Patent Number: 047770082
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, a water chamber isolating device (50) according to one preferred embodiment of the present invention will be described in more detail with reference to FIGS. 1 to 7. In FIG. 1, a water chamber (1) communicated with a nuclear reactor vessel via coolant piping communicates with a nozzle section (2) of the coolant piping, and at a manhole (25) communicating with the water chamber (1) is formed a mount seat (3) for a cover (not shown). A plug (4) disposed within the nozzle section (2) consists of a circular plate shaped seal lid (5), a hold plate (6), a mount plate (7) and the like, and it occupies a principal portion of the water chamber isolating device (50). A rigid support frame comprising a rigid support arm (8) has its one end detachably secured to the mount seat (3) at the manhole (25) by means of bolts (9) and the other end engaged with an inner wall surface of the nozzle section (2). An attitude of the plug (4) is held in a favorable manner by means of an angle adjusting screw (10) comprising a threaded support rod interposed between the support arm (8) and the mount plate (7). The seal lid (5) has a diameter greater than that of the manhole but is formed of a lid member and hinges (11), the lid member being foldable in three rigid plate-shaped pieces at hinges (11) as shown in FIG. 2(a) (by dash lines) and in FIG. 2(b) (by dash-dot lines) in order that it can be brought into the water chamber (1) through the manhole (25), and onto the bottom and top surfaces of the seal lid (5) are attached rubber seal plates (12) and (13), respectively. In addition, four stud bolts (14) for integrally fastening the hold plate (6) and the mount plate (7) are fixedly secured to the seal lid (5). The hold plate (6), also having a diameter greater than that of the manhole, is divided into two pieces as shown in FIGS. 3(a) and 3(b) in order that it can be brought into the water chamber (1) through the manhole (25) which is smaller than (has a diameter smaller than that of) the nozzle section (2), and it is provided with mushroom-shaped bolt-holes (15) through which the stud bolts (14) penetrate, in order to facilitate positioning of the hold plate (6). The mount plate (7) is provided with brackets (16) projecting from its top surface at its one end as shown in FIGS. 4(a) and 4(b), and these brackets (16) are pivotably engaged with a pin (17) which is in turn pivotably engaged with brackets (18) projecting from the bottom surface of the support arm (8) at its one end. In addition, in a seat (19) fixedly secured to a central portion of the top surface of the mount plate (7) is fitted a sphere (20) provided at the bottom end of the angle adjusting screw (10) so as to be able to perform a precession motion. The angle adjusting screw (10) is threadedly mated with a threaded hole (22) in a cylindrical pin (21) that is slidably and rotatably supported by the support arm (8) and extends through the hole (22), and a rectangular surface (23) is formed at the top end of the angle adjusting screw (10). In the mount plate (7) are also formed mushroom-shaped bolt-holes (24) through which the stud bolts (14) penetrate, in order to facilitate positioning of the mount plate (7). Then, under the condition that water has been extracted from the coolant circulating loop including the steam generator and the manhole (25) has been opened, the water chamber isolating device (50) is mounted. More particularly, after the seal lid (5) has been folded in three pieces and thus brought into the water chamber (1) through the manhole (25), it is again extended into a plate shape within the water chamber (1). Subsequently, the hold plate (6) is brought into the water chamber (1) through the manhole (25) as divided into two pieces. Furthermore, the mount plate (7) and the support arm (8) are brought into the water chamber (1) through the manhole (25) in the assembled state as shown in FIGS. 4(a) and 4(b). Then the hold plate (6) is superposed on the seal lid (5), further the mount plate (7) is superposed thereon with the stud bolts (14) penetrated through the mushroom-shaped bolt-holes (15) and (24) to effect positioning, nuts (26a) are threadedly engaged with the top ends of the stud bolts (14) and fastened, and thereby the plug (4) is assembled. Next, if the angle adjusting screw (10) is rotated by engaging a spanner or the like with the rectangular surface (23) formed at the top end of the screw (10), then the plug (4) is rotated about the pin (17) and forms a predetermined angle with respect to the support arm (8). Then, the plug (4) is inserted into the nozzle section (2), and under the condition that the tip end of the support arm (8) is engaged with the inner wall surface of the nozzle section (2), the base end of the support arm (8) is fixedly secured to the mount seat (3) at the manhole (25) by means of the bolts (9). In this way, blocking of the nozzle section (2) by means of the plug (4) is completed. It is to be