Patent Number: 051223333
Section: description

Referring to FIG. 1, a water basin 2 having concrete walls 1 is largely filled with a bath of water and at the same time, acts as a storage basin for fuel elements rods of a nuclear reactor plant (not shown). A conduit 3 passes through one wall 1 of the basin 2 and extends, for example, to the interior of a containment or safety vessel of a nuclear reactor plant (not shown). This conduit 3 contains two containment isolating valves 4 between the containment vessel (not shown) and the basin 2 which open in the event of an excess pressure in the containment vessel. As illustrated, the conduit 3 extends vertically downwardly into the interior of the basin 2 and leads into a substantially horizontal distributor 5 from which a plurality of horizontal tubes 6 branch. For example, eight tubes as shown in FIG. 2, extend from the distributor 5. Each tube 6 is closed at the distal end, as shown to the right in FIG. 1. In addition eight vertical tubes 7 branch off from each horizontal tube 6 with each vertical tube 7 extending upwardly to a unit 8 consisting of a vertically disposed nozzle 9 and a baffle plate 10 (see FIG. 3). In all, there are sixty-four units 8 distributed over a rectangular area and all are disposed at the same height in a horizontal plane. A set 20 of static mixer elements 21 is provided above the sixty-four units 8 in the basin 2 and these elements 21 are completely submerged in the water filling the basin 2. The static mixer elements 21 are also circumferentially enclosed by a jacket 22, the bottom end of Which extends into the zone of the units 8. A conduit 23 is connected to the top 1' of the basin and leads to a venting chimney (not show) for the discharge of a flow of aerosol-depleted air therefrom. Referring to FIG. 3, each nozzle 9 of a unit 8 is formed of a vertical tube having a cross-section which tapers conically to some extent substantially in the middle of the tube length. The nozzle tube is also fixed at the bottom end to a cap nut 11, for example, by welding. This cap nut 11 has an opening 12 in line with the nozzle 9 in order to convey aerosol-laden air therethrough. In addition, the cap nut 11 has an internal screw thread 13 by means of which the cap nut can be threaded onto a vertical branch tube 7 which has a corresponding external screw thread. The baffle plate 10 is fixed on each cap nut 11 by means of three rods 14 which extend from the cap nut 11 in parallel and uniformally over the periphery of the cap nut 11. To this end, the cap nut 11 is provided with three axial recesses at the outer periphery to receive the bottom ends of the rods 14 which are then welded to the cap nut 11. The rods 14 pass through respective openings in the baffle plate 10 as indicated in FIG. 4 while pairs of nuts 15 are threaded on each rod 14 in order to secure the plate 10 therebetween at a precise location relative to the orifice of the nozzle 9. As indicated in FIG. 4, the baffle plate 10 is provided with a plurality of perforations 16. Any suitable distribution of perforations may be used. Each static mixer element 21 may, in known manner, be constructed of corrugated or fluted laminates, such as metal sheets. For example, referring to FIG. 5, each static mixer element 21 may be formed parallel Vertical sheets 31 having a plurality of parallel guide elements in the form of slats 32 welded to each sheet 31 and extending from opposite sides at a angle to the vertical. As indicated, the slats 32 on one sheet 31 are disposed in criss-crossing relation to the slats 32 connected to an adjacent sheet 31. In this respect, the static mixer elements 21 are built so as to form defined open intersecting flow passages between them. A detailed construction of such a mixer element is described, for example in Swiss patent 547,120. The apparatus described operates as follows. In the event of an excess pressure occurring in the containment vessel, e.g. due to a melt-down, the isolating valves 4 open. Aerosol-laden air from the containment vessel now flow via the conduit 3, tubes 6, 7 and nozzles 9 into the water bath of the basin 2. The air emerging from the nozzles 9 entrains water from the surroundings and mixes intensively on passage through the holes 16 in the baffle plates 10. The water-air mixture then flows on up and enters the static mixer elements 21. A continuous splitting up, elongation and re-arrangement of the components of the water-air mixture takes place in the intersecting flow passages of these mixer elements 21. The air rising from the nozzles 9 is divided up in each mixing element 21 into a number of sub-flows which cross one another at an angle of about 90.degree.. The mixing elements 21 are so stacked on one another in the set 20 that the vertical sheets 31 of one mixing element include an angle other than zero with those of the adjacent mixing element. In the embodiment of FIG. 1, this angle is, for example, 45.degree.. In these conditions, the air which entrains the aerosols is dispersed in the water. The aerosols are separated from the air to the water or to the mixer elements. Thus, air from which aerosols have been eliminated leaves the top end of the set 20 and then passes to the discharge chimney via the conduit 23 without having to pass through further filters. The water emerging at the top end of the set 20 circulates downwards outside the jacket 22, for which purpose sufficient space must be left between the walls 1 and the jacket 22. At the bottom end of the jacket 22, the water flows back into the area of the nozzles 9. Contrary to the embodiment described, instead of the arrangement of one baffle plate 10 to each nozzle 9, it is possible to provide a baffle plate common to all the nozzles or a common baffle plate for specific group of nozzles. The invention further provides an apparatus for eliminating aerosols from air escaping from a nuclear reactor containment vessel which is greatly reduced for at least a constant degree of purity of air leaving the apparatus relative to previously known apparatus. The invention further provides an apparatus for eliminating aerosols from air vented from a nuclear reactor pressure containment vessel in a relatively simple manner.