Patent Number: 048636746
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a low capacity gas cooled nuclear reactor installation and particularly an installation with a stationarily spherical fuel element pile located in a reactor vessel. The reactor vessel is housed in a cavity. The reactor vessel exhibits an access opening. The building overlapping at least the cavity cover comprises means for manipulating the operating elements. 2. Description of the Related Technology DE-OS 35 18 968, the disclosure of which is expressly incorporated herein, shows a reactor installation with a stationary lifting device. Following completion of a power operation period of several years, the cavity is opened and the core vessel removed together with the operating elements contained therein. A shielding bell large enough to receive the entire core vessel is provided in the building and located over the cavity. The shielding bell must be large and heavy if it is part of a transport container. If the operating elements are reloaded from the shielding bell into a transport container additional effort, questionable from a safety standpoint, is required. SUMMARY OF THE INVENTION An object of the invention is to simplify and enable improved radiation safety during manipulation of operating elements in a reactor installation. This object is attained according to the invention by setting a transport container on a cavity cover where the transport container bottom overlaps the cover access opening. A vertically displaceable pebble conveyor line extends from the pebble pile surface through the bottom of the transport container and into the transport container. A blower is located between the transport container and the reactor vessel. The suction line of the blower is connected to the inside of the transport container and its pressure line leads into the reactor core. The constantly circulating gas flow entrains the spherical operating elements into the transport container. The vertically displeacable pebble conveyor line is arranged to insure that its projecting end always remains in the immediate vicinity of the pebble pile surface. The frontal side of the pebble conveyor line facing the pile has a contour differing from the horizontal and may be rotated around its axle to facilitate seizing and entrainment of the spherical operating elements by gas flow. Advantageously, a favorable pebble transport is achieved by utilizing a corrugated tube with internal longitudinal ribs as the pebble conveyor line. A guide tube resembling a walking stick extends from the bottom of the transport container approximately vertically into the inner space, so that the guide tube extends to the vicinity of the cover of the transport container in order to fully and easily load the transport container directly under its cover. The pebble is displaceably guided in the guide tube. The guide tube serves to guide the pebble conveyor line and the pebbles, in order to load the transport container from the top. The bottom of the transport container is traversed by a bore extending concentrically relative to the guide tube resembling a walking stick and a further bore receiving the blower suction line. The passages may be closed by ball valves and with a shielding stopper located on a closure cover following completion of the charging process. According to a preferred embodiment the transport container exhibits an intermediate bottom in the form of a filter to support the operating elements and the suction line terminates under the intermediate bottom in order to prevent the suction line from suctioning dust particles from the transport container. A displaceable frame with a hydraulic lifting device is preferably arranged in the housing. The frame moves the transport container between its place of application above the access opening and a transport vehicle located outside the housing. This eliminates the need for a stationary lifting tool and a correspondingly more extensive housing configuration. A rotating and advance unit is associated with the conveyor line for the vertical and rotating motion of the pebble conveyor line. The unit is preferably fastened to a closure slide housing assigned to the reactor vessel. Advantageous configurations of the rotating and advance unit are set forth below. The frontal side of the pebble conveyor line, facing the pile, may advantageously be angled and non-horizontal and may be rotated around its axle. The pebble conveyor line may be a corrugated tube with longitudinal inner ribs. A guide tube resembling a walking stick in shape extends from the bottom of the transport container approximately vertically into the inner space of the container. The guide tube extends into the vicinity of the cover of the transport container and the pebble conveyor line is arranged in the guide tube in a vertically displaceable manner. The transport container bottom is traversed by a bore extending concentrically with the guide tube and may exhibit an inline ball valve. A bore may also be provided in the transport container bottom for passage of the suction line, and the bore may be closed off by a ball valve. A closure cover may be mounted under the container bottom. The cover carries shielding stoppers which extend into the bottom bores. The bore ball valves may be accessible by inserts releasably located in the bottom. The transport container may advantageously comprise an intermediate bottom in the form of a filter for supporting the operating elements and the suction line terminates under the intermediate bottom. A movable frame with a hydraulic lifting device may advantageously be provided in the building. The movable frame carries the transport container between its operational position above the access opening and a transport vehicle located outside the building. The rotating and advance unit is advantageously associated between the transport container and the reactor vessel with the pebble conveyor line. The rotating and advance unit may be mounted on the housing of a closure slide associated with the reactor vessel. A covering sleeve may extend between the rotating and advance unit and the transport container bottom. The covering sleeve may concentrically surround the pebble conveyor line while leaving a certain clearance. The rotating and advance unit concentrically surrounds the pebble conveyor and is equipped with a pneumatically controlled stepping piston movable in the axial direction with or without the pebble conveyor line. The rotating and advance unit also includes a holder device and a drive rotatable with the pebble conveyor line. The stepping piston and the holding device may be equipped with a plurality of clamping jaws on their surface areas facing the pebble conveyor line. The clamping jaws may be applied to the pebble conveyor line by pneumatically actuated setting elements. The holding device and the stepping piston are alternatingly frictionally connected to the pebble conveyor line. A process for the replacement of the operating elements in a nuclear reactor installation according to the invention is characterized in that the primary loop is operated without pressure and the cooling gas is stored intermediately. The operating elements are conveyed by a circulating gas flow between the transport container and the reactor vessel into the transport container. The transport container is separated after it is filled with burned operating elements from the circulating gas flow. A container with new fuel elements is connected to the circulating gas flow. The operating elements arrive through the pebble conveyor line in the reactor vessel by their own gravity. A braking action is applied to the falling pebbles by adjustment of the blower output. The pebble conveyor line end facing the pebble pile is constantly maintained at the height of the surface of the pebble pile. The cooling gas is recirculated from its intermediate storage, into the primary loop and gas losses are equalized by a reservoir. The advantages of such a process are to be found primarily in that the replacement of the operating elements may be carried out with the nuclear reactor not under pressure, no gas purification means are required and mobile devices are used which may be applied to multiple installations. A nuclear reactor installation according to the invention and a process for the replacement of operating elements in such a nuclear reactor are described below by way of example and with reference to FIGS. 1 to 6.