A numerical method to improve the reconstruction of the activity content in homogeneous radioactive waste drums

摘要

Segmented y-scanning (SGS) is the most widely applied technique to non-destructively reconstruct the isotope specific activity content in radioactive waste drums. Around 25% of all radioactive waste drums at the Forschungszentrum Jiilich exhibit a homogeneous matrix distribution and activity distribution. Due to these conditions, a numerical method is derived, which largely enhances the accuracy and reliability of the activity reconstruction in comparison to the common analytical method by avoiding various simplifications in the calculations. The numerical method is validated with GEANT4 simulations of reference drums containing the isotopes ~(137)Cs and ~(60)Co. The activities, which are reconstructed with the numerical method in waste matrices with a density range from 0.5 gem~(-3) to 2.3 gem~(-3) show systematic deviations of around - 2.1 % and 4.0% in case of ~(137)Cs and ~(60)Co, respectively. These results show a significant improvement in accuracy compared to the analytical method revealing systematic deviations of around 14.8% and 23.2%, respectively. These results are confirmed by the reconstruction of the activity content in a reference drum from SGS measurements. Uncertainties calculated in the numerical method are halved in comparison to the analytical method. Thus, the reliability of the reconstructed activities is enhanced.