Patent Number: 054835623
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1a-c show a volume delimitation tank 1 according to the invention immersed into a fuel pool or a reactor pool 2. The shown tank 1 is intended to be used for scrapping control rods 3. In FIGS. 1a-c, the numeral 4 designates the protective concrete around the fuel or reactor pools 2 in the reactor building. The tank 1 is arranged suspended in the pool 2 and is attached to the edge 5 of the pool in a beam structure 6. The tank 1 substantially comprises vertical walls 1a-d shaped to form a channel and a box-shaped bottom part 9 for capturing debris. The tank 1 may, for example, have a height of 10 meters and the bottom part 9 may, for example, have an area of 5.times.3 meters. Inside the tank 1 there is a frame structure 10 for suspension of tools, such as a first spark machining device 11 and a gas hood 12. The frame structure 10 is also provided with two platforms 13 for the arrangement of tools such as a second spark machining device 14, a plugging device 15 and with machining positions for the objects which are to be machined. At the bottom of the tank 1, a cleaning device 16 is arranged, with an inlet conduit 17 and an outlet conduit 18 for continuously cleaning the contained volume. When scrapping control rods 3, the volume delimitation tank 1 is used, for example, in a work cycle as follows: 1. Divisible support rods 19 intended to support at least the vertical walls 1a-d of the tank 1 are mounted. The walls 1a-d formed of a channel are arranged at the bottom part 9, whereafter the support rods 19 are arranged at the walls 1a-d. The size of the tank 1 is chosen according to the size of the object to be machined or according to other needs, such as the size of the machining equipment. As clearly shown in FIGS. 2a and 3a, the tank has an open top through which, as seen in FIGS. 1a and 1b, control rods 3 can be inserted and can be clearly viewed from above, when carrying out the invention. 2. The volume delimitation tank 1 with the support rods 19 and the bottom part 9 are lowered into the pool 2, whereby the tank 1 is filled with water from the pool. The vertical walls 1a-d of the tank 1 unfold or form folds. The tank 1 is arranged at the beam structure 6 with substantially horizontal beams 7 projecting over the pool 2. 3. The divisible frame structure 10 is mounted and provided with two platforms 13 for tools. The frame structure 10 is lowered into the tank 1 and arranged at the beams 6 on the pool edge 5. The tank 1 may be attached to the frame structure 10 instead of being attached to the beams 6, or both to the beams 6 and to the frame structure 10. 4. The remotely operated tools which are used for the machining are lowered down into the tank 1 and arranged at a suitable location at the frame structure 10. A scrap stand 20 for scrapped control rods 3 is arranged at the frame structure 10. 5. The control rod/rods to be scrapped is/are moved into the tank and arranged in a machining position or in a waiting position 21. 6. The scrapping operation is started whereby control rods 3 are transferred one at a time, by means of a remotely operated gripping tool (not shown), to a first machining position, a cutting position 22 where the shafts 23 of the control rods are cut off by means of the second spark machining device 14. Gases which may then leak out from the control rod 3, such as tritium and/or deuterium, are evacuated continuously via the openable gas hood 12. The shaft 23 is brought to the scrap stand 20, whereafter the hole left in the control rod 3 by the shaft 23, by means of the plugging device 15 in a second machining position 24, is plugged up to prevent further gas leakage. After the plugging, the control rod 3 is brought to a third machining position 25 where two opposed control rod blades of the cruciform control rod 3 are dismantled by means of the first spark machining device 11, whereafter they are arranged together with the non-dismantled control rod blades in the scrap stand 20. The work in the separate positions 22, 24, 25 can take place in parallel. The water is cleaned continuously during the entire work cycle by means of the cleaning device 16, which admits water via the inlet conduit 17 from the lower part of the tank, as well as at the spark gaps, that is, at the first and the second spark machining device 11, 14 (not shown), and cleans this water whereafter the water is returned to the tank 1 by way of the outlet conduit 18. The advantage of continuous cleaning is that the activity level in the water is kept low while at the same time the time for cleaning the total volume after completed work is considerably reduced. 