Combination of chemical separation and data treatment for 55Fe, 63Ni, 99Tc, 137Cs and 90Sr/90Y activity determination in radioactive waste by liquid scintillation

Routine operations involving nuclear reactors and decommissioning activities require numerous chemical analyses. Most of the procedures developed for these chemical characterisations involve several separation steps to prepare the sample for measurement. Chemical treatments are time- and manpower-consuming, labour intensive and produce significant quantities of waste. In order to address this problem, we evaluate a data treatment procedure (multivariate calibration-PLS), which we propose as a substitute to some of these separation steps. Mixtures of beta emitter radionuclides of increasing complexity (90Sr/90Y-99Tc, 90Sr/90Y-99Tc-63Ni-137Cs and 90Sr/90Y-99Tc-63Ni-137Cs-55Fe) have been measured by liquid scintillation (LS) counting. The influences of quenching and level of activity was evaluated and the activity of unknown samples determined. Despite the spectra overlapping and low resolution of LS, relative errors in the activities quantification of unknown samples inside the range covered by the calibration matrix are lower than 15% whatever the number of radionuclides included in the solution was.