Gamma scanning in in-service inspection of nuclear fuel burnup

A gamma scanning method is being developed for determining fuel element burnup. The Nuclear Research Institute has concentrated on expressing gamma radiation self-absorption in the fuel pin material. The absorption coefficient was measured for UO2 of a different density in variation with energy. It is shown that the UO2 absorption coefficient amounts to approximately same values as that for lead. Also determined were the absorption coefficient of zirconium whose size is comparable to that of molybdenum and the relative efficiencies of semiconductor detectors. All constants necessary for the determination of burnup of the WWER type ceramic fuel are thus known. An instrument was also developed for radial gamma scanning used in measuring fission product radial distribution. A collimator with an adjustable collimator slot is a unique part of the instrument. (O.K.)