Patent Number: 052934136
Section: description

Referring now to the single FIGURE of the drawing in detail, there is seen a filter 2 disposed inside a containment 1 of a nuclear power plant. The filter 2 is provided for the purpose of filtering a gas-steam mixture that can be produced inside the containment 1 if a major malfunction should occur. In the event of such a malfunction, the release of considerable quantities of heat must be expected, which causes a large proportion of the water present inside the containment 1 to evaporate and causes the pressure inside the containment 1 to rise. When the calculated design pressure of the containment 1 is reached, the same gas-steam mixture is then released to the outside, while filtered by the filter 2, for pressure relief. The filter includes a container having a cylindrical middle part including outer and inner concentric walls 4 and 5 with lower ends being joined together by a curved base 8. The walls 4 and 5 have upper ends being joined together and closed off from the outside by a likewise curved cap 9. The walls 4 and 5 form an annular chamber 6, which surrounds an inner chamber 10. The first inner chamber 10 communicates with the second annular chamber 6 through openings located immediately below the cap 9. Inside the inner chamber 10, mist collectors 13 are secured to the upper end of the chamber 10, immediately in front of the openings in the wall 5. Filter mats 11 are disposed inside the upper half of the annular chamber 6. The filter mats 11 have a radially inner surface which communicates in a non-illustrated manner with the openings covered by the mist collectors 13 and a radially outer surface which communicates with another opening 18 leading outside, from which the filtered gas-steam mixture is carried out of the containment 1 through a pipe 19 penetrating the containment 1. The radially outer wall 4 is also pierced by an overpressure line 32, through which the annular chamber is relieved through the use of an overpressure valve 33, if an impermissibly high pressure should arise. In order to avoid convection over the entire height of the annular chamber 6, a perforated and/or slit convection barrier 12 is provided immediately below the filter mats 11. The inner chamber 10 is filled with a washing fluid 3 to an extent of 30 to 80%, and preferably approximately half, prior to initiation of operation of the filter 2. The annular chamber 6 between the walls 4 and 5 is filled virtually completely with heat-conducting fluid 7 below the convection barrier 12. In the exemplary embodiment, water is provided as both the washing fluid 3 and the heat-conducting fluid 7. The supply of the filter material, that is of the gas-steam mixture, into the filter 2 from the interior of the containment 1, is effected through a horizontal segment 15 that is located toward an upper end of a pipe 14 disposed vertically in the middle of the inner chamber 10. The pipe 14 has a lower end with horizontally extending feed pipes 16 disposed in a radial or star pattern, for short Venturi nozzles 17. Normally, and particularly during nuclear power plant operation according to plan, the horizontal segment 15 is blocked off from the interior of the containment 1 through both a check valve 22 located in a line 21, and a bursting disk 23. The interior of the filter 2 also communicates with a primary loop of the nuclear power plant in a non-illustrated manner. This communication is also blocked off during normal operation. During normal operation of the nuclear power plant, the pipe 19 originating at the opening 18 leading outside is also closed. This is effected by shutoff fixtures 25, which can uncover or unblock the pipe 19 so that it is open toward not only a throttle 28 but also a further bursting disk 26 and a chimney 27. A measuring filter 30 is provided parallel to the throttle 28 and to a further shutoff fixture 29 located between the throttle 29 and the bursting disk 26. A replenishment line 24 for washing fluid 3 communicates with the inner chamber 10 through the base 8. The replenishment line 24 penetrates the containment 1 and has a free end which is closed by shutoff fixtures 31 during normal operation. If a major malfunction occurs inside the containment 1, then as mentioned above a considerable proportion of the water present as coolant inside the containment 1 will evaporate, causing the pressure to rise inside the containment, which is immediately hermetically sealed off in gas-tight fashion from the outside when a malfunction occurs. Parallel to the evaporation of some of the water, a number of other reactions also occur, by means of which gases and/or vapors are also produced and/or released. As a result of all of these processes, the pressure prevailing inside the containment 1 sooner or later may reach the design pressure of the containment 1. This depends substantially on the quantity of heat released. However, the temperature inside the containment 1 also increases simultaneously with the pressure. As a result, the entire contents of the containment, thus including the filter 2 as well, are heated. The temperature of the contents of the containment 1 already reaches 100.degree. C. long before the calculated design pressure is approached. Since the interior of the filter 2 is sealed off hermetically from the outside and an inert gas cushion above the washing fluid is provided, the pressure inside the filter housing and the line elements connected to it rises as well, so that water provided as the heat-conducting fluid 7 and as the washing fluid 3 will not yet boil. Since heat transfer fins 20 are provided on the walls 4 and 5 in order to improve the heat transfer from the wall 4 to the heat-conducting fluid 7 and from the fluid to the wall 5, the amount of heat given up to the heat-conducting fluid 7 by the wall 4 is especially high, so that a containment vessel temperature of 150.degree. C., for example, is quickly reached. Accordingly, when the bursting disk 23 responds, the temperature of the washing fluid 3 is 150.degree. C., for example, which is the temperature that has been reached by then inside the containment 1. Thus the gas-steam mixture flowing through the line 21, the horizontal segment 15 and the pipe 14 and through the feed pipes 16 to the short Venturi nozzle 17, will be only insignificantly if at all warmer, than the washing fluid 3. Accordingly, when the gas-steam mixture mixes with the washing fluid 3 in the short Venturi nozzles 17, only an insignificant portion of the water steam will condense out of the gas-steam mixture, so that the gas-steam mixture emerging upward from the washing fluid 3 and also flowing out through the mist collectors or separators 13 and the filter mats 11 to the opening 18 leading to the outside substantially has the same composition as the mixture carried into the filter through the line 21. The gas-team mixture flowing into the filter 2 through the short Venturi nozzles 17 undergoes a pressure drop from 2000 to 200 hPa in this process, so that immediately after the response of the bursting disk 23, washing fluid 3 and heat-conducting fluid 7 evaporate. Since in contrast to the washing fluid, the heat-conducting fluid is not replenished, it is soon evaporated, and as a result the thermal bridge between the interior of the containment 1 and the interior of the filter 2 is broken. Due to the removal of the heat of evaporation, the temperature of the washing fluid 3 is approximately 10.degree. to 2.degree. lower than the temperature of the inflowing gas-steam mixture. After the response of the bursting disk 23, the pressure, which is lowered merely by the aforementioned amount, prevails in the filter 2. This pressure is almost equivalent to the pressure in the interior of the containment 1, so that only a relatively small volumetric flow of gas-steam mixture has to be filtered. Moreover, because of the accommodation of filter mats 11 in the chamber 6 annularly surrounding the inner chamber 10, a very compact, space-saving structure for the filter 2 is made possible. When the filter 2 is in operation for a relatively long period, filter material dripping out of the filter mats 11 will collect in the lower part of the chamber 6 and as a result will re-create a thermal bridge to the washing fluid 3. Nevertheless, this process proceeds so slowly that it presents no threat or substantial impairment to the filtration. In any case, during continuous operation of the filter, only relatively small losses of washing fluid need be expected, because only the quantity of heat contained in the filter material itself flows through the filter 2. However, as long as the partial pressure of the water steam in the gas-steam mixture is lower than the boiling pressure corresponding to the temperature of the washing fluid, some of the washing fluid will evaporate. As a result, heat is removed from the washing fluid, and in other words the temperature is lowered, until the boiling pressure is equal to the partial pressure.