Patent Number: 046844929
Section: description

Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a cross-sectional view of the upper part of a biological shield 1 of a containment 2, and an opened reactor pressure vessel 3 with a repair fixture 4 according to the invention in place. In the representation of FIG. 1, a support ring 5 and a sealing box 6 of the repair fixture 4 have been lowered into the flooded reactor pressure vessel 3 on a traverse 7 which is suspended from a crane harness 8 of the reactor building. The traverse 7 is lowered into the reactor pressure vessel 3 far enough for support props 9 to 11 of the support ring 5 shown in FIGS. 1 and 2 to sit on an upper rim 12 of a core barrel 13. In this position, the sealing box 6 mounted on the traverse 7 covers a feedwater distributor 14 toward the right side of FIG. 1. The sealing box 6 has a rim 15 provided with a peripheral gasket 16 which abuts the inner surface of the wall of the reactor pressure vessel 3. Three remaining feedwater distributors 17 to 19 shown in FIG. 2 are not covered. Lateral props 20 to 23, which are adjustable by means of setting cylinders 24 to 27, brace the support ring 5 against the inner surface of the wall of the reactor pressure vessel 3. A pump 28 is attached to the support ring 5, below the sealing box 6. The pump 28 has a suction nipple 29 which is connected by a hose 30 with the interior of the sealing box. A float switch 31 is disposed in the sealing box and is inserted into the circulation caused by the pump 28. An outflow nipple 32 of the pump 28 is secured through a non-illustrated check valve and discharges directly below the pump. FIGS. 1 and 3 show that the sealing box 6 is connected with the support ring ring 5 through four booms 33 to 36. These booms in turn are displaceable parallel to the axis of symmetry 39 of the support ring, i.e. vertically in two vertical guides 37, 38 attached to the support ring 5 at the top and bottom thereof. FIGS. 1 and 3 also show that the booms 33 to 36 are not only adjustable in height along the guides 37, 38 on both sides of the sealing box 6, but can also be pivoted about these guides. The height or vertical adjustment occurs through the use of the hydraulic cylinders 40, 41 attached on the support ring, parallel to the guides. In order to pivot the booms 33 to 36, two additional hydraulic cylinders 42, 43 are disposed on the support ring. The hydraulic fluid for the cylinders may be pure water to prevent contamination of the flooded pressure vessel. As seen in FIG. 3, each of the cylinders 42, 43 have piston rods which engage the pivotable end of one of the booms 33, 35. The upper and lower ends of the sealing box 6 each carry two guide tracks 44, 45, each of which are displaceably guided in the ends of the booms 33 to 36, although only two tracks are shown. The sealing box 6 is displaced radially relative to the support ring 5, by simultaneously swinging the booms in opposite directions. However, since the sealing box 6 is displaceable along the guide tracks 44, 45 relative to the booms 33, 35 toward both sides, a slide block 46 with a bent guide track 47 can be screwed to the support ring 5 above the sealing box. A pin 48 fastened to the sealing box engages in the bent guide track 47. The pin 48 which is displaceable along the bent guide track 47 of the slide block 46, not only permits the sealing box 6 to be advanced radially during the pivoting of the booms 33 to 36, but simultaneously permits it to be displaced laterally and thus guided laterally past the inserts. FIG. 4 shows how the gasket or sealing ring 16 is attached to the rim 15 of the sealing box 6 by a clamping ring 49. FIG. 4 shows a substantially L-shaped contour of the sealing ring 16, which has a fillet 50 in vicinity of the abutment surface. The fillet 50 divides the sealing surface of the sealing ring into a narrow sealing edge 16' and a greatly extended sealing lip 16". The narrow sealing edge will be more easily deformed or pressed into unevennesses by the pressing force of the sealing box, while the sealing lip is preferably applied through the use of the pressure difference. In addition, the sealing lip is pressed against the wall of the reactor pressure vessel by a spring blade 63. Primary shutdown controls 51', 52' of a water-cooled nuclear reactor, which are disposed outside the biological shield 1 and which are connected to the reactor pressure vessel 3, may have to be repaired or replaced. Heretofore, it was necessary to remove the fuel elements from the core barrel to evacuate these primary shutdown controls, so that the reactor pressure vessel 3 could be evacuated to the extent that the feedwater distributors 14, 17, 18, 19 or the conduit connections would lie above the water surface and could be evacuated. According to the invention, after removal of the pressure vessel cover and of the other inserts, it is sufficient to lower the support ring 5 with the sealing boxes 6 attached thereto with the aid of the crane harness 8 of the reactor building, into the flooded reactor pressure vessel 3. This is done until the support props 9, 10, 11 of the support ring 5 rest on the upper rim 12 of the core barrel 13. In this defined position, the lateral props 20, 21, 23 distributed over the periphery of the support ring can be brought into abutment with the inner surface of the wall of the reactor pressure vessel 3, through the use of the setting cylinders 24 to 27, which are actuated by pressurized water. The support ring 5 is then fixed in height as well as relative to the axis of symmetry 39 of the reactor pressure vessel 3. The booms 33 to 36 carrying the sealing box can therefore be displaced along the vertical guides 37, 38 with the vertical hydraulic cylinders 40, 41, until the sealing box is vertically centered on the feedwater distributors 14, 17, 18, 19 to be covered. By then swinging the booms 33 to 36 apart by means of the hydraulic cylinders 42, 43 disposed below the sealing box, the sealing box 6 can be pushed radially