Patent Number: 048062774
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 An embodiment of the present invention is first described with reference to FIGS. 1a and 1b. In this embodiment, a copper tube 1 to be decontaminated was placed in a water bath 2 and steam blown out from vapor nozzles 5 having an inner diameter of 20A was condensed on the surface of the copper tube 1 so as to decontaminate it. The water bath 2 was filled with a water of 60.degree. C. in temperature and the steam of 100.degree. C. in temperature blown out from the vapor nozzles 5 was condensed by being cooled with the water. The steam was supplied with a pressure of 10 kgf/cm.sup.2 to the vapor nozzles 5 from a vapor supplier 3 via vapor supply piping 4. Since the temperature of the copper tube in the water bath 2 rose when the steam blown out was applied, a cooling liquid was introduced in the copper tube 1 through pipings (M) connected thereto. The steam was jetted from the nozzle 5 with a constant rate of 130 kg/h. In FIG. 1a, "L" indicates a level gauge, "T" being a thermometer, "P" being a pressure gauge, and "F" being a flow meter. FIG. 1b shows a state of steam (S) applied onto the tube 1 to be decontaminated. In addition, since the steam condensed on the surface of the object 1 to be decontaminated became condensed water which raised the level of the liquid in the water bath 2, an amount of liquid corresponding to this rise in level was expelled through an overflow pipe 7. As a result of the decontaminating, it was confirmed that the removal of the surface layer of 38 mg was achieved by the jetting of the steam applied for seven days. This embodiment was also capable of decontaminating a body having complicated surfaces by use of a simple apparatus and of decontaminating hard clads which could not be effectively removed by means of the conventional ultrasonic washing method. Embodiment 2 Another embodiment of the present invention is shown in FIG. 2. In this embodiment, a movable vapor nozzle 5 was moved in piping 8 in order to decontaminate the inside of the piping 8. The vapor nozzle 5 was supported in the piping 8 by supporting means 10 so that the position of the vapor nozzle 5 was suitably maintained and can be moved in the piping 8. The steam having the same conditions as in Embodiment 1 was supplied to the vapor nozzle 5 from a vapor supplier 3 via vapor supply piping 4 which made use of a flexible tube in order to ensure that the steam is properly supplied if the piping 8 is bent along its length. Since the steam condensed on the inside of the piping 8 became condensed water which increased the amount of water in the piping 8, surplus water was expelled through a vent pipe 9. In addition, since the temperature of the liquid in the piping 8 rose when the steam blown out was condensed, the outside of the piping 8 was cooled by a cooling apparatus 6 or the rise in the temperature of the water in the piping 8 was controlled to be a temperature not more than saturation temperature by continuously supplying cooling water from a drain pipe 11. In addition, since the vapor nozzle 5 was simply inserted in the piping 8, the piping did not need to be detached contrary to the case of the ultrasonic washing method, and could thus be decontaminated in situ. Furthermore, the decontaminating work could be conducted extremely simply and efficiently. Embodiment 3 A further embodiment of the present invention is shown in FIG. 3. This embodiment concerns decontamination of the inside of a bath 1 which is an object to be decontaminated by vapor nozzles 5 provided in the bath 1. The vapor nozzles 5 had an arrangement and a structure both of which correspond to the shape of the inside of the bath 1 to be decontaminated so as to supply steam to the inside of the bath 1 with an appropriate distribution pattern. The steam having the same conditions as the Embodiment 1 was supplied to the vapor nozzles 5 from a vapor supplier 3 via vapor supply piping 4 and was blown out therefrom. Since the steam condensed on the inside of the bath 1 became condensed water which increased the level of the water in the bath 1, surplus water was expelled through an overflow pipe 7. In addition, since the temperature of the water in the bath 1 rose when the steam blown out was condensed, part of the surplus water was guided to a cooling apparatus 6, was cooled, and was then returned to the bath 1, whereby the temperature of the water in the bath 1 was controlled to be a temperature not more than the saturation temperature. In this embodiment, in order to control the vibrations of the vapor nozzles 5, the vapor nozzles 5 were preferally fixed to the bath 1 by a supporting means 10. In the embodiment of the present invention shown in FIG. 1, it is possible to recover the washing water remaining after condensation and to recycle it. In other words, if the washing water is reused after being returned to the vapor supplier 3 by recovery piping 7 which extends from the overflow pipe 7 and is again vaporized, the amount of secondary waste solution produced following the decontamination can be reduced. Of course, the washing water remaining after condensation can be returned to the vapor supplier 3 from the vent pipe 9 shown in FIG. 2 or from the overflow pipe 7 shown in FIG. 3 by way of recovery piping 7a. In the present invention, an organic solvent may, for example, be used as the liquid in which the object to be decontaminated is placed. In addition, the above-described liqid becomes more effective if it is kept at a lower temperature. It is particularly preferable to cool the liquid to its saturation temperature or less because the vapor will then easily condense on a solid surface. EFFECT OF THE INVENTION In accordance with the present invention, the following effects are obtained: (1) Hard clads in the depths of an object to be decontaminated can be removed. In particular, in a nuclear installation, since the greater part of a radiation source is contained in these hard clads, their removal can greatly reduce the amount of exposure to which personnel are subjected during work tasks. (2) The soundness of piping and instruments is not impaired after decontamination. (3) The amount of secondary waste solution produced following the decontamination work is very small and it can be reduced to an extremely small amount, depending upon the manner of the operation of the method employed. (4) The safety level during decontamination work is high and a sanitary working environment can be maintained. (5) A body having a complicated surface form can be decontaminated and the inside of piping and instruments can be decontaminated in situ. (6) It is possible to suppress the spread of radioactive contamination following the decontamination work.