noted that the seal lid (5) could be modified in such manner that it is divided into two pieces as shown in FIGS. 5(a) and 5(b) and the two pieces are connected by the rubber plate (12) secured to their bottom surfaces so as to be folded in two pieces as shown by dash-dot lines. Moreover, as shown in FIG. 6, the hold plate (6) could be omitted. Thus, when the blocking of the nozzle section (2) by the plug (4) has been completed, water is poured into the nuclear reactor cavity (05). Then, the water reaches the nozzle section (2) through the coolant piping (04), a hydraulic pressure of about 1 kg/cm.sup.2 is exerted upon the bottom surface of the plug (4), hence the rubber plate (12) attached to the bottom surface of the seal lid (5) is brought into press-contact with the inner wall surface of the nozzle section (2) to seal the plug (4), and at the same time, the force applied to the plug (4) by this hydraulic pressure is borne by the inner wall surface of the nozzle section (2) via the tip end of the support arm (8). In this way, the steam generator can be isolated from the other primary cooling systems, so that under this condition, inspection of the thin tubes in the steam generator can be carried out as by means of a robot or the like, and simultaneously with this thin tube inspection, routine inspection tasks relating to the nuclear reactor can be effected. In order to prevent leakage water from flowing out of the water chamber (1) in the event that water should leak through the plug (4) provided in the nozzle section (2), the manhole (25) is closed by a cover (26) as shown in FIGS. 7(a) and 7(b). The cover (26) is connected to a seat plate (28) so as to be swingable about a hinge (27), and the seat plate (28) is fastened to the mount seat (3) at the manhole (25) by means of bolts (29) and nuts (30). By rotating levers (31) in the direction of arrows, which levers are mounted so as to be rotatable about the bolts (29), the tip ends of the levers (31) are brought into contact with the outwardly convexed outer surface of the cover (26), and hence the cover (26) is brought into tight contact with the seat plate (28). Reference numeral (32) designates a handle provided on the outer surface of the cover (26), numeral (33) designates a robot for inspection and repair of the thin tubes in the steam generator, numeral (34) designates a cable for controlling the robot (33), which cable extends externally through a seal (35) provided at the center of the cover (26). Upon inspection and repair of the thin tubes in the steam generator, the manhole (25) is opened while the cover (26) is kept in the state shown by dash-dot lines in FIG. 7(a), but in the event that water should leak through the plug (4), the manhole (25) is closed by rotating the cover (26) about the hinge (27) while gripping the handle (32), then the cover (26) is brought into tight contact with the seat plate (28) by rotating the levers (31) about the bolts (29) in the direction of arrows, and thereby the leakage water through the plug (4) is prevented from flowing out through the manhole (25). According to the present invention, owing to the fact that a plug is disposed in a nozzle section of a coolant piping communicating with a water chamber in a steam generator for a pressurized water type nuclear reactor, the plug is supported by a support arm having an angle adjusting screw and fixedly secured to a mount seat at a manhole communicating with the same water chamber and a cover is provided on the mount seat at the same manhole, the nozzle section of the coolant piping communicating with the water chamber in the steam generator can be blocked by the plug and thereby the steam generator can be isolated from the other primary coolling systems. Accordingly, inspection and repair of thin tubes in the steam generator as well as routine inspection tasks relating to the nuclear reactor can be carried out in parallel and simultaneously, so that the period of routine inspection can be shortened, and therefore, the present invention can contribute to reduction of exposure to radiation and enhancement of an operation rate of an atomic power station. Moreover, since the plug is supported at a predetermined attitude from the support arm fixedly secured to the amount seat at the manhole by means of the angle adjusting screw, and since a hydraulic pressure applied to the plug is borne by the steam generator via the support arm, a special support means is unnecessary. Furthermore, owing to the fact that a cover is provided on the mount seat at the manhole, even if water should leak through the plug, the leakage water can be prevented from flowing out through the manhole. Since many changes and modifications can be made to the above-described construction without departing from the spirit of the present invention, it is intended that all matter contained in the above description and illustrated in the accompanying drawings shall be interpreted to be illustrative and not as a limitation to the scope of the invention.