7. After completed work, the entire contained volume is cleaned. In those cases where cutting methods have been used, the bottom part 9 is possibly slurry-exhausted to capture chips. Then the tank 1 is opened wholly or partially to insert new control rods 3 or other objects. When the scrap stand 20 is full, it is lifted, possibly after flushing, out of the tank 1 and is arranged in a transport flask (not shown) for transport to a storage for ultimate radiactive waste disposal. 8. When no more objects are to be machined, all loose parts, such as tools, are flushed clean and are then lifted out of the tank 1, and then the tank 1 is dismantled. The frame structure 10 is flushed clean and is dismantled as it is being lifted up, the walls 1a-d are also flushed clean as they are being lifted up. The bottom part 9 is slurry-exhausted if necessary. Any final cleaning is carried out in the reactor hall 26 associated with the fuel or reactor pool 2, and the parts are packed for storage or transport. The FIGS. 2-8 of the drawings described in the following show examples of different embodiments of the tank 1 and how this is open or openable for moving objects into/out of the surrounding pool 2. FIG. 2a shows a volume delimitation tank 1 of a woven material which, in order to obtain a well-defined folding of at least the vertical walls 1a-d of the tank, is provided at the manufacturing stage with fold notches 27 at specified intervals. The fold notches 27 can be achieved by weaving in a coarser thread at the notches 27 during manufacture. The tank 1 is formed as a sack with an integrated, possibly stiff square bottom part 9 and with four wall sections 1a-d. Each wall section 1a-d is cut and joined together to the next one such that the walls 1a-d, when being lowered, are folded in a well-defined and predetermined way. From FIG. 2b it is clear that the folding takes place such that every other folded section in a horizontal cross section A--A in one fold increased in the longitudinal direction 1 whereas every other folded section in a horizontal cross section B--B in an adjacent fold increases in the transverse direction t. To control the raising and lowering of the walls 1a-d, loops 29 are provided which run around the support rods 19 which distend the tank 1 at its corner portions. Ropes 30 are connected to at least the uppermost loops 29a to raise the lower the walls 1a-d. The ropes 30 run along the support rods 19 to the beam structure 6 and then along this beam structure to a pulley 30a. The tank in the figure is not entirely distended. The tank 1 is suspended from the beam structure 6 which rests on the edge 5 of the pool. Loops 29 and ropes 30 are preferably made of the same fibres as the walls 1a-d of the tank 1. FIG. 3a shows a tank 1 with walls 1a-d which, as in FIG. 2, are provided with woven-in fold notches 27. In the same way as the tank 1 shown in FIG. 2, this tank 1 is provided with support rods 19 and loops 29 at the corner portions to control the raising and lowering of the walls 1a-d. In the same way as in FIG. 2, ropes 30 are arranged at at least the upper loop 29a in each corner portion for raising and lowering. From FIG. 3b it is clear that when the walls 1a-d are to be lowered, the folding takes place such that every other folded section in a horizontal cross section C--C in one fold is given a larger cross-section area than a horizontal cross section D--D in an adjacent fold. The tank 1 is suspended from the beam structure 6, which rests on the pools' edge 5. FIGS. 4a and 4b show a volume delimitation tank 1 in which at least one wall section 1b is separately raisable and lowerable. This is advantageous for repeated use, whereby not all walls 1a-d need be lowered to move objects in and out, respectively. Depending on the nature of the contamination, point exhaustion can be used during the machining; alternatively, chips can be sucked up from the bottom part 9 after completed work, and it is then not necessary that the whole volume of water be cleaned before lowering the wall portion and moving objects in/out. The non-separately raisable and lowerable walls 1a, 1c and 1d may be made of cloth, fabric or plate, by plate being meant two or more layers of laminate of cloth or fabric, of a suitable fibre. When the walls 1a, 1c, 1d are made of cloth or fabric, support rods 19 are arranged at at least the corners of the tank 1, and preferably also at the upper part thereof. When such a tank 1 is dismantled, the walls 1a, 1c, 1d are allowed to buckle arbitrarily. When the walls 1a, 1c, 1d are made of a stiff plate, they may be provided with fold notches 27, as is clear from FIG. 5, such that the walls can be folded into a suitable size. The separately raisable and lowerable section 1b can either be made of fabric with woven-in fold notches 27, as shown in FIG. 4a, or of fabric or cloth which is rolled off and onto a shaft 28 which may be arranged horizontally or vertically (not shown in the figure). The ropes 30 are adapted to raise and lower the wall section 1b. The ropes 30 run via pulleys 30b to the pulley 30a. One end