EP4634575A1 - Safety condenser and nuclear reactor containing the same - Google Patents

Safety condenser and nuclear reactor containing the same

Info

Publication number
EP4634575A1
EP4634575A1 EP22822616.3A EP22822616A EP4634575A1 EP 4634575 A1 EP4634575 A1 EP 4634575A1 EP 22822616 A EP22822616 A EP 22822616A EP 4634575 A1 EP4634575 A1 EP 4634575A1
Authority
EP
European Patent Office
Prior art keywords
heat exchanger
generating component
steam
safety condenser
steam generating
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22822616.3A
Other languages
German (de)
French (fr)
Inventor
Simon SCHOLLENBERGER
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Framatome GmbH
Original Assignee
Framatome GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Framatome GmbH filed Critical Framatome GmbH
Publication of EP4634575A1 publication Critical patent/EP4634575A1/en
Pending legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B37/00—Component parts or details of steam boilers
    • F22B37/002—Component parts or details of steam boilers specially adapted for nuclear steam generators, e.g. maintenance, repairing or inspecting equipment not otherwise provided for
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28B—STEAM OR VAPOUR CONDENSERS
    • F28B1/00—Condensers in which the steam or vapour is separate from the cooling medium by walls, e.g. surface condenser
    • F28B1/02—Condensers in which the steam or vapour is separate from the cooling medium by walls, e.g. surface condenser using water or other liquid as the cooling medium
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D1/00—Heat-exchange apparatus having stationary conduit assemblies for one heat-exchange medium only, the media being in contact with different sides of the conduit wall, in which the other heat-exchange medium is a large body of fluid, e.g. domestic or motor car radiators
    • F28D1/02—Heat-exchange apparatus having stationary conduit assemblies for one heat-exchange medium only, the media being in contact with different sides of the conduit wall, in which the other heat-exchange medium is a large body of fluid, e.g. domestic or motor car radiators with heat-exchange conduits immersed in the body of fluid
    • F28D1/0206—Heat exchangers immersed in a large body of liquid
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C15/00—Cooling arrangements within the pressure vessel containing the core; Selection of specific coolants
    • G21C15/18—Emergency cooling arrangements; Removing shut-down heat
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21D—NUCLEAR POWER PLANT
    • G21D1/00—Details of nuclear power plant
    • G21D1/02—Arrangements of auxiliary equipment
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D21/00—Heat-exchange apparatus not covered by any of the groups F28D1/00 - F28D20/00
    • F28D2021/0019—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for
    • F28D2021/0054—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for for nuclear applications

