Speaker
Description
Low level tritium measurement has become a critical challenge for environmental monitoring. As environmental tritium concentrations have continuously decreased since the peak following the nuclear tests of the 1950s and 1960s, environmental monitoring laboratories must adapt their analytical methods to meet this new challenge. Using direct measurement, the performance of standard liquid scintillation counters is no longer sufficient to achieve the minimum detection limit (0.3 Bq/L) required for some samples. In 2025, the French Nuclear Safety and Radiation Protection Authority (ASNR) analyzed approximately 2000 samples of water for 3H measurement, of which 30 % had result below the detection limit. To increase the proportion of significant results while maintaining the ability to process large numbers of samples, an alternative approach had to be found. Electrolytic enrichment has proven to be an effective solution in many hydrology laboratories and already in some environmental monitoring laboratories. Its relevance has further increased given the recent upgrades made possible by proton exchange membrane (PEM) technology.
Because tritiated water has a slightly higher binding energy than H2O water molecules, electrolysis can be used to selectively enrich tritium. After a few hours of electrolysis with PEM cells, the sample volume decreases while the concentration of tritiated water increases. The detection of low activities of tritium is then possible with standard liquid scintillation counters. To find the initial activity, an enrichment factor (EF) must be applied. To determine it, the most commonly used approach consists of measuring tritium standards before and after electrolytic enrichment in order to calculate a cell-specific value that can be applied to unknown samples. However, it is also possible to use the enrichment of the deuterium. In this work, a new method for deuterium measurement using ICP-MS rather than laser spectrometry will be presented. Electrolytic enrichment is a robust and reliable technique, enabling the laboratory to achieve detection limits below 0.3 Bq/L with two days of enrichment.
This presentation will outline the comprehensive 3H monitoring strategy currently employed at ASNR. It will then introduce the electrolytic enrichment method currently developed at ASNR, highlighting the installation and use of the PEM cell, as well as the challenges encountered in achieving the targeted performances. Finally, a description of the EF determination will be presented, comparing the spiked method and the deuterium method.