Patent Number: 052727335
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 represents a control rod driving hydraulic system relating to a first embodiment. The embodiment comprises replacing the driving water filters 6 installed on an outlet side of the driving water pump 4 shown in FIG. 8 as a prior art with hollow fiber filter units 28. Referring to FIG. 1, during operation of a nuclear power plant, water coming from the condensate demineralizer 3 passes the suction filter 5, and after being pressurized by the driving water pump 4, it passes the hollow fiber filter unit 28, and is partly supplied to the control rod driving mechanism 1 by way of the flow control valve 8 and the pressure control valve 10. Here, foreign materials such as cladding and others which are mixed into the driving water are removed first from passing the suction filter 5. However, a minute insoluble solid material of about 25 .mu.m or below in size cannot be removed through the suction filter 5 and thus comes into the driving water pump 4, and is discharged to the hollow fiber filter unit 28, and the solid material is removed almost perfectly. Accordingly, the driving water which comes out of the hollow fiber filter unit 28 becomes pure and free from foreign materials therein. Thus, an abnormity of extra ordinary operation of the control rod driving mechanism 1 due to biting of foreign materials in the driving water is prevented from arising to maintain a stable driving performance. In the case of the prior art exemplified in FIG. 8, when equipment is disassembled for plant construction and periodical survey or inspection and a water source is changed from the condensate demineralizer 3 to the condensate storage tank 18, a work for withdrawing the air must be carried out with great care, however, since the hollow fiber filter unit 28 is installed on an outlet (discharge) side of the driving water pump 4 of the control rod driving hydraulic supply system in the embodiment, the air is collected through the hollow fiber filter unit 28. Thus, the aforementioned vent ,work can sharply be cut down and simplified as well, and therefore a time consuming construction process and a periodical survey process can be reduced, thereby realizing an economical management. FIG. 2 represents a second embodiment of the control rod driving hydraulic system relating to the present invention, and this embodiment comprises replacing the suction filters 5 provided on an inlet side of the driving water pump 4 in the case of prior art exemplified in FIG. 8 with the hollow fiber filter units 28. The remaining construction is not different from that of FIG. 8, Therefore a further description will be omitted here. A driving water from the condensate demineralizer 3 passes the hollow fiber filter unit 28 before entering the driving water pump 4, foreign materials being removed therethrough. Since the driving water having the foreign materials removed as above comes into the driving water pump 4 in this case, a performance of each equipment can be maintained as preventing the biting of the foreign materials to the driving water pump 4. The hollow fiber filter unit 28 collects the air as in the case of control rod driving device given in the first embodiment, therefore the air generated on an upstream side of the hollow fiber filter unit 28 is prevented from flowing into the piping, the control rod driving mechanism 1 and the water pressure control unit 2, and the vent work for withdrawing the air can sharply be cut to realize an economical management. In the above embodiments, the two driving water filters 6 and the two suction filters 5 are substituted with two hollow fiber filter units 28, respectively, only ones of them 6 and 5 may be substituted with the filter unit 28. FIG. 3 represents a control rod driving hydraulic system relating to a third embodiment according to the present invention, in which like reference numerals are added to elements or unit corresponding to those of the first and second embodiments and in which one of the driving water filters 6 in FIG. 8 installed on an outlet side of the driving water pump 4 is substituted with a hollow fiber filter 28. The other one of the filters 6 is of a conventional knotting-wire type filter. As shown in FIG. 4, a hollow fiber filter unit 28 is provided with a sealing casing 28a which is divided into upper and lower sections by a partition plate 28b provided with a number of perforations. Filter elements 28c each is composed of a number of hollow fibers each passing the perforation of the partition plate 28b. The driving water fed into a lower filtering chamber 28d of the sealing casing 28a is filtered by the filament elements 28c, and thereafter, the driving water is drained to an outlet unit 28h via an upper header chamber 28e and a drain pipe 28g provided with an open/close valve 28f. An inlet pipe 29a is connected to the driving water filter unit 28 so as to feed the driving water from the inlet unit 29, and a flow meter 29b and an open/close valve 29c are provided for the inlet pipe 29a. A differential monometer 29d is provided for a duct connecting the inlet pipe 