Patent Number: 
Section: description

FIG. 1 is a schematic diagram of a nuclear reactor 10 in accordance with an embodiment of the present invention. Reactor 10 includes a reactor pressure vessel 12 located inside a containment vessel 14. A reactor core 16 is located inside reactor pressure vessel 12. Containment vessel 14 includes a drywell 18, which houses reactor pressure vessel 12, and an enclosed wetwell 20. A suppression pool 22 is located inside wetwell 20. A cooling condenser pool of water 24 is located outside containment vessel 14. A plurality (two shown) of containment cooling condensers 26 are submerged in cooling pool 24. Condenser 26 includes an inlet line 28 in fluid communication with drywell 18. Steam and noncondesible gases flow from drywell 18 through inlet line 28 to an upper drum 30 of condenser 26 and then into a condensing section 32 where the steam is condensed and collected in a lower drum 34. A condensate drain line 36 extends from lower drum 34 of condenser 26 to a condensate drain tank 38. An injection line 39 extends from condensate drain tank 38 to pressure vessel 12 and condensate drains to pressure vessel 12 through injection line 39. Drain line 36 includes a U-pipe loop seal or water trap 40 to restrict the backflow of steam and noncondensible gases from flowing backward through condensate drain line 36 and into condenser 26. A noncondensible gas vent line 42 extends from lower drum 34 to wetwell 20. An outlet end 44 of vent line 42 is submerged in suppression pool 22. A drywell gas recirculation subsystem 46 prevents the buildup of noncondesible gases in wetwell 20. Drywell gas recirculation subsystem 46 includes a suction line 48 connected to and in fluid communication with noncondensible gas vent line 42 at a location downstream of condenser 26 and above outlet end 44 of vent line 42, one or more blowers 50 (one shown) connected to suction line 48, at least one valve 52 (two shown), and a discharge line 54. Discharge line 54 includes a first end 56 and a second end 58. First end 56 of discharge line 54 is connected to blower 50 and second end 58 is open to drywell 18. Valves 52 can be any suitable valves, for example, pyrotechic-type squib valves. Blower 50 circulates the drywell atmosphere through condensers 26 by forced circulation. Particularly, the noncondensible gases circulate from condensing section 32 of condenser 26 through vent line 42 through suction line 48 and are returned to drywell 18, instead of discharging in wetwell 20. Drywell gas recirculation subsystem 46, once actuated, remains as a closed loop extension of containment vessel 14. Locked open maintenance block valves 60 are located outboard of containment vessel 14 on suction line 48 and discharge line 54. Block valves 60 permit servicing of any component of subsystem 46 without the need for drywell entry. FIG. 2 is a schematic diagram of another embodiment of a containment cooling system 62 shown in FIG. 1. In this embodiment drywell gas recirculation subsystem 46 is located entirely inside containment vessel 14. As described above, containment cooling system 62 includes containment vessel 14 having a drywell 18 and a wetwell 20. Cooling condenser 26 is submerged in cooling pool 24 located outside containment 14. Condenser 26 includes inlet line 28 in fluid communication with drywell 18 and connected to upper drum 30, condensing section 32, and lower drum 34. Noncondensible gas vent line 42 extends from lower drum 34 of condenser 26 to wetwell 20 with outlet end 44 of vent line 42 submerged in suppression pool 22. Condensate drain line 36 extends from lower drum 34 of condenser 26 to condensate drain tank 38, and includes U-pipe loop seal 40. The height of loop seal 40 is defined as HLOOP. Condensate drain tank 38 includes a pool of water 64, and condensate drain line 36 enters condensate drain tank 38 above the surface of pool 64. Drywell gas recirculation subsystem 46 includes suction line 48 connected to and in fluid communication with noncondensible gas vent line 42, blower 50 connected to suction line 48, squib valve 52, and discharge line 54. FIG. 3 is a schematic diagram of a straight pipe loop seal 66 of containment cooling system 62 in accordance with another embodiment of the present invention. In this embodiment, condensate drain line 36 is vertically submerged into drain tank 38 a distance HSUB below the surface of drain tank pool of water 64. The advantage of this arrangement is that the static head for the flow passing through drain line 36 is biased depending on the flow direction. Defining the cross-sectional area of drain line 36 and drain tank 38 as APIPE and ATANK respectively, and a forward flow direction as the flow of condensate and noncondensible gases from condenser 26 through drain line 36, into drain tank 38, and to drywell 18. For forward flow, the pressure inside drain line 36 needs to be greater than the pressure in drywell 18 to push down the water level inside drain line 36 to an outlet end 68 of drain line 36. The water level in drain tank 38 rises due to the incoming water volume from drain line 36. The submergence of drain line outlet end 68 becomes HSUB*(1+APIPE/(ATANKxe2x88x92APIPE)). This is the static head