Definitions

  • the present invention concerns a safety condenser intended to be connected to a steam generator in a nuclear reactor.
  • the present invention relates to a nuclear reactor.
  • US 4,765,946 discloses a safety condenser intended to be connected to a steam generator in a nuclear reactor, comprising a heat exchanger arranged in a pool containing a cooling fluid, the heat exchanger comprising a bundle of parallel heat exchanger tubes.
  • WO 93/04481 discloses a safety condenser intended to be connected to a steam generator in a nuclear reactor, comprising a heat exchanger arranged in a pool containing a cooling fluid, the heat exchanger comprising a bundle of heat exchanger tubes.
  • WO 93/04480 discloses a safety condenser intended to be connected to a steam generator in a nuclear reactor, comprising a heat exchanger comprising a bundle of heat exchanger tubes.
  • Object of the present invention is to provide a safety condenser for a steam generator, which has a heat exchange capacity, which can be easily adjusted depending on the needs.
  • a safety condenser intended to be connected to a steam generating component in a water-cooled nuclear reactor comprising:
  • a heat exchanger partially arranged in a pool containing a cooling fluid, the heat exchanger comprising a bundle of parallel heat exchanger tubes, the heat exchanger tubes extending in a vertical direction between a lower tube sheet and a upper tube sheet, each heat exchanger tube being intended for receiving a downward flow of steam from the steam generating component, the heat exchanger comprising an inlet, intended for receiving steam generated in the steam generating component, the heat exchanger being configured for cooling this steam through heat exchange with the cooling fluid contained in the pool to produce condensate and an outlet, configured for returning the condensate to the steam generating component; and
  • a cooling capacity regulator configured for controlling the cooling capacity of the safety condenser by adjusting the height of the condensate in the heat exchanger tubes
  • the heat exchanger further comprises a lower end dome connected to the lower tube sheet and comprising the outlet intended to be connected to the steam generating component and upper end dome connected to the upper tube sheet and comprising the inlet intended to be connected to an outlet pipe of the steam generating component, the lower end dome and the upper end dome being located outside of the pool.
  • the pool is arranged in a housing, the housing having a first opening in a covering and a second opening in the bottom, the first and second openings are vertically aligned to each other, wherein the heat exchanger extends through the first and second openings.
  • the lower tube sheet is connected to a support frame having a larger outer diameter than the diameter of the second opening, wherein in particular the support frame has a smaller outer diameter than the diameter of the first opening;
  • the safety condenser further comprising a sealing arrangement between the upper end dome and the housing, wherein the sealing arrangement comprises an axial compensator enabling an axial movement along the longitudinal axis of the heat exchanger of the upper end of the heat exchanger with respect to the housing;
  • a shielding baffle is arranged spaced apart from the heat exchanger tubes and/or the axial compensator
  • the safety condenser further comprising a sealing support, wherein the outer diameter of the sealing support has a larger diameter than the first opening, wherein the axial compensator is fixed to the sealing support;
  • the first opening has a step shaped inner border and the sealing support has a step shaped outer border being at least partially complementary to the steps of the inner border of the first opening;
  • the cooling capacity regulator comprises at least one valve, in particular a plurality of valves being connected in parallel, wherein the at least one valve is arranged in a return line between the outlet and the steam generating component;
  • the bundle of heat exchanger tubes is at least partially surrounded by a flow skirt, wherein in particular the flow skirt covers at least 50 percent of the length of the bundle of heat exchanger tubes;
  • a water-cooled nuclear reactor comprising a safety condenser according to an embodiment disclosed herein.
  • the steam generating component is a steam generator of a pressurized water reactor or a reactor pressure vessel of a boiling water reactor.
  • the water-cooled nuclear reactor further comprising a steam generating component, wherein the inlet of the heat exchanger is connected to an outlet pipe of the steam generating component and the outlet of the heat exchanger is connected to the steam generating component.
  • the water-cooled nuclear reactor further comprising a passive pressure pulse transmitter adapted to emit a hydraulic pulse towards at least one of the return line valves in case the water level in the steam generating component falls below a predetermined level.
  • the nuclear reactor utilizes light water as primary cooling medium.
  • Fig. 1 shows schematically a nuclear power plant with a pressurized water reactor
  • Fig. 2 shows schematically a safety condenser according to an embodiment
  • Fig. 3 shows schematically the connection of the safety condenser to the steam generator for a pressurized water reactor
  • Fig. 4 shows schematically the structures and function of the passive pressure pulse transmitter (PPPT).
  • Fig. 5 shows schematically the connection of the safety condenser to the reactor pressure vessel of a boiling water reactor.
  • FIG. 1 provides a simplified schematic overview of a nuclear power plant 1 with a nuclear reactor in form of a pressurized water reactor (PWR) 3.
  • the PWR 3 comprises a reactor core 5 having a reactor pressure vessel (RPV) 7.
  • a primary cooling medium for example water
  • the primary cooling circuit includes one or more steam generators 14, in which the heat of the primary cooling medium is transferred to a secondary cooling medium circulating in a secondary cooling circuit 16, thereby evaporating the secondary cooling medium.
  • the primary cooling medium is then conducted again into the reactor core 5 by the RCP 12.
  • the secondary cooling circuit 16 is for a water-steam cycle.
  • the steam is guided to one or more turbines 18, which drives respectively a generator 20 to produce electricity.
  • the steam is further guided from the turbine 18 to a condenser 22, where it is cooled down and condensed. Then it is pumped by a second pump 24 back to the one or more steam generator 14, in particular via a return line.
  • the second pump 24 is also called condensate pump.
  • At least one safety condenser 25 comprising a heat exchanger 26, in particular a straight-tube heat exchanger 26.
  • the safety condenser 25 described hereafter is connected to the steam-generating component in a water-cooled nuclear reactor. In case of a pressurized water reactor the safety condenser 25 is connected to the steam generator 14.
  • the heat exchanger 26 is connected at its first end to an outlet 28 of at least one steam generator 14 in the secondary circuit 16 via a charge line and at its second end to a downcomer section 29 of the same steam generator.
  • the second end of the steam generator 14 is connected to an upper end of the downcomer section 29, in particular to allow mixing with secondary side feed water to reduce thermal stress for the steam generator tube sheet or return line connection nozzles.
  • the second end is connected to a return line of the secondary cooling circuit 16, wherein the return line returns the condensed steam to the steam generator 14.
  • the first end is the upper end in the drawings and the second end the lower end in the drawings.
  • Each safety condenser 25 with the heat exchanger 26 is provided to condense the steam produced in the steam generating component, in case of a pressurized water reactor the steam generator 14, for the purpose of removing heat from the decay circuit in case of a failure of feed water supply to the steam generating component.
  • the details will be described with respect to a single safety condenser 26. As indicated above, more than one, in particular 2, 3, 4 or more safety condenser 26 may be used.
  • the safety condenser 26 provides an additional heat sink for the reactor coolant, for example the secondary cooling medium.
  • the safety condenser and its pool provide an additional heat sink for the decay heat still generated by the reactor core 5 after shut-down, thus avoiding a continuous level drop in either the steam generator 14 of a PWR 3 or the reactor pressure vessel 7’ of a boiling water reactor explained here-below with respect to Fig. 5.
  • FIGS 2 and 3 show more details of the safety condenser 26 and its arrangement in the nuclear power plant 1.
  • the heat exchanger 26 of the safety condenser 25 has a substantial cylindrical shape.
  • the upper and lower ends of the heat exchanger 26 may have a dome shape.
  • a voluminous dome shape may facilitate inspection.
  • the safety condenser 25 comprises the heat exchanger 26 and a pool 30.
  • the heat exchanger 26 is at least partially arranged in a pool 30.
  • the pool 30 has a dimension, such that it can be operated at least 72h.
  • the pool may have a depth of between 3m and 6m.
  • each of them should be able to be operated at least 72h.
  • the pool 30 is provided within the housing 31.
  • the housing 31 is fabricated from concrete.
  • the housing 31 may have an internal liner 32, for example fabricated from steel, in particular provided on or covering the interior side of the housing
  • the housing 31 has a bottom 34 limiting the lower end of the pool 30.
  • the bottom 34 is inclined towards the heat exchanger 26.
  • the heat exchanger 26 is positioned, where the pool 30 is the deepest. This improves the natural circulation of the water in the pool 30.
  • the heat exchanger 26 extends through the pool 30.
  • the heat exchanger 26 extends vertically through the pool 30.
  • the pool 30 is covered at its upper end with a covering 36.
  • the heat exchanger 26 extends through the bottom 34 and the covering 36 of the housing 31.
  • the dome shaped upper and lower ends of the heat exchanger 26 are arranged outside the housing 31 , in particular to allow tube inspection without the need to drain the pool 30.
  • the housing 31 comprises a first opening 38 in the covering 36 and the second opening 40 in the bottom 34.
  • the first and second openings 38, 40 are vertically aligned to each other.
  • the first opening 38 has a larger diameter than the second opening 40.
  • the first and second openings 38, 40 are circular shaped.
  • the housing 31 may have substantial rectangular shape, wherein each of the side walls 42 have a (horizontal) length of about 10 to 20m.
  • the pool or the housing may have a circular horizontal cross section.
  • the housing 31 is provided with a third opening 44 in the covering 36 which is provided for discharging steam outside the housing 31 , for example via a discharge chimney (not shown). Below the third opening 44 and above a nominal water level 46 the housing 31 an area 48 is provided in which the steam may be collected.
  • the area 48 is delimited with a grid plate 50 at its lower end and above the nominal water level 44.
  • the grid plate 50 may be made from austenitic steel.
  • the grid plate can be used as a platform from which the descend into the pool can be taken via a ladder for inspection of the safety condenser tubes outer shells and other pool internals.
  • the grid plate is provided for partial de-entrainment of water droplets from the generated steam escaping the pool.
  • the grid plate 50 is positioned such that steam generated from the water in the pool and escaping through the third opening 44 has to pass through the grid plate 50.
  • the nominal water level 44 is the water level of the pool during normal operation of the nuclear reactor (i.e. when the safety condenser 25 is not in operation).
  • the heat exchanger 26 comprises a plurality of parallel heat exchanger tubes 52 extending between an upper end dome 54 and a lower end dome 56.
  • the heat exchanger tubes 52 form a bundle of parallel heat exchanger tubes 52.
  • the bundle of parallel heat exchanger tubes has, in a plane orthogonal to the longitudinal axis X of the safety condenser, a substantial circular shape.
  • the diameter of the bundle of parallel heat exchanger tubes 52 is smaller than the diameter of the first and second openings 38, 40.
  • the upper end dome 54 and the lower end dome 56 are arranged or located outside the pool 30 and/or outside the housing 31. According to embodiments, the heat exchanger tubes 52 are straight tubes.
  • the upper end dome 54 and the lower end dome 56 have respectively a semi spherical shape.
  • the upper end dome 54 and the lower end dome 56 may also have other shapes, for example a cylindrical shape.
  • the heat exchanger tubes 52 are rectilinear tubes, in particular extending in a vertical direction, in particular when installed in the housing 31 .
  • the heat exchanger 26 may comprise between 400 and 700 heat exchanger tubes 52, for example between 500 and 600 heat exchanger tubes 52.
  • the heat exchanger tubes 52 may have a nominal diameter between DN 30 and DN 50.
  • the lengths of the heat exchanger tubes 52 is between 4m and 8m, for example between 5m and 7m.
  • the heat exchanger tubes 52 may be arranged in a square pitch.
  • the center distance between the heat exchanger tubes 52 may be between 40mm and 100mm.
  • the heat exchanger tubes 52 extend into the end domes 52, 54 respectively in an upper tube sheet 58 in the upper end dome 54 and a lower tube sheet 60 in the lower end dome 56.
  • the heat exchanger tubes 52 end respectively in the upper tube sheet 58 and the lower tube sheet 60.
  • the upper and lower tube sheets 58, 60 have respectively a circular shape in a plane orthogonal to the longitudinal axis X of the heat exchanger 26.
  • the upper tube sheet 58 is arranged at the upper end of the heat exchanger tubes 52.
  • the upper tube sheet 58 and/or the lower tube sheet 60 are positioned at least partially outside of the housing, in particular to allow inspection of the pressure-loaded welding seams.
  • the tube sheets have a thickness (extension in direction of the longitudinal axis X) of between 0.4 and 0.8 m.
  • the heat exchanger 26 further comprises a support frame 62 for holding the heat exchanger tubes 52.
  • the support frame 62 includes a plurality of tube support plates 63a and one or more tie rods 63b.
  • the support frame 62 may include 3 to 10 tube support plates, in particular 4 to 7.
  • the tube support plates 63a are spaced apart from each other, for example in regular distances.
  • the tube support plates 63a have a high water permeability.
  • the tube support plates 63a are provided with holes, in particular broached holes.
  • the tube support plates 63a are adapted to maintain regular spacing between the tubes 52 and to limit tube vibration.
  • the tube support plate hole geometry allows longitudinal growth of the straight tube bundle length.
  • the tie rods 63b are connected to the upper tube sheet 58 and/or the lower tube sheet 60.
  • the tie rods 63b support the tube support plates 63a, in particular maintain regular vertical spacing of the tube support plates 63a.
  • the bundle of heat exchanger tubes 52 is surrounded by a flow skirt 64.
  • the flow skirt 64 is formed by a circular steel sheet.
  • the flow skirt may further comprise a vertical frame and/or stringers for a stabilization
  • the flow skirt 64 covers more than 50 percent of the length of the bundle of heat exchanger tubes 52.
  • the flow skirt is connected via the one or more tie rods 63b to the tube support plates 63a and/or a lower ring-shaped support frame 66. Further, the flow skirt is, in an embodiment, connected to an upper sealing support 76 or a lower support frame 66. The connection of flow skirt to the tube support plates 63a is sufficient. The stabilisation of additional tie rods 63b serves the purpose to hold the flow skirt in place in order to prevent the flow skirt from sliding downwards.
  • the flow skirt improves flow circulation during operation of the safety condenser.
  • the lower tube sheet 60 is connected to a ring-shaped support frame 66, in particular in a fluid tight manner.
  • the support frame 66 forms a collar.
  • the lower tube sheet 60 is arranged at the lower end of the heat exchanger tubes 52.
  • the support frame 66 has a larger diameter than the opening 40.
  • the support from is adapted to be supported by the bottom 34 of the housing 31 .
  • a seal is provided between the bottom 34 and the ring-shaped support frame 66, in particular a seal is provided between the internal liner 32 and the support frame 66.
  • the seal may be a welding seal.
  • the support frame 66 has smaller diameter compared to the first opening 38, so that the heat exchanger 26 can be installed or replaced via the first opening 38.
