Developments in gamma scanning irradiated nuclear fuel

Abstract

Non-destructive methods, based on high-resolution gamma-ray spectroscopy, have been further developed for on-site measurements of several nuclear fuel parameters and efficient verification of the fuel in-pile performance. The measuring system is based on a high-purity germanium detector (HPGe) together with suitable fast electronics and an on-line PC data aquisition module. Measurements have been carried out in the fuel storage pools of several LWR plants by the ABB Atom Company for more than 10 years. Special computer codes for evaluation of the spectroscopic data and detailed comparison with core physics evaluations have been developed. Techniques have been employed for determination of fission gas release (FGR), showing good correlation with destructive post-irradiation examinations (PIE) using mass spectrometry. Axial cesium redistribution which gives a control on local temperature history (possibly overheating), axial burnup profiles, burnup comparison between fuel rods and examination of the fuel rods with respect to their integrity are other applications. Relative axial power distribution, using gamma radiation from 140La, can be determined with a precision of ±1% for a single rod node measurement. It is concluded that this high-resolution gamma scanning technique that has been developed is a very versatile measuring method. It rapidly gives information about several physical processes in the fuel, with the possibility of feedback to reactor operators.