Non-destructive method by gamma sampling measurements for radiological characterization of a steam generator: Physical and numerical modeling for ANIMMA (23–27 June 2013)

The radiological characterization of a steam generator consists of evaluating the global radiological activity in the tube bundle. In this paper, we present a non-destructive method and the results analysis of the gamma sampling measurements from a sample of U-tubes in the bundle. On site, the implementation of the methodology is fairly easy. But the analysis of the results is more complicated due to the long path of the gamma ray (from ⁶⁰Co quite penetrating), and also the heterogeneous activity of U-tubes bundle, which have not the same life cycle. We explain why the periodic spatial arrangement complicates also the analysis. Furthermore, we have taken into account the environment of all tubes measured because of all the external influence activity of others U-tubes (the nearest, the most distant and potential hot spot). A great amount of independent influence coefficient had to be considered (roughly 18 million). Based on a physical and numerical modeling, and using a Cholesky algorithm solving the problem and saving time machine.