Patent Number: 
Section: description

Shown in FIGS. 1 and 2 are two embodiments of the inventive device, differing from each other by the fact that the device shown in FIG. 1 defines an open circuit for the transportation of a cleaning fluid, while the device shown in FIG. 2 defines a closed circuit for said transportation. The device is arranged for the removal of a radioactive deposition from a fuel assembly 1 in a nuclear plant. For this purpose, the device comprises a container 2 accommodating the fuel assembly 1. Moreover, it comprises first means 3, 4, 5 which are arranged to feed a fluid into and through the container 2, the fluid being provided to release the deposition from the fuel assembly 1 by means of abrasion, and transport the radioactive deposition material thus released out of the container 2. The device also comprises second means 6, 7 which are arranged to receive the radioactive material transported out of the container 2 by the fluid. These second means 6, 7 thereby comprise a filtering device 6 by which a filter is arranged to separate the released radioactive material from the fluid. Moreover, they comprise a tube conduit 7 extending from the container 2 to the filter 6 and arranged for the transportation of the fluid and the released, radioactive material. The first means 3, 4, 5 comprise a feeding funnel 3 for solid particles, here ice particles, a first pump 4 in which the solid particles are mixed with a liquid, here water, and a second pump which pumps the liquid to the first pump 4. The first pump 4 is thereby arranged to suck into it the solid particles that are fed from the feeding funnel 3. The device is arranged in a basin 8, which is filled with a xcex3-radiation-dampening medium, here water. In particular, the container 2 which accommodates the fuel assembly 1, and the second means 6, 7 are arranged at a considerable depth in order to avoid any larger amount of radiation, mainly gamma radiation (xcex3-radiation), from leaking out from the basin via the liquid surface 9. According to FIG. 1, the second pump 5 providing the first pump 4 and the container 2 with liquid is connected to an external liquid source. Thereby, also the second means 6, 7 are connected, via a conduit 11, to an arrangement or the like (not shown) for the reception of the liquid fluid that has passed the filter 6 and thereby been separated from radioactive material. Accordingly, an open circuit exists. However, in the embodiment according to FIG. 2, the second pump 5 is connected to the filter 6 via a conduit 12, the pump 5 being arranged to pump the liquid which has passed through the filter 6 back to the first pump 4 and the container 2. Accordingly, FIG. 2 describes a closed system. It should however be mentioned, that the closed circuit according to FIG. 2, at least after having been used for a certain time, requires some kind of liquid draining as the provision of solid particles which then melt and form a liquid phase results in a continuous increase of the amount of liquid in the circuit according to FIG. 2. The first pump 4 is also arranged to suck into it a gas, in this case air, which then, together with the mixture of water and solid articles, is pumped into and through the container 2. Preferably, the first pump 4 is arranged to suck into it the gas and the solid particles. The fluid, thus comprising a liquid, here water, a gas, here air, and solid particles, here ice, is pumped into and through the container 2 which encloses the fuel assembly 1 which in its turn, in a way known per se, comprises a plurality of cladding tubes for nuclear fuel. Thanks to the effect of the gas (amongst others), giving rise to turbulence, a relatively rapid flushing through the container 2 can take place, with an abrasive action on the crud deposit which is present at the outside of the cladding tubes. Above all, loose crud is removed, and, for operational technical and economical reasons, this treatment should go on for a period as short as possible in order to make it possible to put the fuel assembly 1 into operation as soon as possible. Thereby, basin 8 is other than the basin in which the fuel assembly is arranged during operation. The time of treatment is approximately 15 minutes or less. The device also comprises means 14 arranged to transmit infrasounds towards the fuel assembly 1. Those means 14 suitably comprise an infrasound source of a conventional sort and are only schematically shown in FIGS. 1 and 2. Moreover, the fuel assembly 1 is rotatably arranged in the container 2, and the device comprises a member 15, here a schematically shown motor, arranged to rotate the assembly 1. The rotational axis of the fuel assembly 1 thereby coincides with the longitudinal axis thereof. The device also comprises means 16, schematically shown in FIG. 1 and 2, arranged to heat at least a part of the fluid which is fed into the container 2. The means 16 are preferably arranged to periodically heat the water which is delivered to the container 2. Suitably, when a flow of hot water into the container 2 is generated, no ice is fed into the fluid. In order to obtain a treatment time which is as short as possible, a suitable mixture of liquid, solid particles and gas needs to be guided into the container 2. During the treatment of a boiling water reactor assembly, the flow of liquid should be approximately 10-50 kg/s, preferably 15-35 kg/s and most preferably 20-25 kg/s. For a pressure water reactor assembly, the corresponding amounts are 50-200 kg/s, 75-150 kg/s, and 100-125 kg/s. Approximately 1 kg air is added for each 20 liter of liquid, here water. The ice flow is approximately 30-70% of the liquid flow. The amount of ice added is preferably as low as possible within this interval, and, if possible, even lower. The size of the solid particles, that is the ice particles, is in the range of 5xc3x975xc3x975 mm. Of course, a plurality of variants and embodiments will be obvious for the man skilled in the art without thereby leaving the very scope of the invention. The invention is also to be defined only by what is stated in the appended claims, the drawing and the rest of the description.