Patent Number: 048184721
Section: summary

The invention relates to a method and an apparatus for the wet dismantling or disintegration of radioactively contaminated or activated components of nuclear reactor plants, wherein the component is provided with a sheathing having a thickness permitting it to perform the supporting function of a receptacle container for at least a part of the component after dismantling or disintegrating the component into individual pieces, the component is flooded with water for shielding radiation, the component is at least partly dismantled into individual pieces by a material-removing tooling or machining method, and the individual pieces are removed. Dismantling and crushing of a reactor pressure vessel in nuclear power plants is made more difficult by the contamination and activation resulting from neutron bombardment. The resultant radiation load on the operating staff can be kept at a low level by providing short staff exposure times, good shielding against radiation and remote control operation of the equipment. When radioactive components are disassembled, all of these three criteria are accordingly combined. The disassembly and crushing of a reactor pressure vessel can either be performed dry, i.e., in air, or under water. During remote-controlled dry dismantling or disintegration, which is performed under suitably shielding conditions using thick shielding plates, poor accessibility causes difficulties in extracting the radioactive elements. Moreover, if trouble is encountered during dismantling, the poor accessibility presents even further difficulties. During wet dismantling or disintegration, the good shielding effect of the water is exploited. It is known from the journal Electrical World, Feb. 15, 1978, page 47/48, to dismantle a demonstration reactor by filling both the safety vessel that surrounds the reactor vessel having the cooling system and the pool for spent and new fuel assemblies with water for shielding against radioactive radiation and by crushing the reactor vessel into small fragments. The fragments are first moved to a storage pool with a crane and are then delivered to a final storage location. With this conventional method, great quantities of radioactive waste are produced and the final storage thereof entails high costs. FIG. 1 of U.S. Pat. No. 3,158,546 discloses a nuclear power plant having a reactor pressure vessel disposed in a concrete pit, which is lined on the inside with a separate vessel to approximately 2/3 the height of the reactor pressure vessel. This vessel extends only up to a predetermined height of the concrete pit, not up to the height of the reactor pressure vessel, so that the reactor pressure vessel cannot be placed completely under water from the outside. If a reactor pit of this kind or such a pit that is not lined with an additional vessel were to be flooded for dismantling the reactor pressure vessel, leaks in the concrete and in the liner, if a liner is used, could lead to problems. After many years in operation, fissures in the concrete or in the biological shield which are in fact possible, result in a spreading of the contamination and hence in a greatly increased amount of radioactive waste. It is accordingly an object of the invention to provide a method and apparatus for the wet dismantling or disintegration of radioactively contaminated or activated components of nuclear reactor plants, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type, and which enables dismantling to be performed with simple means, while avoiding the spread of contamination into the biological shield even when the biological shield surrounding the component is not lined in advance with a water-tight vessel. With the foregoing and other objects in view there is provided, in accordance with the invention, a method for the wet dismantling of radioactively contaminated or activated components of nuclear reactor plants, which comprises enclosing the component with a jacket at the end of the service life of the component, providing a sheathing between the component and the jacket having a thickness sufficient to support at least part of the component after dismantling the component into individual pieces, flooding the component with water for radiation shielding, at least partly dismantling the component into individual pieces through a material removing method, and removing the individual pieces. With the objects of the invention in view there is also provided an apparatus for the wet dismantling of radioactively contaminated or activated components of nuclear reactor plants, comprising a jacket enclosing the component, and a sheathing in the form of shielding material disposed between the component and the jacket, the sheathing having a thickness sufficient to support at least a part of the component after dismantling the component into individual pieces. With the objects of the invention in view there is additionally provided a method for the wet dismantling of a radioactively contaminated or activated reactor pressure vessel disposed inside a reactor pit and spaced from a concrete biological shield defining a gap between the pressure vessel and the shield, which comprises severing coolant lines and closing connector stumps of the reactor pressure vessel, subsequently filling the gap between the pressure vessel and the shield by casting or injection molding forming a sheathing having a thickness sufficient to support at least part of the component after dismantling the component into individual pieces, flooding the component with water for radiation shielding, at least partly dismantling the component into individual pieces through a material removing method, and removing the individual pieces. With the objects of the invention in view there is furthermore provided an apparatus for the wet dismantling of a radioactively contaminated or activated reactor pressure vessel disposed inside a reactor pit and spaced from a concrete biological shield defining a gap between the pressure vessel and the shield, comprising a sheathing filling the gap between the reactor pressure vessel and the shield by casting or injection molding after severing coolant lines and closing connector stumps of the reactor pressure vessel, the sheathing having a thickness sufficient to support at least part of the component after dismantling the component into individual pieces. With the objects of the invention in view there is also provided a method for the wet dismantling of a radioactively contaminated or activated pressure vessel of a nuclear reactor plant, which comprises placing a bottom plate with a given diameter below the reactor pressure vessel, enclosing the pressure vessel with an enclosure tube having a lower end with the given diameter, tightly joining the lower end of the tube to the bottom plate, flooding the pressure vessel with water for radiation shielding, at least partly dismantling the pressure vessel into individual pieces through a material removing method, and removing the individual pieces. With the objects of the invention in view there is additionally provided an apparatus for the wet dismantling of a radioactively contaminated or activated pressure vessel of a nuclear reactor plant, comprising a bottom plate with a given diameter disposed below the reactor pressure vessel, and an enclosure tube enclosing the pressure vessel, the tube having a lower end with the given diameter tightly joined to the bottom plate. With the objects of the invention in view there is furthermore provided an apparatus for the wet dismantling of a radioactively contaminated or activated pressure vessel of a nuclear reactor plant having a bottom with a given diameter, comprising an enclosure tube enclosing the pressure vessel, the tube having a lower end with the given diameter tightly joined to the bottom of the pressure vessel. The advantages attainable with the invention are above all that it can be adapted to the most varied conditions in a reactor building and is therefore highly flexible. Typically, the thermal insulation formed of individual modules which is secured to the inner periphery of the biological shield and correspondingly the thermal insulation elements disposed on the bottom, are removed prior to the disposition of the sheathing. The dismantling or disintegration can be performed successively and the individual pieces can be removed from the sheathing and deposited in a spent fuel cooling pool or in a barrel for final storage. Prior to the disposition of the sheathing by integral casting or extrusion coating, in order to reinforce the sheathing and make it stronger, it may be suitable to provide the component with a framework or a skeleton of a reinforcement, which is suitably formed of annular members and jacket members, so that the result is a reinforcement network that covers the entire outer surface of the component. This network is then joined to or cast integral with the casting compound of the sheathing. When an enclosure tube is used, the outer diameter thereof is preferably dimensioned in such a way as to leave the smallest possible air gap between the tube and the reactor pit. 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 method and apparatus for wet dismantling or disintegration of radioactively contaminated or activated components of nuclear reactor plants, 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. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.