Patent Number: 039430375
Section: summary

BACKGROUND OF THE INVENTION In heterogeneous nuclear reactors, the used fuel elements have to be replaced or rearranged in the reactor core after predetermined time intervals. In water reactors, such a fuel element exchange may be effected in two ways: In case of a so-called "dry" exchange, the fuel element is drawn under water into a closable steel container and the latter is, together with the enclosed cooling water and the fuel element, transported into a fuel element storage pool. In case of a so-called "wet" fuel element exchange, the reactor pool and the adjacent fuel element storage pool are interconnected by means of a channel in which there is disposed a watertight gate. As a preparatory step to the wet fuel element exchange, the water level in the reactor pool is raised to the water level in the fuel element storage pool and the gate is opened. Subsequently, the fuel elements may be grasped with specially designed tools mounted on a travelling fuel element exchange gantry and moved through the connecting channel between the reactor and the assigned storage space in the fuel element storage pool. In case the fuel elements are disposed in sheaths (boxes), a conventional box-stripping machine has to be provided in addition. The invention relates to a system for performing a wet fuel element exchange process. Heretofore, for effecting this type of exchange, the rails on which the gantry travels have been disposed at the same height as the edge of the fuel element storage pool and the level of the operating platform. Further, the box-stripping machines and tool storing devices have been disposed in the rear part of the fuel element storage pool which requires that these apparatuses project beyond the pool edge. It is a disadvantage of the above-outlined known systems for effecting a wet fuel element exchange that they involve long travelling paths and thus require long periods of reactor shutdowns. SUMMARY OF THE INVENTION It is an object of the invention to provide an improved system for effecting a wet fuel element exchange, by means of which the duration of the fuel element exchange process can be shortened. This and other objects to become apparent as the specification progresses, are achieved by the invention according to which, briefly stated, there are provided a first fuel element exchange gantry supported on a column disposed in the center of the reactor building and on a rail which is held by the building wall and which is situated above the level of the operating platform, and a second fuel element exchange gantry supported under the first gantry in such a manner that the second gantry may freely pass under the first gantry. There is further provided a fuel element box-stripping machine at the storage pool immediately across from the channel in the operational range of both the first and the second gantries. The advantage of the invention resides in the shortening of travelling paths and thus time saving in the performance of the fuel element exchange operation is accomplished. The shortening of the paths result principally from the arrangement of the box-stripping machine or machines at the fuel element storage pool directly across from the connecting channel. The disposition of the box-stripping machine and the tool storing devices, if any, directly across from the connecting channel and the thus accomplished shortening of the travelling paths during the fuel element exchange are made possible by arranging the main fuel element exchange gantry above the level of the operating platform. Further, in the system according to the invention, there is effected a division of the fuel element handling between two exchange gantries, resulting in a further time saving.