of the shaft 28 may be provided with a motor (not shown) for rolling on and off. The section 1b runs along the vertical support rods 19a. When the section 1b is arranged in raised position, the tank 1 is sufficiently tight to the surrounding medium. If additional tightness to the surrounding medium is desired, sub-atmospheric pressure of sufficient magnitude is arranged in the tank for the separately raisable and lowerable wall section 1b to fit tightly against the support rod 19a, any leakage being directed inwards towards the contaminated volume. FIGS. 6a and 6b show an embodiment with a sluice 31. The use of a sluice 31 is especially advantageous with repeated use of the tank 1 since the sluice 31 only requires cleaning of a small volume of water when moving objects in and out. The walls 1a-d and the sluice 31 are made of cloth, of fabric, or of a plate. In FIG. 6a, an object is sluiced out by opening the inner sluice-gate 32a, towards the sluice 31, the sluice-gate 32a being preferably made of a stiff plate where the opening takes place by remote operation from the work platform 7. Objects are introduced into the sluice 31 and the inner gate 32a is shut. The water in the slucie 31 is cleaned by means of the cleaning equipment 16 arranged in the tank 1 and the object is possibly flushed before the outer sluice gate 32b is opened towards the pool 2 to pass out the object thereto. If additional tightness to the surrounding medium is desired, sub-atmospheric pressure of sufficient magnitude is arranged in the sluice 31 for the sluice-gates 32a-b to fit tightly. FIG. 6b shows sluice-gates 32a-b made of cloth or fabric, expanded by means of an upper and a lower support rod 19b which, in turned-up position, are substantially horizontal and parallel and which are interconnected, at least at the openable long side, via a substantially vertical support rod 19c. When opening the sluice-gate 32a-b, the support rods 19b are turned down (or up) in the vertical direction by means of a turning device 33 which is remote-controlled from the work platform 7, the cloth surface or fabric surface of the sluice-gate thus being allowed to buckle arbitrarily. As with the sluice design shown in FIG. 6a, sub-atmospheric pressure can be arranged in the tank 1, if additional tightness against the surrounding medium is desired. A suitable way is to ensure that the water level in the tank 1 is lower than in the sluice 31 and that the water level in the pool 2 is higher than in the sluice 31. An additional cleaning device 16 can possibly be arranged in the sluice 31 for continuous cleaning of this volume. The advantage of the design in FIG. 6b is that the sluice takes up little space since the sluice-gates 32a-b are turned downwards (upwards) instead of outwards/inwards. The sluice 31 can be detachably arranged at the tank 1 such that exchange of sluices 31 of different sizes can be made in a simple manner. FIG. 7 shows a tank 1 with five wall sections 1a-e, two of the wall sections 1b and 1e being arranged at least partially to overlap, thus forming a flow passage where a small exchange of water between the water in the tank 1 and the water in the pool 2 is allowed. In those cases where cleaned water is continuously pumped out of the tank 1, such that sub-atmospheric pressure prevails, water will only flow into the tank via the passage, that is, contaminated water does not flow out into the pool 2 via the passage. This tank 1, as the one described in FIGS. 2-6, can be made of cloth, of fabric, or as a plate. In the cloth or fabric design, the walls 1a-e are allowed to buckle arbitrarily when the tank is dismantled. In those cases where the tank 1 is made as a plate, it is provided with fold notches 27, according to FIG. 5, such that the plate can be folded in suitably large sections. The tank 1 according to this embodiment can also be provided with hinges 34, allowing the inner wall section 1e to be turned out and fit tightly against the outer wall section 1b. FIG. 8 shows a tank 1 made with an oval cross section. The tank 1 can also be made with a circular cross section. In both cases it can be designed with or without fold notch 27. The tank 1 is provided with support rods 19, around the vertical support rods 19 there being arranged loops 29, 29a for control of the raising and lowering of the wall 1a. The concept fabric according to the above comprises the traditional way of manufacturing textile fabrics, where a two-thread system with crossing threads, warp and weft is used, but also manufacture by means of, for example, tricot technique or knitting with a single-thread system where a thread forms meshes with itself or with parallel-running threads, or manufacture by means of so-called nonwoven technique where the material is neither woven nor knitted but where loose fibres are bound together in the form of a pile with the aid of glue or chemicals.