Accurate identification of frames into concrete reinforced walls in a nuclear power plant was required because of maintenance labours. Several cuts in the concrete, including the frame, were planned. The cutting lines were designed to avoid as much as possible the frame bars. To perfom this work the ground penetrating radar has been used. The use of ground prenetrating radar techniques allow to determine the vertical and horizontal position of the frame bars. GPR detects also other reflectors in to the walls. The ele ctric propertie s contrast betw een the concrete and th e steel o f the frame gives reflections clearly detected in the records. This near surface study requires to use high resolution antennas with a very high center frecuency. The measurement precision required In the work was obtained using a special marker to carry the antenna, specially design for this job. The marker allows to know the position of the antenna on the wall with a precission of centimeters. The measurements were acquired from one antenna with a center frecuency of 1000 MHz, with a SIR 10 system of Geophysical Survey Sistems Inc.. An experimental test made in a scale model help to the interpretation of the records.. A later and careful treatment in laboratory, using all the records obtained in the nuclear power plant, applying vertical lowpass and highpass filters and horizontal lowpass filter was perfomed, to place correctly the bars into the concrete
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