  • a skirt support 68 below the lower end dome 56, there is provided a skirt support 68. Depending on the structure of the concrete housing 31 , this skirt support 68 may serve as main or auxiliary support for the heat exchanger’s weight.
  • the lower end dome 56 is further provided with an outlet 70 in particular for the condensate.
  • the outlet 70 is provided at the lower end of the lower end dome 56, in particular on the longitudinal axis X.
  • the upper end dome 54 is provided with a steam inlet 72 for the steam from the steam generator 14.
  • the steam inlet 72 extends in radial direction with respect to a longitudinal axis X of the heat exchanger 26.
  • the sealing arrangement 74 between the upper end dome 54 and the housing 31 is described.
  • the sealing arrangement comprises a ring shaped sealing support 76.
  • the inner opening of the sealing support 76 is larger than the diameter of the bundle of heat exchanger tubes 52, in order to allow a movement of the bundle of heat exchanger tubes 52 with respect to the sealing support 76.
  • the outer diameter of the sealing support 76 has a larger diameter than the first opening 38.
  • the sealing support 76 is supported by the covering 36.
  • the first opening 38 may have a step shaped inner border.
  • the sealing support 76 has a step shaped outer border being at least partially complementary to the steps of the inner border of the first opening 38.
  • a seal 78 is arranged on one of the steps of the inner border of the first opening 38.
  • the seal in an example, may be an elastomeric seal since thermal and mechanical loads are low. In other embodiments, other materials may be used, for example, metallic or ceramic gaskets.
  • the sealing support 76 with, in particular an axial compensator 80 are held in place relative to first opening 38 in the concrete by means of bolted joints.
  • the lower ring-shaped support frame 66 is pressed into its resting place in the concrete structures of the housing 31 due to its own weight and the weight of the pool water.
  • the axial compensator 80 in particular having a ring shape, is fixed to the upper tube sheet 58 or the upper end dome 54 on its inner side and fixed to the sealing support 76 on its outer side.
  • the axial compensator 80 enables an axial movement along the longitudinal axis X of the upper end of the heat exchanger 26 with respect to the sealing support 76 and/or the housing 31 while being fluid or air tight.
  • a shielding baffle 82 which is fixed to the upper end dome 54 and/or to the upper tube sheet 58.
  • the shielding baffle 82 has a ring shape and surrounds the bundle of parallel heat exchanger tubes 52.
  • the extension in direction of the longitudinal axis X of the heat exchanger is greater than the extension of the axial compensator 80 in direction of the longitudinal axis X.
  • the shielding baffle 82 protects the axial compensator 80 from the thermal radiation from the heat exchanger tubes 52 and/or the upper tube sheet 58.
  • the shielding baffle 82 is arranged spaced apart from the heat exchanger tubes 52 and/or the axial compensator 80.
  • the support frame 84 for attenuators may be connected to the upper end dome 54, measurement equipment, a constant hanger 86, fixed points for an inspection gear and the like.
  • the attenuators may reduce lateral movements of the component.
  • the support frame 84 extends over the upper end dome 54 and is supported by the sealing support 76 and/or the covering 36.
  • the constant hanger 86 is connected between the tip of the upper end dome 54 and the support frame 84.
  • a constant hanger 86 can be used to install the entire tubular and compact structure of the heat exchanger 26 in partial suspended set-up depending on the condition in the reactor building.
  • the housing 31 may have a drain pipe 88 for evacuating the water in the pool.
  • the drain pipe 88 is positioned at the lowest point of the bottom 34 of the pool 30 in the housing 31 .
  • Fig. 3 shows in more detail the installation of the safety condenser 25 and the heat exchanger 26.
  • the safety condenser 25 is preferably placed as high above the steam generator 14 (or the steam generating component in general) as possible in the reactor building to allow a connection of the return line 98 to the steam source in the upper part of the steam generator, preferably at the height of its feedwater manifold in case of a PWR or above the reactor core in the reactor pressure vessel 7’ of a BWR as shown later with respect to Figure 5.
  • the steam generator 14 has a steam dome 90, which collects the steam generated on the secondary side of the steam generator 14.
  • the steam generator 14 has an outlet pipe 92 connected to the outlet 28 in order to guide the steam towards a turbine (not shown) in the water-steam cycle or secondary cooling circuit.
  • a safety condenser charge line 94 branches off the outlet pipe 92 via an optional valve 96 to provide the steam to the heat exchanger tubes 52 of the safety condenser 25.
  • the return line 98 is connected between the outlet 70 of the heat exchanger 26 and the steam generator 14.
  • the return line 98 from the safety condenser 25 connects to the steam generator 14 at the height of the return line, in particular at the height of a feed water manifold, in particular to allow mixing of condensate from the safety condenser with the water circulating in the secondary circuit 16 in the steam generator 14, for example to avoid thermal load to the components.
  • the return line 98 comprises one or more return line valves 100, 101 , in particular at least two return line valves 100, 101.
  • the return line comprises at least one return line control valve 100 for adjusting the heat exchange capacity of the heat exchanger 26 and at least one return line cut-off valve 101 connected in parallel to the at least one return line control valve 100.
  • the return line valves 100, 101 are arranged in parallel branches of the return line 98 and can be operated independently from each other in order to control flow in the return line 98. .
  • the at least one return line control valve 100 is operated to control the functioning of the power of the safety condenser 25, for example by controlling the water level in the heat exchanger tubes 52.
  • the water level in the heat exchanger tubes 52 may be controlled by means of throttling the condensate flow from the safety condenser 25 back to the steam generator 14.
  • the water level inside the safety condenser 25, in particular in the heat exchanger tubes 52 of the heat exchanger 26, directly correlates with its heat removal capacity.
  • the return line valves 100, 101 may be pneumatically actuated.
  • the at least one return line cut-off valve 101 is opened by the passive pressure-pulse transmitter (PPPT) 102.
  • the at least one return line cut-off valve 101 is a normally closed valve.
  • the steam generator 14 is optionally provided with a PPPT 102 (fig. 4).
  • the PPPT is adapted to trigger at least one of the return line cut-off valves 101 in at least one of the branches of the return line 98.
  • FIG 4 show schematically the PPPT 102.
  • the PPPT 102 is for example a small heat exchanger, in particular no larger than approximately 0.030 m 3 .
  • the PPPT includes two compartments, namely a primary chamber 106 and secondary chamber 107.
  • the primary chamber 106 is connected to a vertical pipe 1 18 via a first, top nozzle 108 and a second, bottom nozzle 110, see Figures 3 and 5 in parallel to the steam generator 14 to which it is connected.
  • the top nozzle 108 of the PPPT primary chamber 106 is connected via the vertical pipe 1 18 to the top of the steam generator 14, in particular to the secondary side of the steam generator 14, and the bottom nozzle 1 10 of the PPPT primary chamber 106 is connected via the vertical pipe 118 to the bottom of the secondary side of the steam generator 14. Both ends of the vertical pipe 118 connected to the PPPT primary chamber 106 are connected to the secondary side of the steam generator 14.
  • the secondary chamber 107 of the PPPT 106 is isolated from the steam generator 14.
  • the secondary chamber 107 is separated from the primary chamber 106 with a wall or sheet 1 1 1.
  • the wall or sheet 11 1 is essentially vertically arranged.
  • the PPPT further includes one or more blind tubes 112 extending from the wall 1 11 into the primary chamber 106.
  • the blind tubes 1 12 extend horizontally.
  • the primary chamber 106 may include filler tubes 1 13, in particular in parallel and/or above the blind tubes 1 12 in order to reduce the volume of the primary chamber.
  • the blind tubes 112 are open towards to secondary chamber 107. In other words, the blind tubes 1 12 are in fluid connection with the secondary chamber 107.
  • the primary chamber 106 is filled with water.
  • the secondary chamber 107 is filled with water, at least above the level of the blind tubes 112.
  • the secondary has also a top nozzle 114 and a bottom nozzle 1 16.
  • the top nozzle 114 is provided for venting and/or filling. During normal operation, the top nozzle 114 is closed, in particular in order to build up the pressure.
  • the bottom nozzle 1 16 is connected to the at least one return line cut-off valve 101 , in order to activate (open) the return line cutoff valve 101 .
  • the fill level on the secondary side of the steam generator 14 drops and the level inside the vertical pipe 118 does likewise.
  • the PPPT primary chamber 106 starts to fill with steam, thus starting to heat the secondary chamber 107 via a heat exchange across the blind tubes 1 12.
  • the water in the secondary chamber 107 of the PPPT 102 heats and evaporates and creates a hydraulic pulse from the bottom nozzle 1 16, which can in particular be used to trigger valve pilots of the return line cut-off valve 101.
  • the valve pilot initiates the complete opening of the return line cut-off valve 101 , which puts the safety condenser 25 in operation.
  • the PPPT is adapted to emit a hydraulic pulse towards at least one of the return line valves 101 , in particular the at least one return line cut-off valve 101 .
  • solenoid-actuated pilots which react to the loss of electricity may be used to initiate the opening of the return line cut-off valve 101 in the return line 98.
  • the safety condenser 25 functions as follows.
  • the safety condenser 25 provides a further closed circuit with an integrated heat exchanger, which comprises water as a heat sink.
  • the safety condenser 25 enables the condensation of steam, which is still generated for example by the decay heat in the steam generating component, for example the steam generator 14 of a pressurized water reactor (fig. 1 ) due to the heat still transported in the primary cooling circuit 10. In all cases, heat is therefore transmitted to the water in the pool 30.
  • the condensed water is then again provided to the steam generator 14 via the return line 98.
  • the vertically arranged heat exchanger tubes 52 enable a control or limitation of the power of the safety condenser 25.
  • a limitation or control of the safety condenser 25 is useful as the safety condenser 25 could also be used during accident conditions and transients, which require controlled cool-down of the facility, steam generator tube ruptures, for instance.
  • the control of the safety condenser 25 functions as follows. Due to the regulation of the condensate flow rate by the return line control valve 100 in the return line 98 towards the steam generator 14 the safety condenser 26 is controlled.
  • the condensate fill level in the heat exchanger tubes 52 rises to a specific level.
  • the part of the heat exchanger tubes 52, which is filled with water (i.e. the condensed steam) do not transfer much heat to the water in the pool 30.
  • the surface in the heat exchanger 26, which is provided for the heat transfer towards the water in the pool 30 is therefore reduced. In other words, the level of the water in the heat exchanger tubes 52 determines the limit of heat exchange capacity of the safety condenser 26.
  • the vertical heat exchanger tubes 52 therefore simplifies the control the safety condenser 26 as only the geometry of the vertically arranged heat exchanger tubes 52 have to be taken into account.
  • the heat exchange capacity of the heat exchanger 26 is proportional to the height of the space in the heat exchanger tubes 52 not occupied by condensate. Therefore, the heat exchange capacity of the heat exchanger 26 can be easily controlled by the above-mentioned device.
  • the vertical arrangement of the heat exchanger 26 simplifies the mounting of the heat exchanger 26 and access to the upper and lower end dome 54, 56, which may contain openings for the service. Further, the upper and lower end dome 54, 56 may contain access to measurement equipment.
  • the heat exchanger 26 can be delivered completely with all necessary connections and simply installed in the housing. Only a few weldings have to be made within the pool 30. Further, many of the seals are sealing due to the weight of the heat exchanger 26. According to embodiments, the number of the weldings that are subject to thermal and physical stress is minimized. Thus, the connections between components of the heat exchanger 26 are subject either to physical stress or to thermal stress.
  • FIG. 5 provides a simplified schematic overview on a nuclear power plant 1 ’ with a boiling water reactor (BWR) 120.
  • the same features are designated with the same reference sign as in Figure 1 .
  • the boiling water reactor comprises a reactor pressure vessel 7’.
  • the steam is generated directly in the reactor pressure vessel 7’ thus making the reactor pressure vessel 7’ itself acting as the steam-generating component - in its function similar to the steam generator 14 in a pressurized water reactor 3.
  • one or more recirculation pumps 122 are arranged inside the reactor pressure vessel 7’.
  • the reactor pressure vessel is connected to a water-steam cycle line 124 via at least one outlet 126 of the reactor pressure vessel 7’.
  • the steam produced in the reactor pressure vessel 7’ of the boiling water reactor is guided to one or more turbines 18 via the at least one first outlet 126, which is arranged at an upper end of the reactor pressure vessel 7’, and the water-steam cycle line 124, which drives respectively a generator 20 to produce electricity.
  • the steam is further guided from the turbine 18 to a condenser 22, where it is cooled down and condensed. Then it is pumped by a condensate pump 24 back to the reactor pressure vessel 7’.
  • the reactor pressure vessel 7’ has a steam dome 90, which collects the steam generated in the core 5 of the reactor pressure vessel 7’.
  • the safety condenser provides an additional heat sink for the reactor coolant, here the water in the primary circuit.
  • the reactor pressure vessel 7’ comprises a second outlet or outlet nozzle 128, which is connected to the safety condenser charge line 94.
  • the second outlet 128 may be alternatively also connected to the first outlet 126.
  • the safety condenser charge line 94 is connected to the steam generating component 7’, in particular in form of the reactor pressure vessel.
  • the second end of the heat exchanger 26, in particular via the return line 98, is connected to the reactor pressure vessel 7’, in particular above the reactor core 5.
  • the safety condenser 25 described here-above is connected to the steamgenerating component in a water-cooled nuclear reactor.in case of a boiling water reactor to the reactor pressure vessel 7’.
  • the safety condenser 25 and related components can also be installed at the steam generating component of a light-water cooled nuclear reactor using a watersteam cycle as driving medium for the turbine or as a heat sink for removing decay power.
  • the steam generating component is the reactor pressure vessel 7’. Accordingly, for application in a boiling water reactor, the safety condenser 25 and the passive pressure pulse transmitter 102 together with its vertical pipe 118 are directly connected to the reactor pressure vessel 7’.
  • Technical functionality and means to control and limit the heat removal capacity of the safety condenser 25 remain the same as for the application in a pressurized water reactor 3.
  • the fill level in the PPPT 102 and related vertical pipe 118 reflect the water level in the RPV 7’, see Figure 5. Both ends of the vertical pipe 1 18 are connected to the RPV 7’. If the water level in the reactor pressure vessel 7’ falls short of a certain level - which must be chosen in order to secure sufficient water coverage of the core at all times - the passive pressure pulse transmitter 102 activates the safety condenser 25 as described above by opening the return line cut-off valve 101 . The safety condenser 25 then acts as the ultimate heat sink for the steam source connected to the in and outlets of the safety condenser.
  • any feature of any embodiment described herein may be used in combination with any feature of any other embodiment described herein.

