Patent Number: 052767205
Section: description

DETAILED DESCRIPTION OF THE INVENTION Referring initially to FIG. 1, a nuclear BWR system is shown generally at 1. Reactor 10 containing a core, 3, and working fluid, 5, can be seen to be housed within reactor containment 12 which also defines drywell 14. Working fluid 5 generally consists of liquid water which is vaporized upon circulation in a heat transfer relationship with core 3 and passed via a main steam line to a turbine (not shown). Additionally, reactor 10 may contain gaseous noncondensibles, such as inert gases and the like. Also housed within containment 12 is wetwell 16 which is also defined by wall 18. Annular pressure suppression pool 20 is contained within wetwell 16 and connects drywell 14 and wetwell 16 via vent 22. Disposed outside of containment 12 is upper pool 24 which contains a containment condenser, shown generally at 26. Alternatively, containment condenser 26 may be disposed within containment 12. With respect to implementation of the emergency cooling system that is the subject of the instant invention, reactor 10 may be seen to be communicable in a postulated emergency situation with drywell 14 via vent 28. In a postulated LOCA or other emergency situation wherein the main steam line from the reactor is closed or steam flow therethrough is reduced, a gaseous-phase steam and noncondensible mixture will flow from reactor 10 into drywell 14 upon the actuation of vent 28. The direction of the emergency situation flow from reactor 10 into drywell 14 is as represented by arrows 30 and 32. As the gaseous steam and noncondensibles released from reactor vessel 10 may result in a sudden increase in pressure in drywell 14, pressure suppression pool 16 is provided to dampen such transitory phenomena and thereby ensure the structural integrity of containment 12 such that no radioactive materials are released to the environment. When the pressure in drywell 14 exceeds that in containment condenser 26, the gaseous steam and noncondensible mixture will flow from drywell 14 into containment condenser 26 via line 34 as represented by arrow 36. At least a portion of the latent and specific heats of the steam and noncondensible mixture are removed from drywell 14 via transfer to upper pool 26 and exhaustion through vent 38 as represented by arrow 40. The heat transfer from the steam and noncondensible mixture to upper pool 24 via containment condenser 26 results in the condensation of at least a portion of the steam component of the steam and noncondensible mixture passed through containment condenser 26. Condensate is passed from containment condenser 26 to reactor 10 via line 44 as represented by arrow 46. The noncondensed balance of the steam and noncondensible mixture is returned to drywell 14 via outlet 48. Upon return to drywell 14, the noncondensed balance is mixed with the steam and noncondensible mixture passed from reactor 10 to drywell 14. The steam added to drywell 14 via vent 28 from reactor 10 coupled with temperature differentials and condensation in containment condenser 26 will result in the development of a recirculation flow to containment condenser 26 via line 34. With continued reference to FIG. 1, the advantages of the instant invention are revealed upon a closer examination of containment condenser 26. Containment condenser 26 may be seen to comprise a shroud, 50, defining a plenum, 52, in fluid communication with outlet 48 and a plurality of vertical tubes, 54, for passage therethrough of the steam and noncondensible mixture. Tubes 54, which may be linear or helical coils, may be seen to extend in fluid communication with a steam dome, 56, connected to drywell 14 via line 34. At least a portion of the steam component of the steam and noncondensible mixture may condense in tubes 54 and flow therethrough along their inner surfaces. As the condensate is passed from tubes 54 into plenum 52, the shear effect on the noncondensible component of the steam and noncondensible mixture is increased. This increased shear and the higher density of the noncondensibles compared to steam, in effect, drag the noncondensibles out of containment condenser 26. Inasmuch as the heat transfer in containment condenser 26 is governed by the diffusion of steam vapor molecules through a noncondensible layer to a laminar condensate film flowing on the inner surfaces of tubes 54, the presence of noncondensibles in containment condenser 26 may be seen as an impediment to the removal of heat form containment 12. By providing for the removal of noncondensibles from containment condenser 26, the heat transfer between upper pool 24 and containment condenser 26 is enhanced. Moreover, as there is no accumulation of noncondensibles in containment condenser 26, the need for a vent line from containment condenser 26 to suppression pool 20 is eliminated. Instead, the noncondensibles and any noncondensed steam may be vented directly into drywell 14. Consequently, the vacuum breaker check valve between drywell 14 and wetwell 16, and the active cooling systems for wetwell 16, normally associated with emergency cooling systems also become superfluous. Alternatively, as shown at 58, tubes 54 may be oriented at an angle from between about 20.degree. and 40.degree. with respect to vertical. Orientation at such inclination allows condensate to collect on one side of the inner surfaces of tubes 54, making the condensate thinner along the rest of the tube and thereby increasing the heat transfer rate from containment condenser 26 to upper pool 24. Preferably, the length of plenum 52 is about twice the length of tubes 54. Advantageously, flowtrips may be incorporated into tubes 54. Flowtrips may be used to dropletize (i.e., the formation of liquid dropelets) the condensate (shown generally at 60) flowing along the inner surfaces of tubes 54. Dropletizing increases the shear between the condensate and the noncondensibles and thereby enhances the dragging of the noncondensibles out of tubes 54 and containment condenser 26. For vertical tubes 54, flowtrips may be incorporated into the tubes at a preferred spacing of between about 20-50 hydraulic diameters. For slanted tubes 58, flowtrips may be incorporated into the tubes adjacent plenum 52. Referring to FIGS. 2-5, possible embodiments of flowtrips according to the instant invention are shown. Referring to FIG. 2 initially, a flow trip is shown as comprising a cylindrical channel, 62, circumscribed into the inner surface 64 of tube 54 and terminating into generally V-shaped flutes, 62a-c. Condensate 66 flowing down channel 62 of tube 54 is tripped by flutes 62a-c, dropletized, and directed towards annular center 68 of tube 54. Looking to FIG. 3, it may been seen that flutes 62a-c terminating channel 62 may be equilaterally spaced about inner surface 64 of tube 54. Turning to FIG. 4, another embodiment of a flowtrip according to the instant invention is shown as comprising three, equilateral-spaced fins, 70a-c. As may be seen in connection with FIG. 5, fins 70a-c may extend from inner surface 64 of tube 54 towards annular center 68. Fins 70a-c may be acutely angled with respect to inner surface 64 of tube 54. Condensate 66 flowing down inner surface 64 of tube 54 is tripped by fins 70a-c, dropletized, and directed towards annular center 68 of tube 54. As to materials of construction, preferably all components are manufactured from materials appropriate for their use within a nuclear BWR. Further, it will be appreciated that various of the components shown and described herein may be altered or varied in accordance with the conventional wisdom in the field and certainly are included within the present invention, provided that such variations do not materially vary within the spirit and precepts of the present invention as described herein.