Patent Number: 047626712
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the invention will now be described with reference to the drawings. In FIG. 3 an injection device main body 40 is suspended within the downcomer 8 by means of a wire rope 52 that hangs from above a refuelling platform 41 provided above the RPV 1. Reference numeral 43 indicates a suspension mechanism (for example a winch). The injection device main body 40 is constructed as shown in FIG. 4 and FIG. 5. Reference numeral 44 in the drawings indicates a casing. This casing 44 is shaped approximately as a rectangular box, whose face 45 facing the RPV 1 matches the internal shape of the RPV 1 and which has a longitudinal groove 46 formed in the middle thereof and extending over the entire height of the face 45. This groove 46 corresponds in position to a sample mounting bracket 20 that is mounted on the RPV 1. The groove 46 enables the injection device main body 40 to be lowered without interferring with this bracket 20. The bottom end of the casing 44 is arcuate so as to match the shape of the upper surface of thermal sleeve 15. Thus, the injection device main body 40 is automatically positioned by seating on the thermal sleeve 15. A pair of slit-shaped injection nozzles 47 and 48 are mounted at positions facing each other on the left and right at the bottom end of casing 44. Water is supplied to the injection nozzles 47 and 48 from a water feed pipe 49 arranged within the casing 44 and connected to the injection nozzles 47 and 48. This water feed pipe 49 is connected to a water feed unit, not shown, disposed on the refuelling platform 41. A plurality of electromagnets 50 are mounted on the face 45 of the casing 44 opposite the RPV 1. The inside surface of the RPV 1 is covered with a lining (not shown) of austenitic stainless steel, which is non-magnetic. This lining is normally about 5 mm thick. It has been thought that since this lining is made of non-magnetic steel, it would be impossible to fix any appliances to it by electromagnetic force. However, from the experimental results of FIG. 6, it was found that since the matrix of the RPV 1 is low alloy steel, a sufficient attractive force for the injection device can be obtained. FIG. 6 shows the results of measuring the attractive force of the electromagnets 50 in the case of an austenitic stainless steel lining (thickness 5 mm) and a low alloy steel RPV matrix. The designations ".phi.90 mm" and ".phi.80 mm" in the figure indicate the diameter of the respective electromagnetic coils. In this embodiment, the attraction between the injection device main body 40 and the RPV 1, due to the electromagnets 50, is sufficient to withstand the reaction produced when high pressure water is introduced from the injection nozzles 47 and 48. As shown in FIG. 5, an underwater television camera 51 and underwater lights 52 are arranged on the injection device main body 40. In fact two underwater lights 52 are provided, one on each side of the underwater television camera 51. The relative positions etc. of the injection device main body 40 and thermal sleeve 15 etc. can be observed using the underwater television camera 51 and the underwater lights 52. As shown in FIG. 4, a pair of touch sensors 53 are mounted at the bottom end of the casing 44. These can be used to ascertain when the injection device main body 40 is seated on the thermal sleeve 15. A further pair of touch sensors 54 are mounted on the surface of the casing 44 facing the RPV 1. These sensors 50 can be used to ascertain when the casing 44 has been attracted onto the RPV 1. As shown in FIG. 7, the injection outlets of the injection nozzles 47 and 48 are in the form of slits running along the length of the aperture formed by the annular gap 17, which extends around the thermal sleeve 15. Alternatively, the injection outlets may consist of a plurality of circular outlets which are arranged in an arcuate row along the length of the aperture formed by the annular gap 17. As shown in FIG. 8, the injection nozzles 47 and 48 are mounted so as to make a positive radial or dip angle of 0.degree. to 45.degree. with respect to a cylindrical plane concentric with the axis of the inlet nozzle 13 and directed toward this axis. The mode of operation of the device constructed as above will now be described. First of all, the injection device main body 40 is lowered from refuelling platform 41 using the wire ropes 42 into a position immediately above the recirculation inlet nozzle 13 into which the high-pressure water is to be introduced. Thus the injection device is suspended between the branch pipes 16 of the jet pumps 12 and the RPV 1. Its position is checked using the underwater television camera 51, the underwater lights 52 being switched on for this purpose. If the device is lowered to the location where the bracket 20 is mounted on the RPV 1, it is adjusted so that the groove 46 of the casing 44 is aligned with the bracket 20. Thus the injection device main body 40 is lowered until it is seated on the thermal sleeve 15. Seating of the injection device main body 40 can be ascertained remotely by means of the touch sensors 53. Current is then passed through the electromagnets 50 to cause the injection device main body 40 to be attracted to the RPV 1. This attraction operation is remotely monitored using the touch sensors 54. High-pressure water is then introduced into the annular gap 17 through the injection nozzles 47 and 48, either to remove accumulations of radioactive substances in this annular gap 17, or to effect forced cooling during IHSI. Different flow configurations within the annular gap 17 result from different mounting positions of the injection nozzles 47 and 48 in the circumferential direction of the recirculation inlet nozzle 13, and these will now be explained with reference to FIG. 9 to FIG. 11. These figures were obtained by experimental observation of the flow configuration