outwardly over one of the feedwater distributors 14, 17, 18, 19 and against the inner surface of the wall of the reactor pressure vessel 3, until its peripheral rim having the gasket 16 attached thereto is applied against the inner surface of the wall of the reactor pressure vessel. As soon as this is done, the pump 28 which is suspended from the support ring below the sealing box 6 can be turned on and the sealing box can be pumped empty. The water then also runs out of the feedwater distributor 14 and the other covered conduits including conduit connections 14' and the primary shutdown control 51' connected thereto and the water runs into the sealing box 6. The water then runs from the sealing box through the outflow nipple 32 of the pump 28 into the open, flooded reactor pressure vessel 3, and air flows into the sealing box from a venting hose 53. After complete evacuation of the sealing box 6 as well as the conduits discharging therein, the pump 28 automatically turns off through the float switch 31 disposed in the sealing box 6. If an intrusion of water or a sufficient amount of leakage water has accumulated in the sealing box, the float switch 31 switches the pump on again, if necessary. In some boiling water reactors, guide rods for other inserts extend upward adjacent the feedwater distributors. The guide rods can hinder the radial abutment of the sealing box. In such cases, the sealing box 6 can be lifted over these obstacles by means of the vertical hydraulic cylinders 40, 41 before it abuts against the pressure vessel wall. Alternatively, the sealing box 6 can be moved past the obstacle laterally, by using the slide block 46 adapted to the respective reactor type, if this is easier to perform. The sealing box may also be supported by rotating the entire support ring 5 by means of the crane harness 8, unless the traverse 7 is non-rotationally guided in the reactor pressure vessel. In this way, such obstacles can be by-passed with the sealing box or the sealing box can go behind the obstacles if the distance from the wall is sufficient. The primary shutdown controls 51', 52' evacuated in the above described manner can thus be removed without first having to remove the fuel elements 13' from the core barrel 13, and the water level in the reactor pressure vessel 3 lowered. After completed servicing or replacement of the primary shutdown controls and after flooding by actuation of the hydraulic cylinders 42, 43, pivoting the booms 33 to 36, the sealing box can be pulled off the wall of the reactor pressure vessel again and can be moved out of the reactor pressure vessel by the crane harness 8, together with the support ring 5. If the traverse 7 is not secured against rotation in the reactor pressure vessel 3, the other feedwater distributors 17 and 19, which are usually offset relative to each other by 90.degree., and the conduit connections, can be serviced or replaced in the described manner one after the other. This is done by respective rotation of the traverse 7, with the support ring 5 attached thereto, about a corresponding angle and by renewed lowering. However, if the traverse is secured against rotation, the sealing box 6 as well as the grommets, guides and slide blocks on the support ring 5 must instead be repositioned, so that the traverse 7 need not be rotated about the axis of symmetry 39 of the reactor pressure vessel 3 and instead the support ring 5 may be rotated about the axis of symmetry and can be suspended from the traverse 7 again. For this reason, these structural mambers are secured to the support ring to be unscrewed and rescrewed. Transportation to and from the site as well as storage of the support ring are also considerably simplified in the case of a divided, bolted support ring. Due to the fact that the inside diameter of the support ring is unobstructed and its clearance is adapted to the diameter of the rim of the core barrel and adjusted thereto during the repair of the primary shutdown controls, the crane of the reactor building remains free for the duration of the repair or replacement. Thus, for example, fuel elements can be repositioned in the meantime. The down time of the nuclear reactor is therefore greatly shortened in addition. Naturally, the sealing box can not only be used to evacuate certain conduits discharging into the reactor pressure vessel when the vessel is flooded, but also for the purpose of checking and repairing any desired wall areas of the reactor pressure vessel by various methods which would otherwise not be usable. Thus, not only can light sources and television cameras be lodged in the sealing box in order to view the covered wall areas, but remote controllable eddy current probes and devices for carrying out the color penetration method which could otherwise not be used in flooded wall sections, may also be installed in the sealing box. Lastly, the sealing box, which is already pressed firmly against the wall of the reactor pressure vessel as a result of hydrostatic pressure, offers a useful platform for operating remote controllable grinding, milling and welding machines in the sealing box. Thus, all kinds of repairs can be carried out under television control and without appreciable radiation exposure. In this connection, it is especially helpful if windows 54 to 60, 61 and 62 are inserted in the wall of the sealing box 6, as indicated in FIGS. 1 and 3, for external observation by additional television cameras and/or light sources. In the repair fixture 4 shown as an example in FIGS. 1 to 3, the slide block 46 could be replaced by a hydraulic main cylinder. On the other hand, the two hydraulic cylinders 40, 41 responsible for the vertical displacement of the sealing box could be replaced by slide blocks 40a, 41a adapted to the local condition of the respective reactor type. The slide blocks raise the booms during pivoting as far as is appropriate for that reactor type. The positive guiding of the sealing box by slide blocks or guide cams prevents incorrect manipulations.