[en] A tomographic method for experimental investigation of the integrity of used LWR fuel has been developed. It is based on measurements of the gamma radiation from the fission products in the fuel rods. A reconstruction code of the algebraic type has been written. The potential of the technique has been examined in extensive simulations assuming a gamma-ray energy of either 0.66 MeV (¹³⁷Cs) or 1.27 MeV (¹⁵⁴Eu). The results of the simulations for BWR fuel indicate that single fuel rods or groups of rods replaced with water or fresh fuel can be reliably detected independent of their position in the fuel assembly using ¹³⁷Cs radiation. For PWR fuel the same result is obtained with the exception of the most central positions. Here the more penetrable radiation from ¹⁵⁴Eu must be used in order to allow a water channel to be distinguished from a fuel rod. The results of the simulations have been verified experimentally for a 8x8 BWR fuel assembly. Special equipment has been constructed and installed at the interim storage CLAB. The equipment allows the mapping of the radiation field around a fuel assembly with the aid of a germanium detector fitted with a collimator with a vertical slit. The intensities measured in 2520 detector positions were used as input for the reconstruction code used in the simulations. The results agreed very well with the simulations and revealed significantly a position containing a water channel in the central part of the assembly