Tritium accumulation and ozone decontamination of tungsten and beryllium

TL;DR

This study uses the TRACE chamber to investigate tritium surface contamination on Be and W and to assess in-situ ozone-based decontamination, with and without UV irradiation. Be accumulates tritium much more rapidly than tungsten, while decontamination by ozone without UV shows no clear advantage, indicating that UV irradiation is required for effective removal. The results highlight material-dependent adsorption and the potential limitations of ozone-only decontamination for fusion-relevant surfaces, informing future system upgrades to explore UV/ozone synergy under more realistic conditions. The planned enhancements, including high-temperature operation and direct UV exposure, aim to translate in-situ decontamination concepts into scalable, technically feasible strategies for tritium handling facilities and fusion devices.

Abstract

Tritium adsorption on surfaces creates a variety of issues, ranging from the fields of fusion applications to small and large-scale laboratory experiments using tritium. The extent to which tritium accumulates on surfaces is generally material-dependent and must be determined through experiments. Additionally, this surface contamination necessitates the implementation of appropriate decontamination procedures, preferably in-situ. A suitable method could be exposure to ozone during UV irradiation. However, it is currently not known if both components are necessary for the decontamination. At Tritium Laboratory Karlsruhe, both questions on contamination and decontamination can be addressed using a single experimental setup. With this, it is possible to expose solid samples to gaseous tritium to measure the temporal activity evolution. Furthermore, the system can be filled with dry air, and dry air containing ozone to explore their decontamination effect. Both measurement modes were applied to beryllium and tungsten samples, which were chosen for their relevance in fusion. The beryllium surface was observed to accumulate tritium more than four times faster than tungsten when exposed to gaseous tritium. Concerning the decontamination, without simultaneous UV irradiation, exposure to ozone did not have any distinct effect on the surface activity compared to simply using dry air. This leads to the conclusion that UV illumination of the surfaces is required to achieve a significant decontamination factor.

Figures (5)

• Figure 1: SEM images of the beryllium (a) and tungsten (b) samples.
• Figure 2: Increase of surface activity of three beryllium samples due to repeated exposure to gaseous tritium.
• Figure 3: Surface activity evolution of the tungsten sample.
• Figure 4: In-situ decontamination of the third beryllium sample with the corresponding pressure during exposure.
• Figure 5: In-situ decontamination of the tungsten sample.