Tritiated water detection in the 2.17 µm spectral region by cavity ring down spectroscopy
Résumé
Nuclear waste containers are intended to be stored in dedicated disposals sites. For the inside and environmental safety of the disposals site, the tiny outgassing rates leaking out the containers are measured. The radioactive HT gas is actually measured by liquid scintillation, however an alternative method, cavity ring down spectroscopy, is currently developed for tritium measurement in its oxidized form HTO and evaluated. The HTO molecule concentration is determined by the measurement of spectroscopic parameters from transitions on its harmonic 21 (R) transitions between 4590 and 4600 cm-1. Two tritiated water standards are measured with a dedicated CRDS set-up. Compared to the theoretical database, the line positions are correct (-0.067 to -0.128 cm-1), their relative intensities is in agreement with the database, but their absolute intensities are 30% weaker. Among the seven intense lines, the 4596.485 cm-1 line (intensity 8.22 10-22 cm/molecule) and the 4592.407 cm-1 line (intensity 9.83 10-22 cm/molecule) are isolated and intense for a sensitive detection. The HTO detection limit with the present set-up is 3 kBq (10 min), equivalent to 1.8 1012 molecules in the 111 cm3 CRDS cell. This detection limit could improve by a factor 3 (at least) by reducing the detection noise.
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