Patent Number: 042657075
Section: description

DETAILED DESCRIPTION As shown in the drawings, the apparatus for carrying out the process of the invention comprises a dust container 1 of the hopper type, having its outlet 2 leading into a pneumatic feed line 3. One end of the feed line 3 is connected to equipment for supplying gas under pressure that includes a reducing valve 4 for setting the gas pressure in the feed line and, also, a compressed gas storage tank 5 which can be filled with compressed gas after opening of a gate cock 6 between the tank 5 and a compressor 7. In the illustrated example, air is used as the compressed gas. It is also possible, however, to connect gas storage tanks filled with inert gas, especially nitrogen tanks, to the suction pipe 8 of the compressor 7, for use in order to prevent dust explosions when combustible dusting powder is used. In the illustrated example, fire estinguishing powders are stored in the dust hopper 1, such materials having very little danger of explosion. The equipment for supplying compressed gas is installed outside the reactor building. In FIGS. 1 and 2, the illustration of the reactor building itself is limited merely to a portion of the outer pre-stressed concrete wall structure 9 having a liner 10 provided on its internal side. Within the reactor building, there is located a gas-cooled high-temperature nuclear reactor that is not shown in the drawing. The pneumatic feed line 3 leads through the pre-stressed concrete wall structure 9 and ends in the internal space 11 of the reactor building. At this end of the feed line 3, a dust dispersion nozzle 12 is provided through which the dusting material, carried through the feed line 3 by compressed gas, issues in fine dispersion into the internal space. The gas pressure in the feed line 3 is set at a value that depends on the pressure in the internal space 11. For this purpose, the pressure reduction valve 4 is in operative connection with a pressure-sensing box or enclosure 13 located in the internal space 11. In order to prevent or mitigate undersired effects of overpressure occurring in the internal space of the reactor building, particularly pressure shocks produced by the contingency in question, on the pneumatic feed line 3 and the dust hopper 1, a check valve 14 is inserted in the feed line downstream, in the direction of feed, of the outlet 2 of the dust hopper. The orifice of the outlet 2 of the dust hopper 1 in the feed line 3 is conventiently constituted as a tube opening out in the feed direction, so that the dusting powder stored in the hopper 1 can be drawn out by the gas flowing in the feed line 3, completely and without disturbance. In order to make it possible to introduce additional quantities of dusting powder, beyond the amount left over from the last charge, at any particular time, and to furnish the same to the space within the reactor building, an input device 15 is provided at the top of the dusting powder hopper container 1. In the illustrated example, the dusting powder hopper 1 is conveniently located outside of the reactor building. The dusting powder hopper can, however, also be provided inside the reactor building. FIG. 2, which is a bottom view of the equipment shown in FIG. 1, shows that the equipment 5,6,7,8 for supplying compressed gas feeds a number of feed pipes 3a, 3b, 3c connected in parallel. In the illustrated example, only three branches are shown but, of course, a branching manifold could be provided taking care of many more such parallel feed lines. Each of the feed lines 3a, 3b, 3c is connected with an individual dusting powder hopper 1a, 1b, 1c. Each feed pipe leads into the internal space 11 of the reactor building and there is at least one dust dispersion nozzle, and generally more than one. Thus, the powder hopper 1b feeds power into the line 3b which is sprayed out by the nozzles 12' and 12" shown in FIG. 2 and others not shown in the drawing. The provision of several independent systems, each with its own supply hopper for the dust or powder particles, for introducing the particles into the internal reactor space is, of course, an advantage from the point of view of security and reliability. The distribution of the dusting nozzles 12' 12" over the ceiling surface 16 in the internal space 11 of the reactor building is illustrated in FIG. 2. The spacing between the dusting nozzles 12' and 12" as well as between these and the adjacent dusting nozzles on the adjacent feed lines is determined with regard to magnitude of the dusting radius provided for the dusting powder particles, in such a way that a distribution of the dust particles that is to a great extent homogeneous is produced in the gas atmosphere in the internal space of the reactor building. The amount of dust or powder to be blown into that space is determined by the desired reaction of the content of fission and activation products after dusting of the gas atmosphere by blowing in the dust particles. FIG. 3 shows that at least 500 kg of dusting particles of an average grain size d'=0.5 .mu.m should be injected for 50.10.sup.3 m.sup.3 of volume of the enclosed gas atmosphere, in order to knock down the content of fission and activation products from 1% to 1.multidot.10.sup.-4 % within a period of 100 hours. Shorter periods for the reduction of the fission and activation products in the gas atmosphere can be obtained by dispensing larger quantities of dusting powder. If 40 tons of dusting particles of the same average grain size d'=0.5 .mu.m are introduced in a space having a volume of 50.multidot.10.sup.3 m.sup.3, the content of fission and activation products falls from 1% of to a value of 1.multidot.10.sup.-4 % after only approximately one hour. Although the invention has been described with reference to a particular illustrative example, it will be understood that modifications and variations are possible within the inventive concept.