1. Field of the Invention
The present invention relates to a foreign matter recovering apparatus for recovering a small foreign matter present in a space inaccessible by an operator and, in particular, a space of fuel assembly for nuclear power generation.
2. Description of the Related Art
It has been generally known to use, for example, a magic hand and forceps as a means for recovering foreign matter trapped in a narrow space. Further, it has also been known to use, as means for recovering a foreign matter trapped in a normally inaccessible or hard-to-access space, a medical endoscope for immediately eliminating foreign matter by a biopsy forceps as well as a vacuum for vacuum-sucking foreign matter by a nozzle from a distant location.
The endoscope is guided into the human body cavity to photograph the interior of the internal organs of a human being or remotely controlled from outside the human body to remove its diseased region by the forceps so that a diagnostic treatment is made from within the human body.
In nuclear power generation, use is made of a fuel assembly 201 as shown in FIG. 19. The fuel assembly 201 is comprised of pipe-like fuel elements 202, . . . filled with nuclear fuel and has a full length of, for example, about 4 m with clearances 203, . . . of, for example, 2 to 3 mm created among the respective fuel elements 202, . . . . FIG. 19 shows the fuel assembly comprised of 8.times.8 fuel elements.
In FIG. 19, reference numerals 204 and 205 show upper and lower tying plates, respectively. The fuel elements 202, . . . are held, by the upper and lower tying plates 204 and 205, at their upper and lower end portions.
In FIG. 19, reference numeral 206 shows a plurality of spacers (only one of them is shown) disposed in a longitudinal direction of the fuel elements 202 such that they are held partway in the longitudinal direction of the fuel elements 202, . . . . The spacer 206 includes a mechanism for individually holding the fuel elements 202, . . . .
External springs 207, . . . are disposed between the upper ends of the fuel pairs 202 and the upper tying plate 204.
The fuel assembly 201 is held, prior to use, for example, in a fuel storage pool 208 as shown in FIG. 20, and suspended at a water depth of about 10 m.
Further, the fuel assembly 201 may be temporarily held in the storage pool 208 in the event of a nuclear reactor failure, etc., so that it is inspected for its defect. Therefore, the fuel assembly can be held in the pool not only before its use but also at any necessary time during its use.
In the case where foreign matter, such as screws and metal pieces, is trapped in the fuel assembly 201 in the pool 208, it is necessary to recover it, but the fuel assembly 201 is suspended in the storage pool at the water depth of 10 m under a high pressure environment where there exits radiation of high intensity. The clearances 203 among the fuel elements 202 are each created on the order of as small as 2 to 3 mm.
It is, therefore, not possible to immediately recover such foreign matter by hand. It is required that the means for recovering the foreign matter be remotely controlled at a position adequately spaced apart from the fuel assembly 201.
It may be considered that the aforementioned endoscope is applied to the recovery of the foreign matter in the fuel assembly 201. The medical endoscope can be directly operated, while viewing the foreign matter through an eyepiece, in which case the instrument is remotely controlled at an operation distance of, for example, about 1 m. The control of the instrument direction, driving of the forceps, etc., are done with the use of an operation force transmitted through a flexible wire. Further, the endoscope is usually so set to have 5 mm in external diameter.
It is, therefore, difficult for the endoscope to recover a small foreign matter at a position adequately remote from the fuel assembly 201, that is, to guide the instrument's tip into the fuel assembly 201 and set it there, guide the instrument's tip or forceps into the clearance 203 of the fuel elements 202, and accurately drive the forceps and recover the foreign matter.
For a means for vacuum-sucking a foreign matter without a visual inspection, it is difficult to accurately locate its vacuum nozzle at a predetermined position of an object of interest.