At Saclay, we have a new gamma-ray spectrometry facility located in the immediate proximity of the OSIRIS reactor core. This device is used to examine nuclear fuel elements in loop or rig throughout the period of irradiation, with no more than a few minutes required to transfer the fuel from the irradiation point to the measurement bench. Thus, we are able to follow the evolution of a large number of fission products in space and time with particular reference to short half-life radionuclides.This internal reactor gamma-ray spectrometry device of original design eliminates corrections for radioactivity decrease and avoids any risk of overlooking relevant data.