A methodology for gamma ray spectrometric determination of fission rates in fuel specimens

A methodology was developed to determine the fission rates of compact fuel specimens using high resolution gamma ray spectrometry, which has been extended to fuel specimens of various dimensions. The absolute efficiency data were generated from the activities of the fission products and the gamma ray activity of 238U at 1001 keV. Axial profiles of the gross gamma activity of the fission products were generated using NaI(Tl) detector using discrete scanning and automated fuel pin scanner. Axial profiles of the neutron flux along the 600 mm length of the irradiation position was also measured using Cu as a flux monitor. The measured fission rates were compared with the values obtained from the neutron flux measurements. Applicability of this methodology for cooling periods as long as 210 d, was also demonstrated by obtaining the fission rates from the measured activities of long-lived fission products like 103Ru (39.25 d), 95Zr (64.03 d) and 144Ce (284.6 d). (author)