Patent Number: 044252960
Section: summary

FIELD OF THE INVENTION The present invention relates to probe-holding apparatus for a probe for checking steam generator tubes. BACKGROUND OF THE INVENTION It is necessary for the water tubes of vertical steam generators used in nuclear power plants to be periodically checked. In this respect, the water constituting the primary fluid and contaminated by the nuclear reactions must not be able to pass into the secondary fluid which is used for operating a turbo-alternator. This check is made with the aid of a Foucault current probe which is passed through each of the tubes. A slit or hole in the tube or even a simple reduction in its thickness is then converted into a variation in the output current from the probe. In practice, the probe is carried by an apparatus mounted movably in the lower chamber of the generator, into which all the tubes open. This apparatus carries a guide tube which is brought in front of a tube of the bundle and into which the probe is inserted. After checking a tube, the probe is withdrawn from the tube, the apparatus is moved through a distance equal to the distance between two tubes, and the probe is inserted into a new tube. These various operations are controlled from the outside because as the chamber wall has been in contact with irradiated water, it itself emits ionizing radiation. The probe-holding apparatus proposed hitherto comprises expansible mandrels which are inserted and fixed into the tubes of the bundle. However, with such apparatus, it is often difficult to check those tubes disposed at the bundle periphery. Moreover, any given apparatus is suitable only for checking tubes which are a given distance apart. If it is required to check the tubes of a steam generator in which the tube pitch is different, the apparatus has to be considerably modified. Finally, such apparatus is large and bulky. OBJECT OF THE INVENTION An object of the present invention is to provide a probe-holding apparatus for checking steam generator tubes, which does not have these drawbacks. SUMMARY OF THE INVENTION According to the invention, there is provided a probe-holding apparatus for a probe for checking steam generator tubes, said apparatus comprising a telescopic arm resiliently urged towards its position of maximum extension and said arm having first and second opposed ends, a support, joint means movably mounting the first end of the arm on the support, and a carriage hinged to the second end of the arm, said carriage comprising guide means for a probe, drive means, and a stepping motor for driving the drive means, said drive means including spaced projections, the guide means for the probe and the projections being disposed in the same direction, and the projections being spaced apart from each other by a distance related to the pitch of the generator tubes. Further according to the invention, there is provided a probe-holding apparatus for a probe for checking steam generator tubes, said apparatus comprising a telescopic arm having first and second opposed ends, support means, said first end being pivotally mounted on the support means, and a carriage mounted on the second of said ends, said carriage comprising guide means for the probe, an endless drive member, an array of projections spaced along the drive member in the direction of drive and engageable in the ends of the tubes, and stepping motor means for driving the drive member. Having placed the apparatus in one of the end chambers of the steam generator, the probe-holding carriage is kept resting by the arm against the tube plate located in this chamber, the projections being engaged in the generator tubes. The probe guide means is then located in front of another generator tube which can then be checked. The stepping motor is then started, this enabling the carriage to be moved over the tube plate in a precise manner and enabling the probe guide means to be brought in front of another tube of the generator. By retracting the telescopic arm through a small distance the projections are disengaged from the tube plate, this enabling the carriage to be rotated with the aid of the arm in order to move the projections and the probe guide means into a different direction. After returning the carriage into contact with the tube plate, the tubes lying in this direction can be checked. As the carriage drive motor is a stepping motor, the carriage movements can be recorded, and thorough knowledge can be had of the tube being checked at any moment. The stepping motor can be an electric, pneumatic or hydraulic motor, which drives the carriage by way of a transmission.