Non destructive gamma spectrometric determination of the fission products activities rations in the reactor RA used fuel element

An elaborate nondestructive gamma spectrometric method for determination of fission product activity ratios, used in the fuel element burn-up measurement, is described. It consists in the self-consistent used-fuel gamma spectrum analysis, in which all the needed data, including spectrometer efficiency, energy calibrations and absorbtion corrections, are taken from one and the same gamma spectrum, measured with a Ge(Li) spectrometer system. A well positioned cylindrical collimator defines the analysed part of the fuel element. Results of the experimentally obtained and analysed long lived fission products spectra in the energy range between 400 and 2200 keV of the used reactor RA fuel element (2% enriched natural uranium) are given. The fuel was irradiated between two and three years and cooled for 340 and 1819 days