29a and the drain pipe 28q. In this embodiment, water coming from the condensate storage tank 18 passes the suction filter 5 and after being pressurized by the driving water pump 4, it passes the hollow fiber filter unit 28 via the inlet pipe 29a and then, through the drain pipe 28g, is partly supplied to the control rod driving mechanism 1 by way of the flow control valve 8 and the pressure control valve 10. Here, foreign materials such as cladding and others which are mixed into the driving water is removed first from passing the suction filter 5. However, a minute insoluble solid material of about 25 .mu.m or below in size cannot be removed through the suction filter 5 and thus comes into the driving water pump 4, and is discharged to the hollow fiber filter unit 28 from the pump 4. A cladding of about 0.1 .mu.m or so is picked up through the hollow fiber filter unit 28 and the solid material is removed almost perfectly. Accordingly, the driving water which comes out of the hollow fiber filter unit 28 becomes pure free from foreign materials therein. Thus, an abnormity of extra ordinary operation of the control rod driving mechanism 1 due to the biting of the foreign materials in the driving water is prevented from arising to maintain a stable driving performance. The purge water for the mechanical seal of the reactor coolant recirculation pump 30 is branched from the control rod driving water system, so that when the control rod driving water is made clean, the purge water for the mechanical seal of the recirculation pump 30 can be also cleaned simultaneously. Accordingly, the biting of the foreign materials to the mechanical seal can be substantially prevented, thus reducing the leakage of water. In the case of the prior art exemplified in FIG. 8, when equipment is dissembled for plant construction and periodical survey or inspection and a water source is changed from the condensate demineralizer 3 to the condensate storage tank 18, a work for withdrawing the air must be carried out with great care, however, since the hollow fiber filter unit 28 is installed on an outlet (discharge) side of the driving water pump 4 of the control rod driving hydraulic supply system in the embodiment, the air is collected through the hollow fiber filter unit 28. Thus, the aforementioned vent work can sharply be cut down and simplified as well, loads of a construction process and a periodical survey or inspection process can be reduced, thereby realizing an economical management. The backwash regeneration equipment for the hollow fiber filter unit 28 will be described hereunder with reference to FIG. 4. Referring to FIG. 4, the backwash regeneration equipment 31 is provided with an air supply tube 33 led from an air inlet 32, and the air supply tube 33 is branched into two branch tubes on the way thereof, one being communicated with the header chamber 28e of the sealing casing 28 as an air purge duct 34 and the other being communicated with the filtering chamber 28d as a bubble supply duct, 35. The filtering chamber 28d is provided with a perforated bubble generation member 36, composed of a perforated tube, connected to the bubble duct 35. The air supply tube 33 is equipped with an open/close valve 37 and an air filter 38, and the air purge duct 34 and the bubble supply duct 35 are also equipped with open/close valves 39 and 40, respectively. A plurality, three, for example, of drain pipes 41, 42 and 43 are connected to the filtering chamber 28d of the hollow fiber filter unit 28 to portions of different levels, and these drain pipes 41, 42 and 43 are connected to a radioactive waste disposal unit 48 through open/close valves 44, 45, 46 and 47. In the hollow fiber filter unit 28 of the characters described above, during the water supply through the condensate storage tank 18, the quantity of the cladding caught by the fiber filament element 28c is gradually increased. This fact of increasing of the quantity of the cladding caught can be confirmed by the supply water quantity measurement by the flowmeter 29b and the pressure difference measurement by the differential manometer 29d between the inlet pipe 29a and the drain pipe 28g. When these measurement values reach predetermined reference values, it is discriminated that the washing of the hollow fiber filter unit 28 should be made. At the washing time of the hollow fiber filter unit 28, the driving water supply pump 4 first stops and the open/close valves 29c and 28f of the inlet pipe 29a and the drain pipe 28g are closed. In the next stage, the open/close valves 44 and 47, which are disposed for the drain pipes 41 and 43 disposed to high level positions of the hollow fiber filter unit 28, are made open thereby to drain the water in the unit 28 so that the water level therein is lowered below the partition plate 28b. In this operation, the open/close valves 37 and 39 of the air supply pipe 33 and the air purge duct 34 are made open and the pressurized air is supplied from the air inlet 32 to an upper portion of the sealing casing 28a of the hollow fiber filter unit 28, thus draining smoothly. The supply of the pressurized air makes swollen