Patent Number: 059303182
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows part of a nuclear power plant comprising a reactor vessel 1 with a removed reactor vessel cover, not shown in the figure, arranged in a water-filled reactor pool 2. Further, a so-called fuel pool 3 is shown arranged adjacent to the reactor pool 2. The fuel pool 3 is substantially designed for temporary storage of new and completely or partially burnt-up fuel assemblies 4, respectively. The reactor vessel 1 comprises a core 5 with a plurality of fuel assemblies 4 and a core grid 6 arranged above the core 5. The reactor pool 2 is connected to the fuel pool 3 via a closable opening 7. The other internal parts 8 of the reactor can be temporarily arranged in the reactor pool 2. During shutdown of the nuclear reactor, the reactor vessel 1 is filled with water and the reactor vessel cover removed. Then, the reactor pool 2 above the reactor vessel 1 is filled with water and the gate 7 between the reactor pool 2 and the fuel pool 3 is opened. Internal reactor parts 8 arranged above the core 5 are lifted out and arranged in the reactor pool 2. The core grid 6 and the fuel assemblies 4 arranged below the grid are now available for handling equipment 9 arranged in the reactor hall. The handling equipment 9 comprises, for example, a telescopic arm 10, to the lower end of which a gripper 12 may be attached. Alternative embodiments of the gripper 12 are shown in more detail in FIGS. 3 and 4. The gripper 12 is lowered down into the reactor vessel 1 and lifts up a group 4a of fuel assemblies 4 therefrom. The fuel assemblies in the raised group 4a have the same mutual positions in the group as they have when they are arranged in the core 5 of the reactor vessel 1. The gripper then transports the group 4ato the fuel pool 3 by means of the handling equipment 9. FIG. 1 shows in dashed lines the gripper 12 during transport of a group 4a of fuel assemblies 4. The fuel assemblies 4 are lifted out through the openings in the core grid 6. FIG. 2 shows, in principle, the appearance of the core grid 6. The core grid 6 comprises a grid. The size of an opening in the grid corresponds to the size of a core module, that is, four adjacently located fuel assemblies 4 and one cruciform control rod 11 arranged therebetween. The control rods 11 may either be lifted out together with the fuel assemblies 4 or be left in the reactor core 5. The removed control rods are placed temporarily in the fuel pool 3 together wit h the fuel assemblies 4. In the fuel pool 3 the groups 4a are arranged in a conventional fuel stand (not shown). The upper limiting surface of the fuel stand in the fuel pool 3 is preferably made with a supporting structure with a shape corresponding to that of the core grid 6. in this way, the handling is facilitated with the aid of the gripper 12 used in that the gripper can be supported and guided with the a id of the supporting structure and the core grid 6, respectively, in the same way both in the core 5 and in the fuel pool 3. FIGS. 3a and 3b show a gripper 12 comprising eight gripping devices 13, one for each fuel assembly 4 to be lifted in a group 4a of eight fuel assemblies 4. Each gripping device 13 is connected to, for example, a telescopic arm 14 for lifting of the group 4a into and out of the core 5 or the fuel pool 3, respectively. The gripper 12 is intended for lifting fuel assemblies 4 only and is therefore provided with neutron-absorbing partitions 15. The partitions 15 are arranged such that two or three walls each surround a fuel assembly 4 lifted out of the core 5 or the fuel pool 3. The object of the partitions 15 is to prevent the occurrence of criticality when the fuel assemblies 4 are in this position. The corresponding fuel stand in the fuel pool 3 is preferably provided with corresponding neutron-absorbing walls 15 in corresponding positions with the same purpose. In one embodiment of the invention, as shown in FIGS. 3a and 3b, the gripper 12 may be provided with a sleeve 16 into which the fuel assemblies 4 are drawn. The sleeve 16 extends substantially along the whole length of the fuel assembly 4. At its end facing the core 5 and the fuel pool 3, respectively, the sleeve 16 is provided with guiding means 17. The object of the guiding means 17 is to position the gripper 12 with the aid of the core grid 6 and the supporting structure, respectively, in the fuel pool 3 such that the gripping devices are positioned correctly to be able to grip the fuel assemblies arranged below the core grid 6 and the supporting structure, respectively. The provision of the sleeve 16 is one way of preventing the fuel assemblies 4, drawn into the sleeve, from separating from each other or approaching each other in an unsuitable way during the transport. FIGS. 4a and 4b show a gripper 12 intended for handling of core modules wherein the control rod 11 is lifted together with four fuel assemblies 4. The gripper 12 according to FIGS. 4a, 4b differs from that shown in FIGS. 3a, 3b in that it has no partitions 15. When the control rod 11 is lifted out together with the fuel assemblies 4, no neutron-absorbing means is needed in the gripper 12. The gripper 12 in FIG. 4a is intended to simultaneously handle two core modules with one control rod 11 each. The gripper 12 can be designed according to the same principles as shown here for groups 4a with more or fewer fuel assemblies 4 and core modules, respectively. If two fuel assemblies 4 are to be lifted, preferably two fuel assemblies 4 positioned diagonally in relation to each other are lifted. The gripping devices 13 shown are shown in two-row design. It is, of course, possible to design the gripper 12 as a single-row or multi-row gripper depending on the design of the nuclear reactor in question. The positions for the groups 4a of fuel assemblies in the fuel pool may either be arbitrary or determined in such a way that fuel assemblies, and any control rods 11, removed from the reactor vessel 1 are given the same mutual order as they had when they were arranged in the reactor vessel 1. In one embodiment of the invention, the gripper comprises means 18 to increase and decrease, respectively, the mutual distance between the fuel assemblies once they have been lifted by the gripper. This is advantageous when the fuel stand in the fuel pool 3 does not have the same pitch measure as the core grid 6.