High Level Tritiated Water Monitoring by Bremsstrahlung Counting Using a Silicon Drift Detector

The β-ray induced X-ray spectrometry (BIXS) is a promising technique to monitor the tritium concentration in a fuel cycle of a fusion reactor. For in-situ measurements of high level tritiated water by bremsstrahlung counting, the characteristics of a low-noise silicon drift detector (SDD) have been examined at the Tritium Laboratory Karlsruhe (TLK). In static measurements with constant sample volume and tritium concentration, the bremsstrahlung spectra of tritiated water samples in a concentration range of 0.02 to 15 MBq/ml have been observed. The volume has been kept constant at 5 cm³. The observed spectra are well above the noise threshold. In addition to X-rays induced by β-rays, the spectra feature X-ray fluorescence peaks of the surrounding materials. No indications of memory effects have been observed. A linear relation between the X-ray intensity and the tritium concentration was obtained and the lower detection limit of the setup has been determined to 1 MBq ml^-1, assessed by the Currie criterion. In addition, the spectra obtained experimentally could be reproduced with high agreement by Monte-Carlo simulations using the Geant4-toolkit. It was found that the present detection system is applicable to non-invasive measurements of high-level tritiated water and the SDD is a convenient tool to detect the low energy bremsstrahlung X-rays.