Patent Number: 041586034
Section: description

Referring now to the drawing and first, particularly, to FIG. 1 thereof, there is shown one condensation tube 1 forming part of a blow-off device for limiting excess pressure in nuclear power plants. Especially in a boiling-water nuclear power plant, a multiplicity of such condensation tubes 1 are disposed with the lower discharge ends 1a thereof immersed in a volume of water 2 received in a condensation chamber having a gas cushion 3 (such as an air space, especially) thereabove. Only one of such a condensation tube 1 is shown as an example of the multiplicity thereof in the blow-off device, the condensation tube 1 being connected at the upper inlet end thereof, as viewed in FIG. 1, which projects upwardly out of the water condensate 2, to a source of steam to be condensed or to a steam-air mixture. The illustrated condensation tube 1 is provided especially for blow-off devices of so-called pressure reduction systems for boiling-water reactors, the pressure reduction system being located within a safety vessel. It is the main objective of such a pressure reduction system, in the event of a coolant loss due to condensation of discharging steam-water mixture, to reduce the pressure rapidly. In this regard, as hereinaforementioned, a number of condensation tubes 1 are provided in the pressure reduction system which lead from a pressure chamber into the water condensate 2 of the condensation chamber. The water condensate 2 is thereby subcooled in accordance with the saturation pressure thereof. The equipment of the pressure reduction system are also advantageously employed for other purposes. Thus, the steam of the pressure-relieving and safety valves is conducted also through corresponding condensation tubes into the water condensate. Also, the exhaust steam of the emergency condensation and the emergency feed turbines are conducted expediently into the condensation chamber, since it is assumed that when these turbines are used, the main condenser is no longer available. It is important for the condensation process, that a very broad spectrum of possible steam flow densities exists. Thus, high steam flow densities are present in the case of the blow-off of the relief valves into the respective condensation tubes, and the same at the beginning of a coolant loss-disturbance. In contrast thereto, in the exhaust steam lines and the respective condensation tubes of the emergency condensation and the emergency feed turbines as well as in the course of a coolant loss-disturbance, the steam flow densities are low. The incident steam flow densities thus extend from about 1000 kg/m.sup.2 .times.sec during blow-off of the relief valve down to 2 to 10 kg/m.sup.2 .times.sec for steam vagabond flows. So that the steam flow and the bubbles produced in the volume of water become subdivided and a smooth condensation process is produced during blow-off, the discharge or outflowing end 1a of the condensation tube 1 is provided with wall parts 5 forming passages extending in axial direction, delimited from one another and terminating in the ater condensate 2. The wall portions 5 are constructed as a tube attachment R, which is mounted on the tube end 1b and has an opening 7 corresponding to the tube end 1b. The tube attachment R has a first group 5a of the wall parts 5 (FIGS. 2a and 2b) which are disposed in alignment with the tube end 1b, and furthermore a second group 5b of the wall parts 5 which surround the first group 5a of the wall parts and communicates laterally with the passages 4a thereof. The second group 5b of the wall parts 5 is, like the first group 5a of the wall parts 5, open at the lower end thereof, as viewed in FIG. 1. While the first group 5a of the wall parts forms, with the passages thereof opening upwardly to the inlet or inflowing end e1 thereof, a direct continuation of the flow channel formed through the condensation tube 1, the upper similarly open ends of the passages 4b formed by the second group 5b of the wall parts communicate with the water condensate 2. The wall parts-group 5a do not necessarily have to be open at the lower end thereof, as viewed in FIG. 1, if adequate flow-through cross-section from the first group 5a to the second group 5b is provided and adequate outlet cross section through the wall parts 5b is formed. As is apparent from FIG. 1, the second group 5b of the wall parts 5 overlaps the tube end 1b in axial direction. The tube attachment R, in vicinity of the opening 7 thereof, is provided with a tube section 8 having an inner diameter D.sub.r which corresponds to the outer diameter D.sub.1 of the condensation tube 1 so that, along the axial overlapping length 1, the tube attachment R is slid onto the condensation tube 1. A circular welding seam 9 is provided between the tube attachment R and the condensation tube 1 so as to affix them one to the other. The two embodiments shown in FIGS. 2a and 2b have first and second groups 5a and 5b, respectively, of the wall parts 5 with metal sheets or plates 10 extending in radial and axial directions of the tube attachment R, the metal sheets or plates 10 forming sector-shaped flow-through cross sections 4a and 4b. Whereas, in the embodiment of quadrant I as shown in FIG. 2b, the metal sheets or plates 10 extend from a central tube 11 to an outer jacket tube 12 and form sector-shaped through-passages 