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Abstract

The present invention relates to a safety condenser (25) intended to be connected to a steam generating component (14, 7') in a water-cooled nuclear reactor (3, 120) comprising: - a heat exchanger (26) partially arranged in a pool (30) containing a cooling fluid, the heat exchanger (26) comprising a bundle of parallel heat exchanger tubes (52), the heat exchanger tubes extending in a vertical direction between a lower tube sheet (60) and a upper tube sheet (58), each heat exchanger tube (52) being intended for receiving a downward flow of steam from the steam generating component (14, 7'), the heat exchanger comprising an inlet (72), intended for receiving steam generated in the steam generating component(7', 14), the heat exchanger (26) being configured for cooling this steam through heat exchange with the cooling fluid contained in the pool (30) to produce condensate and an outlet (70), configured for returning the condensate to the steam generating component; and - a cooling capacity regulator (100), configured for controlling the cooling capacity of the safety condenser (26) by adjusting the height of the condensate in the heat exchanger tubes, wherein the heat exchanger (26) further comprises a lower end dome (56) connected to the lower tube sheet (60) and comprising the outlet (70) intended to be connected to the steam generating component (7', 14) and upper end dome (54) connected to the upper tube sheet (58) and comprising the inlet (72) intended to be connected to an outlet pipe (92) of the steam generating component (7', 14), the lower end dome (56) and the upper end dome (54) being located outside of the pool (30).

Description

Safety condenser and nuclear reactor containing the same
The present invention concerns a safety condenser intended to be connected to a steam generator in a nuclear reactor.
Further, the present invention relates to a nuclear reactor.
US 4,765,946 discloses a safety condenser intended to be connected to a steam generator in a nuclear reactor, comprising a heat exchanger arranged in a pool containing a cooling fluid, the heat exchanger comprising a bundle of parallel heat exchanger tubes.
WO 93/04481 discloses a safety condenser intended to be connected to a steam generator in a nuclear reactor, comprising a heat exchanger arranged in a pool containing a cooling fluid, the heat exchanger comprising a bundle of heat exchanger tubes.
WO 93/04480 discloses a safety condenser intended to be connected to a steam generator in a nuclear reactor, comprising a heat exchanger comprising a bundle of heat exchanger tubes.
Object of the present invention is to provide a safety condenser for a steam generator, which has a heat exchange capacity, which can be easily adjusted depending on the needs.
According to one aspect, a safety condenser intended to be connected to a steam generating component in a water-cooled nuclear reactor is provided comprising:
- a heat exchanger partially arranged in a pool containing a cooling fluid, the heat exchanger comprising a bundle of parallel heat exchanger tubes, the heat exchanger tubes extending in a vertical direction between a lower tube sheet and a upper tube sheet, each heat exchanger tube being intended for receiving a downward flow of steam from the steam generating component, the heat exchanger comprising an inlet, intended for receiving steam generated in the steam generating component, the heat exchanger being configured for cooling this steam through heat exchange with the cooling fluid contained in the pool to produce condensate and an outlet, configured for returning the condensate to the steam generating component; and
- a cooling capacity regulator, configured for controlling the cooling capacity of the safety condenser by adjusting the height of the condensate in the heat exchanger tubes, wherein the heat exchanger further comprises a lower end dome connected to the lower tube sheet and comprising the outlet intended to be connected to the steam generating component and upper end dome connected to the upper tube sheet and comprising the inlet intended to be connected to an outlet pipe of the steam generating component, the lower end dome and the upper end dome being located outside of the pool. Further embodiments may relate to one or more of the following features, which may be combined in any technical feasible combination:
• the lower end dome and the upper end dome have a semi-spherical shape;
• the pool is arranged in a housing, the housing having a first opening in a covering and a second opening in the bottom, the first and second openings are vertically aligned to each other, wherein the heat exchanger extends through the first and second openings.
• the lower end dome and the upper end dome being located outside of the housing;
• the lower tube sheet is connected to a support frame having a larger outer diameter than the diameter of the second opening, wherein in particular the support frame has a smaller outer diameter than the diameter of the first opening;
• The safety condenser further comprising a sealing arrangement between the upper end dome and the housing, wherein the sealing arrangement comprises an axial compensator enabling an axial movement along the longitudinal axis of the heat exchanger of the upper end of the heat exchanger with respect to the housing;
• a shielding baffle is arranged spaced apart from the heat exchanger tubes and/or the axial compensator;
• The safety condenser further comprising a sealing support, wherein the outer diameter of the sealing support has a larger diameter than the first opening, wherein the axial compensator is fixed to the sealing support;
• the first opening has a step shaped inner border and the sealing support has a step shaped outer border being at least partially complementary to the steps of the inner border of the first opening;
• the cooling capacity regulator comprises at least one valve, in particular a plurality of valves being connected in parallel, wherein the at least one valve is arranged in a return line between the outlet and the steam generating component;
• the bundle of heat exchanger tubes is at least partially surrounded by a flow skirt, wherein in particular the flow skirt covers at least 50 percent of the length of the bundle of heat exchanger tubes; and/or
• the heat exchanger tubes are straight tubes.
According to another aspect, a water-cooled nuclear reactor is provided comprising a safety condenser according to an embodiment disclosed herein.
Further embodiments may relate to one or more of the following features, which may be combined in any technical feasible combination:
• the steam generating component is a steam generator of a pressurized water reactor or a reactor pressure vessel of a boiling water reactor. • The water-cooled nuclear reactor further comprising a steam generating component, wherein the inlet of the heat exchanger is connected to an outlet pipe of the steam generating component and the outlet of the heat exchanger is connected to the steam generating component.
• The water-cooled nuclear reactor further comprising a passive pressure pulse transmitter adapted to emit a hydraulic pulse towards at least one of the return line valves in case the water level in the steam generating component falls below a predetermined level.
• the nuclear reactor utilizes light water as primary cooling medium.
Further advantages, features, aspects and details are evident from the dependent claims, the description and the drawings.
The accompanying drawings relate to embodiments of the invention and are described in the following:
Fig. 1 shows schematically a nuclear power plant with a pressurized water reactor;
Fig. 2 shows schematically a safety condenser according to an embodiment;
Fig. 3 shows schematically the connection of the safety condenser to the steam generator for a pressurized water reactor;
Fig. 4 shows schematically the structures and function of the passive pressure pulse transmitter (PPPT); and
Fig. 5 shows schematically the connection of the safety condenser to the reactor pressure vessel of a boiling water reactor.
FIG. 1 provides a simplified schematic overview of a nuclear power plant 1 with a nuclear reactor in form of a pressurized water reactor (PWR) 3. The PWR 3 comprises a reactor core 5 having a reactor pressure vessel (RPV) 7. During operation, the heat produced by the reactor core 5 within 20 the reactor pressure vessel 7 is transferred by a primary cooling medium, for example water, circulating in a primary cooling circuit 10 under the driving force of a reactor coolant pump (RCP) 12, or - in case of operation in emergency power mode - under natural circulation (convective flow). The primary cooling circuit includes one or more steam generators 14, in which the heat of the primary cooling medium is transferred to a secondary cooling medium circulating in a secondary cooling circuit 16, thereby evaporating the secondary cooling medium. The primary cooling medium is then conducted again into the reactor core 5 by the RCP 12. The secondary cooling circuit 16 is for a water-steam cycle.
In the secondary cooling circuit 16, the steam is guided to one or more turbines 18, which drives respectively a generator 20 to produce electricity. The steam is further guided from the turbine 18 to a condenser 22, where it is cooled down and condensed. Then it is pumped by a second pump 24 back to the one or more steam generator 14, in particular via a return line. The second pump 24 is also called condensate pump.
Further, there is provided at least one safety condenser 25 comprising a heat exchanger 26, in particular a straight-tube heat exchanger 26. The safety condenser 25 described hereafter is connected to the steam-generating component in a water-cooled nuclear reactor. In case of a pressurized water reactor the safety condenser 25 is connected to the steam generator 14.
The heat exchanger 26 is connected at its first end to an outlet 28 of at least one steam generator 14 in the secondary circuit 16 via a charge line and at its second end to a downcomer section 29 of the same steam generator. In an embodiment, the second end of the steam generator 14 is connected to an upper end of the downcomer section 29, in particular to allow mixing with secondary side feed water to reduce thermal stress for the steam generator tube sheet or return line connection nozzles. In an embodiment, the second end is connected to a return line of the secondary cooling circuit 16, wherein the return line returns the condensed steam to the steam generator 14. The first end is the upper end in the drawings and the second end the lower end in the drawings.
Each safety condenser 25 with the heat exchanger 26 is provided to condense the steam produced in the steam generating component, in case of a pressurized water reactor the steam generator 14, for the purpose of removing heat from the decay circuit in case of a failure of feed water supply to the steam generating component. In the following, the details will be described with respect to a single safety condenser 26. As indicated above, more than one, in particular 2, 3, 4 or more safety condenser 26 may be used.
Regardless of light-water cooled nuclear reactor type, the safety condenser 26 provides an additional heat sink for the reactor coolant, for example the secondary cooling medium. For example, in case of a station blackout entailing total loss of feed-water supply, the safety condenser and its pool provide an additional heat sink for the decay heat still generated by the reactor core 5 after shut-down, thus avoiding a continuous level drop in either the steam generator 14 of a PWR 3 or the reactor pressure vessel 7’ of a boiling water reactor explained here-below with respect to Fig. 5.
Figures 2 and 3 show more details of the safety condenser 26 and its arrangement in the nuclear power plant 1. The heat exchanger 26 of the safety condenser 25 has a substantial cylindrical shape. In an embodiment, the upper and lower ends of the heat exchanger 26 may have a dome shape. A voluminous dome shape may facilitate inspection.
As it can be seen from Figure 2, the safety condenser 25 comprises the heat exchanger 26 and a pool 30. The heat exchanger 26 is at least partially arranged in a pool 30. The pool 30 has a dimension, such that it can be operated at least 72h. In an example, the pool may have a depth of between 3m and 6m. For example, in case of multiple safety condensers, each of them should be able to be operated at least 72h.
The pool 30 is provided within the housing 31. For example, the housing 31 is fabricated from concrete.
In an embodiment, the housing 31 may have an internal liner 32, for example fabricated from steel, in particular provided on or covering the interior side of the housing
31 . The housing 31 has a bottom 34 limiting the lower end of the pool 30.
In an embodiment, the bottom 34 is inclined towards the heat exchanger 26. In other words, the heat exchanger 26 is positioned, where the pool 30 is the deepest. This improves the natural circulation of the water in the pool 30.
According to embodiments, which may be combined with other embodiments disclosed herein, the heat exchanger 26 extends through the pool 30. In the embodiment shown the heat exchanger 26 extends vertically through the pool 30.
The pool 30 is covered at its upper end with a covering 36.
In an example, the heat exchanger 26 extends through the bottom 34 and the covering 36 of the housing 31. In an embodiment, the dome shaped upper and lower ends of the heat exchanger 26 are arranged outside the housing 31 , in particular to allow tube inspection without the need to drain the pool 30.
The housing 31 comprises a first opening 38 in the covering 36 and the second opening 40 in the bottom 34. The first and second openings 38, 40 are vertically aligned to each other. The first opening 38 has a larger diameter than the second opening 40. Further, according to an embodiment, the first and second openings 38, 40 are circular shaped.
According to embodiments, from a top view, the housing 31 may have substantial rectangular shape, wherein each of the side walls 42 have a (horizontal) length of about 10 to 20m. In other embodiments, the pool or the housing may have a circular horizontal cross section.
The housing 31 is provided with a third opening 44 in the covering 36 which is provided for discharging steam outside the housing 31 , for example via a discharge chimney (not shown). Below the third opening 44 and above a nominal water level 46 the housing 31 an area 48 is provided in which the steam may be collected. The area 48 is delimited with a grid plate 50 at its lower end and above the nominal water level 44. In an embodiment, the grid plate 50 may be made from austenitic steel. For example the grid plate can be used as a platform from which the descend into the pool can be taken via a ladder for inspection of the safety condenser tubes outer shells and other pool internals. In some embodiments, which may be combined with other embodiments disclosed herein the grid plate is provided for partial de-entrainment of water droplets from the generated steam escaping the pool. For that purpose, the grid plate 50 is positioned such that steam generated from the water in the pool and escaping through the third opening 44 has to pass through the grid plate 50.
The nominal water level 44 is the water level of the pool during normal operation of the nuclear reactor (i.e. when the safety condenser 25 is not in operation).
The heat exchanger 26 comprises a plurality of parallel heat exchanger tubes 52 extending between an upper end dome 54 and a lower end dome 56. The heat exchanger tubes 52 form a bundle of parallel heat exchanger tubes 52. The bundle of parallel heat exchanger tubes has, in a plane orthogonal to the longitudinal axis X of the safety condenser, a substantial circular shape. The diameter of the bundle of parallel heat exchanger tubes 52 is smaller than the diameter of the first and second openings 38, 40. The upper end dome 54 and the lower end dome 56 are arranged or located outside the pool 30 and/or outside the housing 31. According to embodiments, the heat exchanger tubes 52 are straight tubes.
In the embodiment shown, the upper end dome 54 and the lower end dome 56 have respectively a semi spherical shape. The upper end dome 54 and the lower end dome 56 may also have other shapes, for example a cylindrical shape.
For example, the heat exchanger tubes 52 are rectilinear tubes, in particular extending in a vertical direction, in particular when installed in the housing 31 . The heat exchanger 26 may comprise between 400 and 700 heat exchanger tubes 52, for example between 500 and 600 heat exchanger tubes 52. The heat exchanger tubes 52 may have a nominal diameter between DN 30 and DN 50. In an embodiment, the lengths of the heat exchanger tubes 52 is between 4m and 8m, for example between 5m and 7m. The heat exchanger tubes 52 may be arranged in a square pitch. For example, the center distance between the heat exchanger tubes 52 may be between 40mm and 100mm.
The heat exchanger tubes 52 extend into the end domes 52, 54 respectively in an upper tube sheet 58 in the upper end dome 54 and a lower tube sheet 60 in the lower end dome 56. The heat exchanger tubes 52 end respectively in the upper tube sheet 58 and the lower tube sheet 60. The upper and lower tube sheets 58, 60 have respectively a circular shape in a plane orthogonal to the longitudinal axis X of the heat exchanger 26. The upper tube sheet 58 is arranged at the upper end of the heat exchanger tubes 52.
According to embodiments, the upper tube sheet 58 and/or the lower tube sheet 60 are positioned at least partially outside of the housing, in particular to allow inspection of the pressure-loaded welding seams. The tube sheets have a thickness (extension in direction of the longitudinal axis X) of between 0.4 and 0.8 m. The heat exchanger 26 further comprises a support frame 62 for holding the heat exchanger tubes 52. The support frame 62 includes a plurality of tube support plates 63a and one or more tie rods 63b. For example, the support frame 62 may include 3 to 10 tube support plates, in particular 4 to 7. The tube support plates 63a are spaced apart from each other, for example in regular distances.
According to embodiments, the tube support plates 63a have a high water permeability. For example the tube support plates 63a are provided with holes, in particular broached holes. The tube support plates 63a are adapted to maintain regular spacing between the tubes 52 and to limit tube vibration. The tube support plate hole geometry allows longitudinal growth of the straight tube bundle length.
The tie rods 63b are connected to the upper tube sheet 58 and/or the lower tube sheet 60. In particular the tie rods 63b support the tube support plates 63a, in particular maintain regular vertical spacing of the tube support plates 63a.
According to an embodiment, the bundle of heat exchanger tubes 52 is surrounded by a flow skirt 64. In an embodiment, the flow skirt 64 is formed by a circular steel sheet. The flow skirt may further comprise a vertical frame and/or stringers for a stabilization
In an example, the flow skirt 64 covers more than 50 percent of the length of the bundle of heat exchanger tubes 52.
According to embodiments, the flow skirt is connected via the one or more tie rods 63b to the tube support plates 63a and/or a lower ring-shaped support frame 66. Further, the flow skirt is, in an embodiment, connected to an upper sealing support 76 or a lower support frame 66. The connection of flow skirt to the tube support plates 63a is sufficient. The stabilisation of additional tie rods 63b serves the purpose to hold the flow skirt in place in order to prevent the flow skirt from sliding downwards.
The flow skirt improves flow circulation during operation of the safety condenser.
The lower tube sheet 60 is connected to a ring-shaped support frame 66, in particular in a fluid tight manner. The support frame 66 forms a collar. The lower tube sheet 60 is arranged at the lower end of the heat exchanger tubes 52. The support frame 66 has a larger diameter than the opening 40. The support from is adapted to be supported by the bottom 34 of the housing 31 . In an embodiment, a seal is provided between the bottom 34 and the ring-shaped support frame 66, in particular a seal is provided between the internal liner 32 and the support frame 66. For example, the seal may be a welding seal. The support frame 66 has smaller diameter compared to the first opening 38, so that the heat exchanger 26 can be installed or replaced via the first opening 38. Further, below the lower end dome 56, there is provided a skirt support 68. Depending on the structure of the concrete housing 31 , this skirt support 68 may serve as main or auxiliary support for the heat exchanger’s weight.
The lower end dome 56 is further provided with an outlet 70 in particular for the condensate. For example, the outlet 70 is provided at the lower end of the lower end dome 56, in particular on the longitudinal axis X.
The upper end dome 54 is provided with a steam inlet 72 for the steam from the steam generator 14. The steam inlet 72 extends in radial direction with respect to a longitudinal axis X of the heat exchanger 26.
In the following, the sealing arrangement 74 between the upper end dome 54 and the housing 31 is described. The sealing arrangement comprises a ring shaped sealing support 76. The inner opening of the sealing support 76 is larger than the diameter of the bundle of heat exchanger tubes 52, in order to allow a movement of the bundle of heat exchanger tubes 52 with respect to the sealing support 76. The outer diameter of the sealing support 76 has a larger diameter than the first opening 38. Thus, the sealing support 76 is supported by the covering 36. In a cross sectional view, the first opening 38 may have a step shaped inner border. According to embodiments, the sealing support 76 has a step shaped outer border being at least partially complementary to the steps of the inner border of the first opening 38. In an embodiment, a seal 78 is arranged on one of the steps of the inner border of the first opening 38. The seal, in an example, may be an elastomeric seal since thermal and mechanical loads are low. In other embodiments, other materials may be used, for example, metallic or ceramic gaskets. The sealing support 76 with, in particular an axial compensator 80 are held in place relative to first opening 38 in the concrete by means of bolted joints. The lower ring-shaped support frame 66 is pressed into its resting place in the concrete structures of the housing 31 due to its own weight and the weight of the pool water.
The axial compensator 80, in particular having a ring shape, is fixed to the upper tube sheet 58 or the upper end dome 54 on its inner side and fixed to the sealing support 76 on its outer side. The axial compensator 80 enables an axial movement along the longitudinal axis X of the upper end of the heat exchanger 26 with respect to the sealing support 76 and/or the housing 31 while being fluid or air tight.
Further, there is provided a shielding baffle 82, which is fixed to the upper end dome 54 and/or to the upper tube sheet 58. The shielding baffle 82 has a ring shape and surrounds the bundle of parallel heat exchanger tubes 52. The extension in direction of the longitudinal axis X of the heat exchanger is greater than the extension of the axial compensator 80 in direction of the longitudinal axis X. Thus, the heat exchanger tubes 52 are protected from a lateral force exerted by the axial compensator 80. Additionally or alternatively, the shielding baffle 82 protects the axial compensator 80 from the thermal radiation from the heat exchanger tubes 52 and/or the upper tube sheet 58. The shielding baffle 82 is arranged spaced apart from the heat exchanger tubes 52 and/or the axial compensator 80.
Further, there may be the support frame 84 for attenuators connected to the upper end dome 54, measurement equipment, a constant hanger 86, fixed points for an inspection gear and the like. The attenuators may reduce lateral movements of the component. The support frame 84 extends over the upper end dome 54 and is supported by the sealing support 76 and/or the covering 36. For example, the constant hanger 86 is connected between the tip of the upper end dome 54 and the support frame 84. In some embodiments, which may be combined with other embodiments disclosed herein, a constant hanger 86 can be used to install the entire tubular and compact structure of the heat exchanger 26 in partial suspended set-up depending on the condition in the reactor building.
In some embodiments, the housing 31 may have a drain pipe 88 for evacuating the water in the pool. The drain pipe 88 is positioned at the lowest point of the bottom 34 of the pool 30 in the housing 31 .
Fig. 3 shows in more detail the installation of the safety condenser 25 and the heat exchanger 26. The safety condenser 25 is preferably placed as high above the steam generator 14 (or the steam generating component in general) as possible in the reactor building to allow a connection of the return line 98 to the steam source in the upper part of the steam generator, preferably at the height of its feedwater manifold in case of a PWR or above the reactor core in the reactor pressure vessel 7’ of a BWR as shown later with respect to Figure 5.
The steam generator 14 has a steam dome 90, which collects the steam generated on the secondary side of the steam generator 14. The steam generator 14 has an outlet pipe 92 connected to the outlet 28 in order to guide the steam towards a turbine (not shown) in the water-steam cycle or secondary cooling circuit.
A safety condenser charge line 94 branches off the outlet pipe 92 via an optional valve 96 to provide the steam to the heat exchanger tubes 52 of the safety condenser 25.
Further, the return line 98 is connected between the outlet 70 of the heat exchanger 26 and the steam generator 14. The return line 98 from the safety condenser 25 connects to the steam generator 14 at the height of the return line, in particular at the height of a feed water manifold, in particular to allow mixing of condensate from the safety condenser with the water circulating in the secondary circuit 16 in the steam generator 14, for example to avoid thermal load to the components. The return line 98 comprises one or more return line valves 100, 101 , in particular at least two return line valves 100, 101. For example the return line comprises at least one return line control valve 100 for adjusting the heat exchange capacity of the heat exchanger 26 and at least one return line cut-off valve 101 connected in parallel to the at least one return line control valve 100. Connected in parallel means that the return line valves 100, 101 are arranged in parallel branches of the return line 98 and can be operated independently from each other in order to control flow in the return line 98. . The at least one return line control valve 100 is operated to control the functioning of the power of the safety condenser 25, for example by controlling the water level in the heat exchanger tubes 52. The water level in the heat exchanger tubes 52 may be controlled by means of throttling the condensate flow from the safety condenser 25 back to the steam generator 14. The water level inside the safety condenser 25, in particular in the heat exchanger tubes 52 of the heat exchanger 26, directly correlates with its heat removal capacity. According to an embodiment, the return line valves 100, 101 may be pneumatically actuated.
In an embodiment, the at least one return line cut-off valve 101 is opened by the passive pressure-pulse transmitter (PPPT) 102. The at least one return line cut-off valve 101 is a normally closed valve.
As it can be seen from Figure 3, the steam generator 14 is optionally provided with a PPPT 102 (fig. 4). The PPPT is adapted to trigger at least one of the return line cut-off valves 101 in at least one of the branches of the return line 98.
Figure 4 show schematically the PPPT 102. The PPPT 102 is for example a small heat exchanger, in particular no larger than approximately 0.030 m3. The PPPT includes two compartments, namely a primary chamber 106 and secondary chamber 107. The primary chamber 106 is connected to a vertical pipe 1 18 via a first, top nozzle 108 and a second, bottom nozzle 110, see Figures 3 and 5 in parallel to the steam generator 14 to which it is connected. The top nozzle 108 of the PPPT primary chamber 106 is connected via the vertical pipe 1 18 to the top of the steam generator 14, in particular to the secondary side of the steam generator 14, and the bottom nozzle 1 10 of the PPPT primary chamber 106 is connected via the vertical pipe 118 to the bottom of the secondary side of the steam generator 14. Both ends of the vertical pipe 118 connected to the PPPT primary chamber 106 are connected to the secondary side of the steam generator 14. The secondary chamber 107 of the PPPT 106 is isolated from the steam generator 14.
The secondary chamber 107 is separated from the primary chamber 106 with a wall or sheet 1 1 1. The wall or sheet 11 1 is essentially vertically arranged.
The PPPT further includes one or more blind tubes 112 extending from the wall 1 11 into the primary chamber 106. For example, the blind tubes 1 12 extend horizontally. In some embodiments, the primary chamber 106 may include filler tubes 1 13, in particular in parallel and/or above the blind tubes 1 12 in order to reduce the volume of the primary chamber. The blind tubes 112 are open towards to secondary chamber 107. In other words, the blind tubes 1 12 are in fluid connection with the secondary chamber 107.
In normal operation of the nuclear power plant, the primary chamber 106 is filled with water. Also, the secondary chamber 107 is filled with water, at least above the level of the blind tubes 112.
The secondary has also a top nozzle 114 and a bottom nozzle 1 16. The top nozzle 114 is provided for venting and/or filling. During normal operation, the top nozzle 114 is closed, in particular in order to build up the pressure. The bottom nozzle 1 16 is connected to the at least one return line cut-off valve 101 , in order to activate (open) the return line cutoff valve 101 .
For example, in case of a blackout of the nuclear power plant or total loss-of- feedwater, the fill level on the secondary side of the steam generator 14 drops and the level inside the vertical pipe 118 does likewise. At the installation height of the PPPT 102, the PPPT primary chamber 106 starts to fill with steam, thus starting to heat the secondary chamber 107 via a heat exchange across the blind tubes 1 12.
The water in the secondary chamber 107 of the PPPT 102 heats and evaporates and creates a hydraulic pulse from the bottom nozzle 1 16, which can in particular be used to trigger valve pilots of the return line cut-off valve 101. In an embodiment, by using pneumatic additional loads, the valve pilot initiates the complete opening of the return line cut-off valve 101 , which puts the safety condenser 25 in operation. Thus, if the level in the steam generating component, for example the steam generator 14 in Figure 1 , drops below a predetermined level, in particular corresponding to the installation level of the PPPT 102, the PPPT is adapted to emit a hydraulic pulse towards at least one of the return line valves 101 , in particular the at least one return line cut-off valve 101 .
In an alternative embodiment, solenoid-actuated pilots, which react to the loss of electricity may be used to initiate the opening of the return line cut-off valve 101 in the return line 98.
Generally, the safety condenser 25 functions as follows. The safety condenser 25 provides a further closed circuit with an integrated heat exchanger, which comprises water as a heat sink. The safety condenser 25 enables the condensation of steam, which is still generated for example by the decay heat in the steam generating component, for example the steam generator 14 of a pressurized water reactor (fig. 1 ) due to the heat still transported in the primary cooling circuit 10. In all cases, heat is therefore transmitted to the water in the pool 30. The condensed water is then again provided to the steam generator 14 via the return line 98. Thus, the safety condenser 25 increases the security of the nuclear power plant 1. The vertically arranged heat exchanger tubes 52 enable a control or limitation of the power of the safety condenser 25. A limitation or control of the safety condenser 25 is useful as the safety condenser 25 could also be used during accident conditions and transients, which require controlled cool-down of the facility, steam generator tube ruptures, for instance.
The control of the safety condenser 25 functions as follows. Due to the regulation of the condensate flow rate by the return line control valve 100 in the return line 98 towards the steam generator 14 the safety condenser 26 is controlled. The condensate fill level in the heat exchanger tubes 52 rises to a specific level. The part of the heat exchanger tubes 52, which is filled with water (i.e. the condensed steam) do not transfer much heat to the water in the pool 30. The surface in the heat exchanger 26, which is provided for the heat transfer towards the water in the pool 30 is therefore reduced. In other words, the level of the water in the heat exchanger tubes 52 determines the limit of heat exchange capacity of the safety condenser 26. The vertical heat exchanger tubes 52 therefore simplifies the control the safety condenser 26 as only the geometry of the vertically arranged heat exchanger tubes 52 have to be taken into account.
Thanks to the vertical arrangement of the heat exchanger tubes 52, the heat exchange capacity of the heat exchanger 26 is proportional to the height of the space in the heat exchanger tubes 52 not occupied by condensate. Therefore, the heat exchange capacity of the heat exchanger 26 can be easily controlled by the above-mentioned device. The vertical arrangement of the heat exchanger 26 simplifies the mounting of the heat exchanger 26 and access to the upper and lower end dome 54, 56, which may contain openings for the service. Further, the upper and lower end dome 54, 56 may contain access to measurement equipment. For example, the heat exchanger 26 can be delivered completely with all necessary connections and simply installed in the housing. Only a few weldings have to be made within the pool 30. Further, many of the seals are sealing due to the weight of the heat exchanger 26. According to embodiments, the number of the weldings that are subject to thermal and physical stress is minimized. Thus, the connections between components of the heat exchanger 26 are subject either to physical stress or to thermal stress.
Further, due to the arrangement of the upper and lower end domes 54, 56 of the heat exchanger 26 outside the housing 31 , they are not in contact with the water in the pool 30, so that the equipment connected to the lower and upper end domes 54, 56 require less requirements with respect to ingredients of the water.
FIG. 5 provides a simplified schematic overview on a nuclear power plant 1 ’ with a boiling water reactor (BWR) 120. The same features are designated with the same reference sign as in Figure 1 . The boiling water reactor comprises a reactor pressure vessel 7’. In a boiling water reactor, the steam is generated directly in the reactor pressure vessel 7’ thus making the reactor pressure vessel 7’ itself acting as the steam-generating component - in its function similar to the steam generator 14 in a pressurized water reactor 3. Inside the reactor pressure vessel 7’, one or more recirculation pumps 122 are arranged.
The reactor pressure vessel is connected to a water-steam cycle line 124 via at least one outlet 126 of the reactor pressure vessel 7’.
The steam produced in the reactor pressure vessel 7’ of the boiling water reactor is guided to one or more turbines 18 via the at least one first outlet 126, which is arranged at an upper end of the reactor pressure vessel 7’, and the water-steam cycle line 124, which drives respectively a generator 20 to produce electricity. The steam is further guided from the turbine 18 to a condenser 22, where it is cooled down and condensed. Then it is pumped by a condensate pump 24 back to the reactor pressure vessel 7’.
The reactor pressure vessel 7’ has a steam dome 90, which collects the steam generated in the core 5 of the reactor pressure vessel 7’.
Also for the boiling water reactor 120, the safety condenser provides an additional heat sink for the reactor coolant, here the water in the primary circuit.
The reactor pressure vessel 7’ comprises a second outlet or outlet nozzle 128, which is connected to the safety condenser charge line 94. The second outlet 128 may be alternatively also connected to the first outlet 126. In other words, also in this embodiment the safety condenser charge line 94 is connected to the steam generating component 7’, in particular in form of the reactor pressure vessel. The second end of the heat exchanger 26, in particular via the return line 98, is connected to the reactor pressure vessel 7’, in particular above the reactor core 5.
Thus, the safety condenser 25 described here-above is connected to the steamgenerating component in a water-cooled nuclear reactor.in case of a boiling water reactor to the reactor pressure vessel 7’.
In principle, the safety condenser 25 and related components (the passive pressure pulse transmitter PPPT 102 for instance) as described here-above can also be installed at the steam generating component of a light-water cooled nuclear reactor using a watersteam cycle as driving medium for the turbine or as a heat sink for removing decay power.
In the case of a boiling water reactor for instance, where the reactor pressure vessel 7’ is directly producing steam, the steam generating component is the reactor pressure vessel 7’. Accordingly, for application in a boiling water reactor, the safety condenser 25 and the passive pressure pulse transmitter 102 together with its vertical pipe 118 are directly connected to the reactor pressure vessel 7’. Technical functionality and means to control and limit the heat removal capacity of the safety condenser 25 remain the same as for the application in a pressurized water reactor 3.
If the safety condenser 25 and the PPPT 102 are connected directly to the reactor pressure vessel 7’ of a boiling water reactor or other water cooled nuclear reactor (small modular reactor for instance), the fill level in the PPPT 102 and related vertical pipe 118 reflect the water level in the RPV 7’, see Figure 5. Both ends of the vertical pipe 1 18 are connected to the RPV 7’. If the water level in the reactor pressure vessel 7’ falls short of a certain level - which must be chosen in order to secure sufficient water coverage of the core at all times - the passive pressure pulse transmitter 102 activates the safety condenser 25 as described above by opening the return line cut-off valve 101 . The safety condenser 25 then acts as the ultimate heat sink for the steam source connected to the in and outlets of the safety condenser.
The steam source may also be a reactor pressure vessel of a light-water cooled nuclear reactor in general. The function to limit the heat removal capacity from the safety condenser 25 as described above may also be employed to limit the inflow of cold water to the reactor pressure vessel 7’or if a controlled cool-down and depressurisation is required.
It is contemplated that elements of one embodiment may be advantageously utilized in other embodiments without further recitation.
In some examples of implementation, any feature of any embodiment described herein may be used in combination with any feature of any other embodiment described herein.
List of reference signs:
1 Nuclear power plant
3 Pressurized water reactor
5 Reactor core
7, 7’ Reactor pressure vessel
10 Primary cooling circuit
12 Reactor coolant pump
14 Steam generator
16 Secondary cooling circuit
18 Turbine
20 Generator
22 Condenser
24 Condensate Pump
25 Safety condenser
26 Heat exchanger 28 Outlet
29 Downcomer section
30 Pool
31 Housing 32 Internal liner
34 Bottom
36 Covering
38 Opening
40 Opening 42 Side wall
44 Opening
46 Nominal water level
48 Area
50 Grid plate 52 Tubes
54 Upper end dome
56 Lower end dome
58 Upper tube sheet
60 Lower tube sheet 62 Support frame
63a Tube support plate
63b Tie rod
64 Flow skirt
66 Support frame 68 Skirt support
70 Outlet
72 Inlet
74 Sealing arrangement
76 Sealing support 78 Seal
80 Axial compensator
82 Shielding baffle
84 Support frame
86 Constant hanger 88 Drain pipe
90 Steam dome 92 Outlet pipe
94 Safety condenser charge line
96 Valve
98 Return line
100 Return line control valve
101 Return line cut-off valvel 02 Passive pressure pulse transmitter
106 PPPT primary chamber
107 PPPT secondary chamber
108 first, top nozzle to vertical pipe
110 second, bottom nozzle to vertical pipe
111 Wall
112 Blind tubes to heat secondary chamber
113 Filler tubes
114 PPPT secondary chamber, connection for refill,
116 PPPT secondary chamber, displacer body
118 Vertical pipe
120 Boiling water reactor
122 Recirculation pump
124 water-steam cycle line
126 Outlet
128 Outlet, outlet nozzle

Claims

1 Safety condenser (25) intended to be connected to a steam generating component (14, 7’) in a water-cooled nuclear reactor (3, 120) comprising:
- a heat exchanger (26) partially arranged in a pool (30) containing a cooling fluid, the heat exchanger (26) comprising a bundle of parallel heat exchanger tubes (52), the heat exchanger tubes extending in a vertical direction between a lower tube sheet (60) and a upper tube sheet (58), each heat exchanger tube (52) being intended for receiving a downward flow of steam from the steam generating component (14, 7’), the heat exchanger comprising an inlet (72), intended for receiving steam generated in the steam generating component^’, 14), the heat exchanger (26) being configured for cooling this steam through heat exchange with the cooling fluid contained in the pool (30) to produce condensate and an outlet (70), configured for returning the condensate to the steam generating component; and
- a cooling capacity regulator (100), configured for controlling the cooling capacity of the safety condenser (26) by adjusting the height of the condensate in the heat exchanger tubes, characterised in that the heat exchanger (26) further comprises a lower end dome (56) connected to the lower tube sheet (60) and comprising the outlet (70) intended to be connected to the steam generating component (7’, 14) and upper end dome (54) connected to the upper tube sheet (58) and comprising the inlet (72) intended to be connected to an outlet pipe (92) of the steam generating component (7’, 14), the lower end dome (56) and the upper end dome (54) being located outside of the pool (30).
2. Safety condenser according to claim 1 , wherein the lower end dome (56) and the upper end dome (54) have a semi-spherical shape.
3. Safety condenser according to claim 1 or 2, wherein the pool (30) is arranged in a housing (31 ), the housing having a first opening (38) in a covering (36) and a second opening (40) in the bottom (34), the first and second openings (38, 40) are vertically aligned to each other, wherein the heat exchanger extends through the first and second openings (38, 40).
4. Safety condenser according to claim 2, wherein the lower end dome (56) and the upper end dome (54) being located outside of the housing (31 ).
5. Safety condenser according to one of the preceding claims 3 or 4, wherein the lower tube sheet (60) is connected to a support frame (62) having a larger outer diameter than the diameter of the second opening (40), wherein in particular the support frame (62) has a smaller outer diameter than the diameter of the first opening (38).
6. Safety condenser according to one of the preceding claims 3 to 5, further comprising a sealing arrangement between the upper end dome (54) and the housing (31 ), wherein the sealing arrangement (74) comprises an axial compensator (80) enabling an axial movement along the longitudinal axis (X) of the heat exchanger (26) of the upper end of the heat exchanger (26) with respect to the housing (31 ).
7. Safety condenser according to claim 6, wherein a shielding baffle (82) is arranged spaced apart from the heat exchanger tubes (52) and/or the axial compensator (80).
8. Safety condenser according to claim 6 or 7, further comprising a sealing support (76), wherein the outer diameter of the sealing support (76) has a larger diameter than the first opening (38), wherein the axial compensator (80) is fixed to the sealing support (76).
9. Safety condenser according to claim 8, wherein the first opening (38) has a step shaped inner border and the sealing support (76) has a step shaped outer border being at least partially complementary to the steps of the inner border of the first opening.
10. Safety condenser according to one of the preceding claims, wherein the cooling capacity regulator (100, 101 ) comprises at least one valve (100, 101 ), in particular a plurality of valves being connected in parallel, wherein the at least one valve is arranged in a return line (98) between the outlet (70) and the steam generating component (7’, 14).
1 1 . Safety condenser according to one of the preceding claims, wherein the bundle of heat exchanger tubes (52) is at least partially surrounded by a flow skirt (64), wherein in particular the flow skirt covers at least 50 percent of the length of the bundle of heat exchanger tubes (52).
12. Safety condenser according to one of the preceding claims, wherein the heat exchanger tubes (52) are straight tubes.
13. Water-cooled nuclear reactor comprising a safety condenser according to one of the preceding claims.
14. Water-cooled nuclear reactor, wherein the steam generating component is a steam generator (14) of a pressurized water reactor or a reactor pressure vessel (7’) of a boiling water reactor.
15. Water-cooled nuclear reactor according to claim 13 or 14, further comprising a steam generating component (14, 90), wherein the inlet (72) of the heat exchanger is connected to an outlet pipe (92) of the steam generating component (7’ 14) and the outlet (70) of the heat exchanger (26) is connected to the steam generating component (7’ 14).
16. Water-cooled nuclear reactor according to one of the claims 13 to 15, further comprising a passive pressure pulse transmitter (102) adapted to emit a hydraulic pulse towards at least one of the return line valves (100) in case the water level in the steam generating component (7’, 14) falls below a predetermined level.
17. Water-cooled nuclear reactor according to one of the claims 13 to 16, wherein the nuclear reactor utilizes light water as primary cooling medium.
EP22822616.3A 2022-12-12 2022-12-12 Safety condenser and nuclear reactor containing the same Pending EP4634575A1 (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP2022/085450 WO2024125759A1 (en) 2022-12-12 2022-12-12 Safety condenser and nuclear reactor containing the same

Publications (1)

Publication Number Publication Date
EP4634575A1 true EP4634575A1 (en) 2025-10-22

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Application Number Title Priority Date Filing Date
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Country Status (4)

Country Link
EP (1) EP4634575A1 (en)
KR (1) KR20250109727A (en)
CN (1) CN120344802A (en)
WO (1) WO2024125759A1 (en)

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2584228B1 (en) 1985-07-01 1987-12-24 Framatome Sa EMERGENCY COOLING DEVICE WITH INTRINSIC SAFETY OF A PRESSURE WATER NUCLEAR REACTOR.
DE4126630A1 (en) 1991-08-12 1993-02-18 Siemens Ag SECOND-SIDED HEAT EXHAUST SYSTEM FOR PRESSURE WATER CORE REACTORS
DE4126629A1 (en) 1991-08-12 1993-03-11 Siemens Ag SECOND-SIDED HEAT EXHAUST SYSTEM FOR PRESSURE WATER CORE REACTORS
EP0704860B1 (en) * 1994-04-13 1999-12-29 FINMECCANICA S.p.A. AZIENDA ANSALDO A steam condenser with natural circulation for nuclear reactor protection systems

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WO2024125759A1 (en) 2024-06-20
CN120344802A (en) 2025-07-18

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