Patent Number: 045171521
Section: claims

1. The method of testing spaced fuel element tubes which are assembled in bundles to form a reactor core by ultrasonic energy, wherein an ultrasonic transmit transducer and an ultrasonic receive transducer are moved through open spaces between the tubes and when testing a tube are disposed with a tube in the space between said transducers, said transmit transducer when in position for testing a tube being energized to cause ultrasonic energy to propagate in said tubing and the resulting revolving echo signal being received by said receive transducer and if occurring within a predetermined gated time interval (12) being passed to an evaluation means, the improvement comprising: determining anew for each tube to be tested the start of said gated time interval (12) by measuring the transit time value (T.sub.L) of ultrasonic signals traversing the distance from said transmit transducer (4) to said receive transducer (5) when said transducers are in the open space between the last tested tube and the next to be tested tube, and  subtracting a constant value (C) from the transit time value (T.sub.L), said constant value (C) being selected to cause the transmitted ultrasonic signal (DE) received during the transit time measurement to fall just outside said gated time interval (12).