4 i.e. the wall parts 5a and 5b are united one with the other, in the embodiment of quadrants II and III as shown in FIG. 2a, in addition to the radially extending metal sheets or plates 10 in the annular space 13 of the second group 5b of the wall parts, a further subdivision by means of additional radially extending wall parts 10' is encountered. The passageway channels in the annular space 13 are therefore again subdivided. To hold these additional wall parts 10', divided rings 14 (note also FIG. 2d) are inserted into slots 15 formed in the metal sheets or plates 10. The ring halves of the rings 14 are provided, respectively, at the ends thereof with overlapping locations and are then welded into a continuous ring 14 (note the welding locations 14a in FIGS. 2a and 2b). Moreover, the metal sheets or plates 10 are connected, respectively, at the radially inner edge thereof to the central tube 11 and at the radially outer edge thereof to the jacket tube 12, preferably by welding. The additional wall parts 10' formed as intermediate metal sheets or plates are correspondingly welded at the radially inner edges thereof to the rings 14 and, similarly, at the radially outer edges thereof to the inner peripheral surface of the jacket tube 12. The embodiment of quadrant IV shown in FIG. 2c corresponds to that of FIG. 2a except that instead of the flat metal sheets or plates 10 and 10', serpentive metal sheets or plates 16 and 16' extending sinuously in radial direction are used, by means of which the wetting and cooling surfaces are able to be increased. Instead of having a serpentine waviness, the metal sheets or plates 16 and 16' may also be zig-zag-shaped. To brace or stiffen the tube attachment R, the main metal sheets or plates 10a to 10d disposed on a rectangular coordinate cross are increased in length in axial direction in accordance with the areas 17 and are welded to the tube or sleeve 8 that is slid onto the tube end 1b. The central tube 11, as illustrated, can be provided with a flow cone 11a, so that a flow-facilitating transition of the central steam jet or current to the passage cross section 5a occurs. This is especially indicated for full cross section of the central tube 11 which then forms a rod. The central tube 11 can, however, also have a hollow construction with a sharp rim so that a given fraction of the steam flow flows through the interior thereof. The course of the steam flow is indicated by arrows d and the course of the water fraction flowing in from the water condensate 2 is indicated by arrows w. Furthermore, a transition cone can be provided at the lower end of the central tube, as viewed in FIG. 1, which would then cover nearly the entire area 5a, so that a transition to the surface area of the wall parts 5b would occur and a lengthening of the wetting and cooling lengths may be imparted thereto. The two additional embodiments of the invention shown in FIGS. 3, 4a and 4b have in common that the first group 5a of the wall parts 5 is surrounded by a tube 18 that is slidable onto the tube end 1b, the tube 18 having an inner diameter D.sub.18, as mentioned hereinbefore with respect to the tube attachment-sleeve 8 according to FIG. 1, corresponding to the outer diameter D.sub.1 of the condensation tube 1, so that this tube 18 is also slidable onto the condensation tube 1 i.e. the tube end 1b thereof. This slide-on tube 18 extends, however, through to the lower end of the tube attachment R, as viewed in FIG. 3, so that the second group 5b of the wall parts (annular space 13) surrounds the inner tube 18 along the entire axial length thereof, and also the entire axial length is available for fastening purposes. In order that the passages 4b will communicate with the passages 4a, the inner tube 18 is formed with openings 19 over the entire surface thereof, the openings 19 being in the form of slots disposed in rows 19a in the illustrated embodiment of FIG. 3. For reasons of strength, the slot rows 19 adjacent one another in peripheral direction are offset by half a slot-length from one another. In addition, like parts in the various embodiments shown in FIGS. 1, 2a, 2b, 2c and 3 are identified by the same reference characters. The embodiment of the invention in quadrant IV shown in FIG. 4b is modified with respect to the embodiment shown in FIG. 4a in that the first group 5a of the wall parts 5 is formed of wave-shaped metal sheets or plates 20 which, in contrast to the serpentive metal sheets or plates 16 of FIG. 2c, are not radially oriented but rather have a chord-like orientation. Through the slot openings 19 of the inner tube 18, the passages 4a between the metal sheets or plates 20 are also, in the embodiment of FIG. 4b, connected flow-wise with the passages 4b between the radially oriented metal sheets or plates 21 of the second group 5b of wall parts. A subdivision of the steam blows and of the bubbles that are formed occurs also with this embodiment of the invention, as well as also a fanning out of the steam flow or the steam-air-water mixture discharging from the tube end 1b to the larger passage cross section, which is formed by the tube attachment inner sleeve 18. The operation of the embodiments of FIGS. 3, 4a and 4b, as illustrated by the arrows d and w in FIG. 3, corresponds to the operation of the first three embodiments of the invention shown in FIGS. 1, 2a, 2b, 2c and 2d.