. 8. In this embodiment, the retention flange 44A is integral with the distal end of the inlet pipe 40, the coupling 46A is joined to the supply pipe 42 by suitable pins 60, and the release collar 56A surrounds the inlet pipe 40. The joint still functions the same in this embodiment. While there have been described herein what are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein, and it is, therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention. Accordingly, what is desired to be secured by Letters Patent of the United States is the invention as defined and differentiated in the following claims: