Patent Number: 046844929
Section: summary

The invention relates to a repair fixture for water-cooled nuclear reactors. When making repairs on the walls of a reactor pressure vessel or when replacing primary shutdown controls of water-cooled nuclear reactors, these primary shutdown controls must be evacuated beforehand. However, this is only possible if the water level in the reactor pressure vessel is lowered to the extent that it is below the level of the primary shutdown controls to be repaired or below the level of the outlets of the respective conduits, such as the feedwater distributors. The same applies when repairs on the walls of the reactor pressure vessel become necessary. In the case of boiling water reactors and pressurized water reactors, this presupposes that all of the fuel elements must first have been removed from the core barrel. This is extremely costly. Moreover, during evacuation of the core barrel and during the lowering of the water level in the reactor pressure vessel, a perceptible radiation exposure of the operating and maintenance personnel is to be expected. Lastly, the lowering of the water level in boiling water reactors requires special shielding measures to be taken for the steam separator and steam dryer. It is accordingly an object of the invention to provide a repair fixture which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, and to provide means for performing repairs on the primary shutdown controls or even on the walls of a reactor pressure vessel, which can be carried out without having to lower the water level in the reactor pressure vessel. With the foregoing and other objects in view there is provided, in accordance with the invention, a repair fixture for water-cooled nuclear reactors including an openable reactor pressure vessel having a wall, and conduits passing through the pressure vessel wall for flooding the pressure vessel, comprising a sealing box disposed in the opened, flooded pressure vessel, means connected to the sealing box for pressing the sealing box liquid-proof or tightly, abutting against the pressure vessel wall enclosing at least some of the conduits, and means connected to the sealing box for evacuating the conduits enclosed by the sealing box. A sealing box which, according to the invention, can be liquid-tightly applied against the pressure vessel wall in the flooded reactor pressure vessel in vicinity of the feedwater distributors or conduit connections, permits the evacuation of covered wall areas including the feedwater distributors and conduit connections present at that location, with the reactor pressure vessel flooded. If primary shutdown controls are placed at the same level or higher, they are then evacuated at the same time. Otherwise, they can be evacuated through the connecting conduits. In accordance with another feature of the invention, the conduits are feedwater distributors having conduit connections leading to primary shutdown controls of the pressure vessel. In accordance with a further feature of the invention, there are included means disposed in the sealing box for mounting inspection, testing and treatment equipment. In accordance with an added feature of the invention, there is provided a support ring lowerable into the pressure vessel, the sealing box being mounted on the support ring. This greatly facilitates handling of the rather bulky sealing box. Such a support ring at the same time helps to transmit to the wall of the reactor pressure vessel, the compressive forces of the sealing box exerted against the inner surface of the wall of the reactor pressure vessel. In accordance with an additional feature of the invention, there is provided a core barrel disposed in the pressure vessel below the conduits, the support ring including props engaging the core barrel when the support ring is lowered. In accordance with again another feature of the invention, the support ring has an outer periphery including lateral props engaging the inner surface of the pressure vessel wall for absorbing radial compressive forces of the sealing box. In accordance with again a further feature of the invention, there are provided setting cylinders displacing the lateral props against the inner surface of the pressure vessel wall. The very efficient bracing of the support ring on the core barrel of the nuclear reactor defines a reference height of the support ring, from which the further displacement of the sealing box relative to the support ring can occur. At the same time, a crane will be available for other jobs, such as the repositioning of fuel elements, during the running repair measures. In accordance with again an added feature of the invention, there are provided means for displacing the sealing box in radial or circumferential direction of the support ring. In accordance with again an additional feature of the invention, the support ring has an axis of symmetry, and including a guide connected to the support ring in which the sealing box is displaceable vertically and parallel to the axis of symmetry. In this way, the sealing box can by-pass or pass behind guide rods extending along and spaced from the pressure vessel wall. In accordance with yet another feature of the invention, there are provided hydraulic cylinders controlling displacements radially, circumferentially and vertically of the sealing box relative to the support ring. In accordance with yet a further feature of the invention, there are provided guide cams between the sealing box and the support ring adapted to a given reactor type for forcibly displacing the sealing box in radial direction relative to the support ring. Such cams avoid damage due to improper manipulations which are not impossible, to say the least, with universal, freely selectable hydraulic adjustment. In accordance with yet an added feature of the invention, the pressure vessel has an axis of symmetry and contains fuel elements including outer fuel elements disposed at a given distance from the axis of symmetry, and the conduits are feedwater distributors protruding into the pressure vessel, and including a support ring on which the sealing box is mounted, the sealing box having a depth in radial direction of the pressure vessel being only that which is absolutely necessary to cover the protrusion of the feedwater distributors, and the support ring and the sealing box leaving an unobstructed inside diameter of the pressure vessel being more than twice the given distance, when the sealing box is pressed against the pressure vessel wall. In accordance with yet an additional feature of the invention, the sealing box has rims to be pressed against the pressure vessel wall, and sealing lips or gaskets disposed on the rims. In accordance with still another feature of the invention, each of the gaskets is substantially L-shaped and has a longer and a shorter leg, the longer leg being pressed against the pressure vessel wall and having a narrow sealing edge and a wide sealing lip, and a shallow fillet between the sealing lip and sealing edge. In accordance with still a further feature of the invention, the evacuating means include a pump. The evacuation of the conduits or feedwater distributors covered by the sealing box can be carried out with this construction. In accordance with still an added feature of the invention, there is provided a float switch disposed in the sealing box and connected to the pump for controlling the pump. In accordance with still an additional feature of the invention, the pump is disposed in the sealing box. This simple and expedient solution causes the pump to be switched on automatically if necessary in case of leaks or other intrusions of water. In accordance with another feature of the invention, the pressure vessel has a given water level, and including an air venting hose connected to the sealing box and leading above the water level. In accordance with a further feature of the invention, the conduits are in the form of four feedwater distributors connected to the pressure vessel, and including grommets and guides being screwed to the support ring and movable for repositioning along the periphery of the support ring toward the feedwater distributors. The traverses are also needed to manipulate other core inserts, such as water separators and are guided in many nuclear reactor types for automatic coupling or for exact deposition of these core inserts in the pressure vessel area and are not rotatable at will about the axis of symmetry thereof. For this reason, this construction is especially appropriate for covering the feedwater distributors, which are usually offset relative to each other by 90.degree. or 180.degree.. In this way, the sealing box can be repositioned by 90.degree., 180.degree. or 270.degree.. In accordance with an added feature of the invention, the support ring is divided into sections. This makes the support ring easier to transport to the site where it is used and to mount it between the inserts. In accordance with an additional feature of the invention, the sealing box is at least partly transparent. In accordance with again another feature of the invention, there are provided transparent windows disposed in the sealing box. In accordance with again a further feature of the invention, there are provided means disposed in the sealing box for mounting at least one light source and a television camera. In accordance with again an added feature of the invention, the mounting means includes means for moving and adjusting a television camera along the sealing box. In accordance with a concomitant feature of the invention, the mounting means are in the form of remotely controllable carriers for eddy current testing probes having ultrasonic testing heads and means for carrying out a color penetration method. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a repair fixture, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.