Patent Number: 053512774
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of constructing the top slab of a steel-reinforced concrete nuclear reactor container in a nuclear power generating plant and also to a nuclear reactor container constructed by such a method. 2. Description of the Related Art A known construction method will be described with reference to FIG. 5 which shows the construction of a nuclear reactor container made of steel-reinforced concrete, FIG. 6 which is an illustration of a top slab portion of the nuclear reactor container, illustrative of the conventional construction method and FIG. 7 which is a flow chart of the known construction method. The nuclear reactor container made of steel-reinforced concrete has a bottom-equipped cylindrical portion 2, a top slab 4 and a top head 5. The interior of the container is divided into two spaces by a diaphragm floor 3. The nuclear reactor container contains a pressure vessel 6 of a nuclear reactor and forms a portion of a nuclear reactor house 1. The known construction method will be described with specific reference to FIGS. 6 and 7. After mounting a liner 11 for the cylindrical portion, temporary posts 14 and temporary trusses 15 are installed and a top slab liner 10 is placed on the top of the temporary trusses 15. A flanged sleeve 7 of the nuclear reactor container is set up and welding is conducted at the welding lines 12 and 13. Then, doughnut-shaped top slab reinforcers 8 are assembled on the top slab liner 10. Subsequently, the reinforcers 9 for the cylindrical portion are set up and connected to the top slab reinforcers 8. Then, a concrete is poured and, after drying and solidification of the concrete, the temporary posts 14 and the temporary trusses 15 are removed. Arts pertaining to this known construction method are: a method of constructing a cylindrical liner (Japanese Patent Laid-Open No. 62-170885), a method in which beams are extended through a steel-reinforced concrete top slab forming the upper structure of a nuclear reactor core, the beams being connected to a lining (Japanese Patent Laid-Open No. 62-165185), a non-unitizing top slab installation method (Japanese Patent Laid-Open No. 62-169082), an art relating to liner structure of cylindrical a portion of a reactor container (Japanese Patent Laid-Open No. 62- 298794), and a method of laying steel reinforcers (Japanese Patent Laid-Open No. 64-74498). The following arts are also proposed: a hollow pre-cast slab incorporating steel reinforcement beams and a method of producing the same (Japanese Patent Laid-Open No. 49-111420), a method of constructing a floor using a deck plate in place of a frame (Japanese Patent Laid-Open No. 52-26714), a method of constructing an intermediate slab of a base structure of nuclear 2 reactor for supporting a nuclear reactor pressure vessel (Japanese Patent Laid-Open No. 56-125691), a method in which an H-shaped steel is attached to each side of a lining for a concrete container (Japanese Patent Laid-Open No. 57-19696), a method in which works such as attaching of trays with ceilings, ducts, pipes and supporting structures are to deck beams and set-up of pipes to upper side of beams are conducted in a factory thus unitizing ceiling deck plate (Japanese Patent Laid-Open No. 57-57289), a method of lining the side wall of a reactor container made of steel-reinforced concrete, wherein the liner is integrated with steel reinforcers (Japanese Patent Laid-Open No. 59-142496), a method in which pipes to be buried in the floor of a reactor house are assembled in steel reinforcer units (Japanese Patent Laid-Open No. 62-273347), and a method in which steel reinforcers of a cylindrical portion of a shield wall is assembled from a plurality of units (Japanese Patent Laid-Open No. 64-79693). In these known arts, however, no consideration has been given to the efficiency in constructing a nuclear reactor container having a sleeve with a flange of an outside diameter which is greater than the inside diameter of a doughnut-shaped steel-reinforced structure. This problem has caused an impediment in constructing a nuclear reactor container. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method of constructing the top slab of a nuclear reactor container which can shorten the period of work even when the container has a sleeve with a flange of an outside diameter greater than the inside diameter of a doughnut-shaped steel reinforcement structure, as well as a nuclear reactor container constructed by such a method. To this end, according to one aspect of the present invention, there is provided a method of constructing the top slab of a nuclear reactor container, comprising the steps of: placing a container sleeve without a flange at a position where the top slab is to be constructed; lifting a prefabricated doughnut-shaped steel reinforcement structure and placing this structure at a position where it forms the top slab; and welding a flange for mounting a top head of the container to the sleeve. Preferably, the prefabricated doughnut-shaped steel reinforcement structure has an auxiliary plate integrated therewith and located so as to face the flange of the container after the welding of the flange. It is also preferred that the welding of the flange and the sleeve is conducted simultaneously with placement of concrete in the space next to the space between the auxiliary plate and the container sleeve followed by placement of concrete in the space defined by the auxiliary plate, the flange and the sleeve. The invention also provides a method of constructing the top slab of a nuclear reactor container, comprising the steps of: prefabricating a structure integrating a top slab liner, a container sleeve fixed to the inner periphery of the top slab liner substantially orthogonal to the top slab liner, and a doughnut-shaped steel reinforcement structure on the top slab liner, and lifting and mounting the prefabricated structure to a position where the top slab is to be constructed; and welding a flange for mounting a top head of the container to the container sleeve. Preferably, the prefabricated doughnut-shaped steel reinforcement structure has an auxiliary plate integrated therewith and located near the innermost circumference of the doughnut-shaped steel reinforcement structure. It is also preferred that the welding of the flange to the container sleeve is conducted simultaneously with placement of concrete in the space which is on the opposite side of the auxiliary plate to the flange and the container sleeve, followed by placement of concrete in the space defined by the auxiliary plate, the flange and the container sleeve. According to another aspect of the present invention, there is provided a nuclear reactor container, comprising: a bottom-equipped cylindrical portion for containing a nuclear reactor therein; a top slab provided on the top of the cylindrical portion and composed of a doughnut-shaped steel reinforcement structure and concrete placed integrally with the steel reinforcement structure, the top slab having a central bore; a sleeve outlining in the central bore of the flange and a flange fixed by welding to the sleeve and having an outside diameter greater than the inside diameter of the doughnut-shaped steel reinforcement structure; and a top head attached to the flange. Preferably, the steel reinforcement structure has an auxiliary plate located near the innermost circumference of the doughnut-shaped steel reinforcement structure. According to the invention, the flange portion is formed separately from the sleeve and is then fixed to the sleeve by welding. In the case where the outside diameter of the flange is greater than the inside diameter of the doughnut-shaped steel-reinforced structure, the flange can be welded to the sleeve after installation of the steel reinforcement structure, so that the term of construction work can be greatly shortened. According to the invention, it is also possible to integrate the steel reinforcement structure of the top slab, top slab liner and the sleeve and to install this integral structure as a unit. This eliminates the necessity for temporary trusses and, hence, further contributes to improvement in the efficiency of the construction work. According to the present invention, the sleeve and the flange are split so that the installation of the above-mentioned integral structure is facilitated. A cylindrical auxiliary plate, while strengthening the steel-reinforced prefabricated structure so as to prevent any deformation of the prefabricated structure during installation of the same, also prevents hiding the welding line between the flange and the container sleeve by concrete, thus enabling welding and inspecting of the weld to be executed simultaneously with the placement of concrete in a space on the outer diameter side of the cylindrical auxiliary plate. After flange and the container sleeve is welded, the concrete is placed in the space between the cylindrical auxiliary plate and the container sleeve.