Results of nondestructive methods for nuclear fuel burnup determinations are presented. It is shown that in an experimental irradiation (wellthermalized neutron spectrum, small fuel samples, and relatively short irradiation time), the results obtained by high resolution gamma spectrometry are in agreement with those derived from the application of the solid-state track detectors technique and neutron dose measurements. The importance of the experimental errors is due mainly to the poor knowledge of the fission yields.