Patent Number: 047770112
Section: summary

The invention relates to a method for checking the dimensions of a nuclear reactor fuel assembly in a water tank, with two mutually parallel probes carrying ultrasonic test heads which are disposed at the free ends thereof, which have acoustic direction directed towards each other and which are movable relative to the fuel assembly, one ultrasonic test head emitting the acoustic waves and the other ultrasonic test head receiving the emitted acoustic waves. Such a method is known from Published European Application No. 0 080 418. In that method the spacing between two fuel rods is determined by means of the pulse/echo method. For this purpose an arm equipped with a transmitting/receiving test head is led past two oppositely situated fuel assembly sides. The echos returning from the fuel rods of the outer row of fuel rods are analyzed in relation to their transit time and provide information on the position of the fuel rods relative to one another or to a normal axis. One of the ultrasonic test heads is used as a transmitter and the other as a receiver, solely as a correction for the temperature-dependent propagation velocity in water. In contrast to this, it is an object of the invention to provide a method and device for checking the dimensions of a fuel assembly for nuclear reactors, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and by means of which the outer contours of a fuel assembly can be measured. With the foregoing and other objects in view there is provided, in accordance with the invention, a method for checking the dimensions of a nuclear reactor fuel assembly in a water tank, with two mutually parallel probes each having a first probe side carrying an ultrasonic test head at a free end thereof with acoustic directions directed towards each other and each having a second probe side facing away from the ultrasonic test head, which comprises transmitting acoustic waves with one of the ultrasonic test heads, receiving the transmitted acoustic waves with the other ultrasonic test head, bringing one of the second probe sides into contact with or placement near a given region of the fuel assembly to be checked, moving the probes towards each other in the direction of the acoustic waves due to contact pressure with the fuel assembly, indicating and assessing or determining the probe movement by a reduction of transit time of the acoustic waves between the test heads, and deriving the actual dimension of the fuel assembly region to be checked while accounting for or considering the dimension of probe movement. A precise measurement of the fuel assembly parts is achieved and damage to the fuel assembly is avoided through the combination of an elastic stop or guide with an indicator of the point in time of contact and of the deflection of the finger of the guide or stop. In order to carry out the method, there is provided a device for checking the dimensions of a nuclear reactor fuel assembly in a water tank, comprising two mutually parallel probes having free ends, first probe sides facing toward each other and second probe sides facing away from each other, ultrasonic test heads each being disposed on a respective one of the first probe sides at the free end of one of the probes, the ultrasonic test heads having acoustic directions directed towards each other, one of the ultrasonic test heads transmitting acoustic waves and the other of the ultrasonic test heads receiving the transmitted acoustic waves, a feeler or sensor disposed on one of the second probe sides, a roller connected to the feeler, means for bringing the roller into contact with a given region of the fuel assembly to be checked causing the probes to be moved closer together in the direction of the acoustic waves due to contact pressure with the fuel assembly, means for indicating and assessing movement of the probes by a reduction of transit time of the acoustic waves between the test heads, and means for deriving the actual dimension of the given fuel assembly region to be checked while accounting for dimensions of movement of the probes. In addition to a gentle treatment of the fuel assembly surface, the roller construction provides the possibility of checking a fuel assembly region for alignment deviations. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a method and device for checking the dimensions of a fuel assembly for nuclear reactors, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.