A METHOD TO QUANTIFY TRITIUM INSIDE WASTE DRUMS : 3He INGROWTH METHOD

This method enables an indirect, non intrusive and non destructive measurement of the Tritium activity in wastes drums. The amount of tritium enclosed inside a wastes drum can be determined by the measurement of the leak rate of 3 He of this latter. The simulation predicts that a few months are necessary for establishing the equilibrium between the 3 He production inside the drum and the 3 He drum leak. In practice, after one year of storage, sampling 3 H eoutside the drum can be realized by the mean of a confining chamber that collect the 3 He outflow. The apparatus, the experimental procedure and the calculation of tritium activity from mass spectrometric 3 He measurements are detailed. The industrial device based on a confinement cell and the automated process to measure the 3 He amount at the initial time and after the confinement time is described. Firstly, reference drums containing a certified tritium activity (HTO) in addition to organic materials have been measured to qualify the method and to evaluate its performances. Secondly, tritium activity of organic wastes drums issued from the storage building in Valduc have been determined. Results of the qualification and optimised values of the experimental parameters are reported in order to determine the performances of this industrial device. As a conclusion, the apparatus enables the measurement of an activity as low as 1 GBq of tritium in a 200 liters drum containing organic wastes.