the filter elements 28c. Under this condition, the open/close valve 40 of the bubble supply duct 35 made open and the bubbling operation is performed in the filtering chamber 28d by the air supply to the bubble generation member 36. According to this bubbling, the cladding adhering on the outer surface of the filter elements 28c is removed, thus performing the backwash regeneration treatment. After the removal of the cladding by the bubbling for a predetermined time, the open/close valves 45 and 46 of the drain tube 42 are opened and the water in the filtering chamber 28d is drained into the radioactive waste disposal equipment 48. Thereafter, the valves opened for the backwash operation are closed and the valves such as the valve 29c opened during the backwash operation are then closed. The filtering operation of the driving water is then again carried out. According to this embodiment, the frequencies of the exchanging of the filter elements 28c of the hollow fiber filter unit 28 can be significantly reduced by this backwash regeneration process and the quantity of the secondary radioactive waste can be hence reduced. In addition, since it is possible to regenerate the filter elements 28c, it is not necessary to limit the water source to the condensate subjected to the demineralizing process carried out by the condensate demineralizing unit. In the meantime, according to this embodiment, one conventional knotting-wire type filter unit 6 and one hollow fiber filter unit 28 are arranged in parallel for two control rod driving water filters. Since it is necessary for the hollow fiber filter unit 28 to be periodically exchanged with the other one, the knotting-wire type filter unit 6 is used at a time of exchanging the hollow fiber filter unit 28, whereas the hollow fiber filter unit 28 is utilized at a time other than exchanging time. Namely, the cladding adheres to the hollow fiber filter even if the filter is not used for the actual driving water filtering operation, and accordingly, it is necessary to periodically exchange the hollow fiber filter even if not used, resulting in the troublesome workings and demerit in economy as well as increasing of the waste. On the other hand, the knotting-wire type filter can be used for a long time and only a short time is required for the exchanging of the hollow fiber filter. Based on the above technical facts, according to this embodiment, since the conventional knotting-wire type filter is utilized only at a time of the exchanging of the hollow filler filter, the generation of the waste can be reduced and the working of the operator can also be reduced as well as the economical merit. The arrangement of the two types of filters may prevent, reduce the simultaneous operation function problem of two filters in comparison with the usage of the same type. A fourth embodiment according to the present invention will be described hereunder with reference to FIG. 5, in which like reference numerals are added to elements or parts corresponding to the aforementioned embodiments and the description thereof is made simple or omitted. In the embodiment of FIG. 5, one of the suction filters 5 disposed on the inlet side of the driving water pump 4 shown in FIG. 8 is substituted with a hollow fiber filter unit 28. The driving water from the condensate demineralizer 3 passes the hollow fiber filter unit 28 just before the entrance into the driving water pump 4 to thereby remove foreign materials. According to this construction or arrangement, substantially the same effects and functions as those attained by the third embodiment can be achieved. In this embodiment, furthermore, since the driving water after the removal of the foreign materials enters the driving water pump 4, the biting of the foreign materials in the driving water pump 4 can be prevented, thus effectively maintaining the performance of the other elements or parts. A fifth embodiment according to the present invention will be described hereunder with reference to FIG. 6, in which like reference numerals are added to elements or parts corresponding to the aforementioned embodiments and the description thereof is made simple or omitted. In a case where only one suction filter 5 is disposed, the embodiment of FIG. 6 represents a case in which this one suction filter 5 disposed on the inlet side of the driving water pump 4 is substituted with a hollow fiber filter unit 28, and accordingly, in this embodiment, no suction filter is arranged. It is to be noted that according to this fifth embodiment substantially the same effects and functions as those attained by the former embodiment can be achieved. In the foregoing disclosures, the embodiments represented by FIGS. 3, 5 and 6 are mentioned with reference to FIG. 4, it is to be easily understood that the hollow fiber filter unit of FIG. 4 may be applicable to the embodiments of FIGS. 1 and 2 with minor but not substantial modification. It is also to be understood by persons in this art that the present invention is not limited to the described embodiments and other changes or modifications may be within the scope of the appended claims.