Tritium accumulation and ozone decontamination of tungsten and beryllium

TL;DR

This study investigates tritium accumulation on tungsten and beryllium surfaces relevant to fusion, and evaluates ozone and UV-based decontamination methods, finding UV irradiation essential for effective tritium removal.

Contribution

It provides experimental data on tritium accumulation rates and demonstrates that UV irradiation is necessary for ozone-based decontamination of these materials.

Findings

Beryllium accumulates tritium faster than tungsten.

Ozone alone does not significantly decontaminate surfaces without UV.

UV irradiation enhances the effectiveness of ozone in decontamination.

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.