Patent Number: 056595913
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in detail to the figures of the drawings, which are sometimes simplified, and first, particularly, to FIG. 2 thereof, there is seen a longitudinal section through a reactor building of a pressurized water reactor in an axis of a fuel assembly storage trough LB, which includes an outer storage trough LB1 and an inner storage trough LB2. A central reactor pressure vessel 1 outputs nuclear heat energy it produces through non-illustrated steam generators, which in turn supply fresh-steam lines 3. Reference numeral 2 indicates a pressure holder through which pressure can be kept constant in the primary system. The reactor pressure vessel 1, the pressure holder 2, the non-illustrated steam generators, an immersion pump TP with the inner storage trough LB2 surrounding it as well as the outer storage trough LB1, are disposed inside a spherical safety tank 4 made of steel which may have a diameter of 56 m, for example. Everything that is located inside of this safety tank 4 is referred to as a containment C. The safety tank 4 is surrounded by a secondary shield 5 of concrete. A concrete foundation 6 acts through a spherical shell 7 to support a lower region of the safety tank 4. An annular chamber RR which is located between the secondary shield 5 and the safety tank 4, is kept at a slight negative pressure for safety reasons (monitoring for tightness, i.e. the absence of leaks). The secondary shield 5, the concrete foundation 6, the spherical shell 7 and other walls shown in FIG. 2 taken together, are referred to as a concrete building or reactor building 8. The outer and inner storage troughs LB1, LB2 are filled with borated water 9 approximately up to the level shown. A compact storage system 10 for fuel assemblies is located in the storage trough LB1, and a fuel assembly changing machine 11 is positioned above the storage trough LB1. In the event of a fuel assembly change, fuel assemblies can be taken out of or inserted into the compact storage system 10 through the use of the fuel assembly changing machine 11. In this process of fuel assembly changing, a covering 12 of the inner storage trough LB2 is partially removed, and the fuel assembly changing machine can be moved crosswise up to a position above the opened reactor pressure vessel 1 with the fuel assembly suspended from the fuel assembly changing machine, through the use of removable protectors (portions of an intermediate wall 13 and a wall 14). A chamber 15 above the reactor pressure vessel 1 is likewise filled with borated water 9. During normal operation of the nuclear reactor plant, the inner trough LB2 serves as a water reservoir for borated water 9, so that in the event of an incident there is sufficient water on hand for a containment spray system CS seen in FIG. 1. Except for a somewhat different course of the outer wall 14, FIG. 1 shows an enlarged portion of the outer and inner storage troughs LB1, LB2. One can see that the inner storage trough LB2 is a water trough, to which a spray branch 16 with a spray head 17 and spray nozzles 18 is connected, and that the immersion pump TP is a pump which is provided for injecting water into the containment C seen in FIG. 2 in finely dispersed form in the event of an operational incident. In the example shown the immersion pump TP is supported on a bottom 19 of the trough LB2. The immersion pump TP aspirates the water 9 from the trough LB2 through a diagrammatically illustrated filter 20, pumps it through a riser pipe 21 into a remaining portion of the lines in the spray branch 16, which are represented partially in suggested fashion by dashed lines, and from there through the nozzles 18 of the spray head 17 or spray nozzle array into the containment C in the finely dispersed form of a spray mist. Since both troughs LB1 and LB2 are virtually completely filled with borated water 9, as is indicated by a water surface 22, adequate spray water is available in the event that emergency cooling is needed. Up to a certain extent, the water 9 of the outer storage trough LB1 can also be utilized for spray purposes. In other words, the fuel assembly storage system 10 must remain covered with trough water. The sprayed trough water, which serves the purpose of aerosol formation, cooling of the containment, and pressure reduction, condenses for the most part and passes from the walls of the containment for the most part into a reactor sump (not shown in FIG. 2) and can still be used as sump water for emergency cooling and aftercooling purposes. However, in that case it is no longer used for spraying. The water reservoir of the inner storage trough LB2 can be replenished if needed through the use of a non-illustrated supply trough located at a higher level, so that long-lasting spray operation can be maintained. A so-called centrifugal mist nozzle shown in FIG. 3 serves the purpose of fine atomization of liquids, in the present case borated water. It may be ordered as Model 121 from the company Schlick-Dusen, AlexandrinenstraBe 9, D-96450 Coburg, Germany. It is a three-part nozzle, including a nozzle head d1, a swirl insert d2 and a screw-in part d3 with a male thread. The nozzle head d1 has a nozzle bore 23, is shaped hemispherically and has a hexagon 24. A portion of the swirl insert d2 that protrudes axially outward is surrounded by a hollow-cylindrical screen body 25, by way of which the pressurized water can enter radial channels 26 and from there can enter an axial channel 27. Channels 28 discharging on an innermost end of the swirl insert from the axial channel 27 into an annular chamber 29 are shaped in such a way that a rotating ring of water develops in the annular chamber 29, which communicates through a gap 30 with the nozzle bore 23. In this way, the water that is under pressure is atomized into superfine droplets with a large specific surface area. The water is supplied under pressure to the nozzle 18 and passes through the chamber or tangential slits 29 into the gap or circulating chamber 30. In this case, pressure energy is converted into rotational or motion energy. A rotating film of liquid forms around an air core and emerges in the form of a hollow-conical stream through the orifice bore 23 and breaks apart into many small droplets, after surface tension has been overcome. The quality of atomization and the droplet range are dependent on a bore diameter D, the magnitude of the atomization pressure, the scattering cone, the viscosity, the surface tension and the density. A suitable plurality of the nozzles 18 of FIG. 3 are screwed by their screw-in parts d3 into a nozzle head of the kind that can be diagrammatically seen in FIG. 1. FIG. 4 shows a family of characteristic curves for the Model 121-type nozzle shown in FIG. 3. The curves represented by solid lines are preferred operating states and those shown as dashed lines represent further possible operating states. It can be seen that as the bore diameter D which is shown in millimeters increases, the feed pressure of the pump must Likewise become greater, so that a preferred droplet size L of less than or equal to 100 .mu.m can be achieved. Thus for a nozzle bore diameter in the range between 0.5 mm and 1 mm, the feed pressure of the pump is between about 3 bar and 80 bar. By comparison, in the case of a nozzle bore diameter D that is larger and in the range between 1 mm and 1.5 mm, the feed pressure of the pump is preferably between about 6 bar and 80 bar. At 50 bar and a bore diameter of 1 mm, very fine drops are obtained with a droplet size of approximately 50 .mu.m. Examples of possible materials for the nozzle 18 are brass, acid-proof special steel, heat-resistant special steel, titanium and tantalum.