in the annular gap 17 of thickness 5 mm in a recirculation inlet nozzle 13 of bore 287 mm. FIG. 9 shows the case wherein the mounting positions of two adjacent nozzles 47 and 48 are spaced by not more than 7.5.degree. from a vertical plane passing through the center axis of recirculation nozzle 13 and wherein both the injection nozzles 47 and 48 are operated simultaneously. In this case, the two jet flows have a cooperative guiding effect on each other which causes the jet flow to penetrate to the furthest recesses of the anular gap. Next, FIG. 10 shows the case wherein the mounting positions of the two adjacent nozzles 47 and 48 are separated so as to be spaced by more than 7.5.degree. from a vertical plane through the center axis, both the injection nozzles 47 and 48 being operated simultaneously. In this case, the two jet flows are dispersed in the central region of the annular gap 17 and bounce off each other, so the jet flow energy is lost, and the jet flows do not reach the most interior region of the annular gap 17. This gives rise to a stagnant region 55 in the most interior portion of annular gap 17. With such a nozzle arrangement, it is therefore more effective to operate the injection nozzles one at a time, rather than operating them both simultaneously. That is, if water is injected from only a single injection nozzle 48, the jet flow can then reach the innermost portion of annular gap 17, as shown in FIG. 11. In the case of cleaning the annular gap 17, since the amount of water delivered by the injection nozzles 47 and 48 can be adjusted remotely, such adjustment can be performed while monitoring the diminution in radiation dosage, and in the case of carrying out IHSI, adjustment can be performed while monitoring the temperature of the recirculation inlet nozzle 13. The amount of water delivered per injection nozzle is suitably 0.2 m.sup.3 /h. A device constituting a further embodiment of this invention for introducing high-pressure water onto the inside surface of a jet pump instrumentation nozzle 22 will now be described with reference to FIG. 12 and FIG. 13. Internal instrumentation piping 60 constituted by a plurality of pipes is arranged in the jet pump instrumentation nozzle 22, forming a narrow gap 61 between the piping 60 and the inside of jet pump instrumentation nozzle 22. An injection device main body 70 for introducing water into this gap 61 has practically the same construction and action as the injection device main body 40 of the previous embodiment. However, since the jet pump instrumentation nozzle 22 is smaller than the recirculation inlet nozzle 13, the casing 71 is smaller, and the bottom end of the casing 71 is formed with bifurcated portions 72 which straddle the entire internal piping 60. In this case, since electromagnets 73 can be provided in both bifurcated portions 72, there is the advantage of improved stability of the coupling between the casing 71 and the inside wall of the RPV 1. The construction of the touch sensor and the injection nozzles, etc. (not shown) is the same as in the previous embodiment. The injection nozzles 47 and 48 can be strings of small circular pores instead of slits. The following advantages are obtained by the embodiments described above. (i) Water can be introduced remotely into the interior of the vessel nozzles (the recirculation inlet nozzle 13 and the jet pump instrumentation nozzle 22) that are in not easily accessible positions at the lower part of the RPV 1. Thanks to the fact that the injection device main body 40 or 70 is accommodated in a casing 44 or 71, having a face 44 or 71 opposite the RPV 1 which is of a shape matching the RPV 1 and having the groove 46, and thanks to the fact that operation can be continually monitored using an underwater camera 51, fitting or removal of the device and introduction of high-pressure water can be performed while being able to realiably prevent interference with reactor structures, particularly the bracket 20. (ii) Since the bottom end of the casing 44 is arcuate and of the same shape as thermal sleeve 15 of the recirculation inlet nozzle 13, or since the bottom end of the casing 71 is bifurcated so that the internal piping 60 of the jet pump instrumentation nozzle 22 can be inserted between the bifurcations, the injection device main body 40 or 70 can be located in position simply by seating the casing 44 or 71 on the thermal sleeve 15 or the internal piping 60. Thus complicated construction or operations for the purpose of locating are entirely unnecessary. (iii) Thanks to the provision of the touch sensors 53 and 54 on the casing 44, the injection device main body 40 can be monitored using these touch senors 53 and 54, so the device can be operated with ease and in a reliable manner. (iv) High-pressure water can be effectively introduced into the annular gap 17 or the gap 61 thanks to the fact the injection outlets of the injection nozzles of 47 and 48 of the present embodiment are slit-shaped or shaped as strings of small pores and are symmetrical from left to right and are set at dip angles of 0.degree. to 45.degree., and thanks to the fact that fluid is injected simultaneously from one or more injection nozzle mounting positions in the circumferential direction of recirculation inlet nozzle 13 or the jet pump instrumentation nozzle 22. (v) The flow amount of high-pressure water can be set to a value of 0.2 m.sup.3 /h or more; water can be introduced while monitoring the cleaning effect or the progress of IHSI; and water can be effectively introduced into the annular gap 17 or into narrow and not easily accessible spaces. (vi) Since fixing of the injection device main body 40 is by means of a simple electromagnet 50 construction, complication of the device and therefore complicated operational procedures can be effectively avoided. Obviously, numerous (additional) modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.