Patent Number: 051046113
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The numeral 10 generally designates the heat exchanger or steam generator which is part of a nuclear steam supply system. A nuclear reactor, generally designated 2 delivers to fluid through a conduit or hot leg 14 from an active core region 16 in the reactor. The fluid enters the reactor through a primary inlet 18 for circulation through core region 16 and out to the hot leg 14. Other details of reactor 12 are well known and not necessary to the present discussion. The steam generator 10 has a generally cylindrical vessel 20 which includes a horizontal tubesheet 22. The vessel 20 has a primary side cavity divided by a divider wall (not shown) into an inlet cavity 24 and outlet cavity 26. The hot leg 14 communicates fluid to the primary side inlet cavity 24. Tubesheet 22 separates the primary side cavity portions 24 and 26 from a secondary side cavity 28. A plurality of U-shaped tubes 30 called a "bundle" are mounted in and extend through the tubesheet 22 in fluid communication, with the primary side cavity, each tube with one end in communication with the primary side inlet cavity 24 and the other with the primary side outlet cavity 26. THe tubes 30 extend into the secondary side cavity 28 to provide a heat exchanging relationship between fluid in the tubes 30 and fluid in the secondary side cavity 28. The secondary side cavity 28 includes an integral "economizer" generally designated by the numeral 32. Economizer 32 is made up of a plurality of baffle plates 34 and passages formed thereby and includes a vertical flow divider plate 36. The economizer 32 preheats incoming feedwater in the outlet side or cold leg side of the tubes 30 in the secondary side cavity 28 on the opposite side of tubesheet 22 from primary outlet cavity portion 26. The secondary side feedwater enters through an upper feedwater inlet 38a and a lower feedwater outlet 38a. An auxiliary feedwater inlet 38c is of no consequence to the invention description. From the feedwater inlets 38a and 38b, fluid is distributed 180.degree. circumferentially around the cold leg side of the tube bundle made of U-shaped tubes 30 and radially inwardly beneath flow distribution baffles 34. Annular gaps in the baffles 34 distribute flow evenly above the baffles around the tubes 30 and upwardly through the bundle in counterflow to primary coolant inside the tubes 30. Feedwater is thus preheated for the first portion of its travel above tubesheet 22. This economizer 32 of the steam generator 10 is separated from the evaporation section in the hot leg side of the tube bundle by a secondary side flow divider plate 36 of with "X" which is attached to the wall of vessel 20 with tongue-and-groove mechanical connections 39 and extends downwardly to the tubesheet 22. The relocation of secondary side handholes 40 to align with the ends of the secondary side flow divider plate 36 is a significant enhancement for field maintenance. It provides improved access for sludge lancing, for annulus inspection and foreign object search and retrieval. The present invention recognizes that with the relocation of the handholes, a problem of access to the full circumference of the tube bundle at that elevation could only be solved by providing a notch 42 at each of the ends of the secondary side divider plate 36. The present invention s a flow blocker and a heat exchanger with a flow blocker to prevent fluid bypass around the end of plate 36 through the notches 42. Each notch 42 is defined by opposed edges 44, which are arcuate and concentric with the adjacent handhole 40. A flow blocker, generally designated 50, is substantially cylindrical, is concentric with the adjacent handhole 40 and notch arcuate surfaces 42 and fits snugly within them. The flow blocker 50 includes a hollow inner cylindrical member 52 having a skirt 54, and end wall 56, with a recess 58, and a centrally apertured transverse flange 60. On the outside of the member 52, telescopically assembled thereto, it a hollow outer cylindrical member 62 into which a spring 64 has been assembled between an outer end wall 66 and the flange 60 of member 52 to bias them in opposite directions. The spring 64 is preloaded by means of a hex-headed rod 68 threaded in end wall 66 of member 62 and seated in recess 58 of member 52. A bolt flange 70 permits attachment of member 62 by means of bolts 72 to a closure plate 74 for handhole 40. The basic components of the flow blocker device 50 consist of commonly used parts such as cylinders springs, threaded rods and bolts. However, the assembled parts are unique in their arrangement for the purpose being used of allowing previously unattainable ease of access to an economizer secondary side for inspection and maintenance.