difference between the pressure in drain line 36 and the pressure in drywell 18 for the forward flow to occur. For an embodiment with (APIPE/ATANK) greater than  greater than 1, or for an embodiment where the water level in drain tank 38 is controlled by the location of injection line 39, the static head for the forward flow is ≅HSUB. The backward flow direction is defined as the flow from drywell 18, through drain tank 38 into drain line 36. For backward flow to occur, the pressure in drywell 18 has to be sufficiently greater than the pressure in drain line 36 to push down the water level inside tank 38 to drain line exit elevation. In this situation, the water level inside drain line 36 rises due to incoming water volume from drain tank 38. The length of the water column inside drain line 36 is HSUB*ATANK/APIPE. This is the static head difference between the pressure in drywell 18 and the pressure in drain line 36 for backward flow to occur. By using the appropriate area ratio between drain tank 38 and drain line 36, the backward flow static head in straight pipe loop seal 66 (shown in FIG. 3) is HSUB*ATANK/APIPE, which can be greater than that in U-pipe loop seal 40 (shown in FIG. 2) of 2*HLOOP. For the same area ratio, the forward flow static head in straight pipe loop seal 66 is HSUB, which can be a fraction of HLOOP in U-pipe loop seal 40 due to the area multiplication factor. Therefore, the advantage of straight pipe loop seal 66 shown in FIG. 3 is a lower static head for forward flow. FIG. 4 is a schematic diagram a portion of containment cooling system 62 that includes a blower 70 in condenser drain line 36 in accordance with another embodiment of the present invention. Blower 70 enhances the flow through condenser 26 and recirculates noncondensible gases back to drywell 18 through condensate drain tank 38. Blower 70 is connected to condensate drain line 36 at a location between lower drum 34 of condenser 26 (shown in FIG. 2) and drain tank pool of water 64. As explained above, the head requirement of blower 70 is less in a drain line 36 that is connected to drain tank 38 with a straight pipe loop seal 66 than a drain line 36 that is connected to drain tank 38 with a U-tube loop seal 40. In alternate embodiments, containment system 62 includes more than one blower 70 in drain line 36. FIG. 5 is a schematic diagram of a portion of containment cooling system 62 that includes three condensate drain lines 36 extending into drain tank 38 in accordance with another embodiment of the present invention. Each condensate drain line 36 includes a blower 70. FIG. 6 is a schematic diagram of a portion of containment cooling system 62 that includes a jet pump 72 in condensate drain line 36 in accordance with another embodiment of the present invention. Jet pump 72 includes a suction line 74, a pump 76 coupled to and in flow communication with suction line 74, a discharge line 78 extending from pump 76 to a jet pump nozzle 80 located inside drain line 36, and a venturi 82 located in drain line 36. Jet pump nozzle 80 is positioned upstream from venturi 82 in drain line 36. An end 84 of suction line 74 is positioned in condensate drain tank pool of water 64. Jet pump suction line 74 takes water from drain tank 38 which is circulated by pump 76 through discharge line 78, and injected into venturi 82 in drain line 36 via jet pump nozzle 80 at high velocity. Low pressure is created in venturi 82 by the high jet velocity of the water. The mixture of condensate and noncondensible gases are drawn through venturi 82 and discharged into drain tank 38. The condensate is collected in drain tank 38 and the noncondensible gases are discharged back to drywell 18. As explained above, the head requirement of jet pump 72 is less in a drain line 36 that is connected to drain tank 38 with a straight pipe loop seal 66 than a drain line 36 that is connected to drain tank 38 with a U-tube loop seal 40. In alternate embodiments, drain line 36 includes more than one jet pump 72. FIG. 7 is a schematic diagram a portion of containment cooling system 62 that includes three condensate drain lines 36 extending into drain tank 38 in accordance with another embodiment of the present invention. Each condensate drain line 36 includes a jet pump 72. FIG. 8 is a schematic diagram a portion of a containment cooling system 62 showing three condensate drain lines 36 extending into drain tank 38. A jet pump 72 is located in one drain line 36, a blower 70 is located in a second drain line 36, and a gravity driven suction pump 86 is located in a third drain line 36 in accordance with another embodiment of the present invention. Gravity driven suction pump 86 includes a suction line 88 extending from lower drum 34 of condenser 26 into venturi section 82 of drain line 36. Gravity driven suction pumps are described in greater detail in U.S. Pat. No. 6,097,778. The above described nuclear reactor containment cooling system 62 enhances flow through condenser 26 as compared to known passive containment cooling systems. Also, the above described containment cooling system 62 effectively redistributes the noncondensible gases between drywell 18 and wetwell 20. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.