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The understanding of helium and tritium diffusion in irradiated beryllium is a fundamental step in validating and improving the existing models of swelling due to helium bubbles and of tritium retention. High-precision measurements of the release rate of helium and tritium from weakly irradiated beryllium pebbles have been carried out by a Knudsen-cell technique: the samples are heated in high vacuum up to temperatures above the melting point and gas release is measured by mass spectrometry. The evolving of gas diffusion and release modes up to the complete release of the gas inventory can be followed. A minor part of the helium content is released by atomic diffusion to free surfaces between 700 and 1400 ?K, most of it precipitates into bubbles and is released only as a consequence of their abrupt venting, starting above 1400 ?K. Tritium effusion appears to be affected by surface recombination phenomena; a small fraction of tritium is trapped in helium bubbles.

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Additional information

Authors: RABAGLINO E, Forschungszentrum Karlsruhe (DE);SCAFFIDI-ARGENTINA F, Forschungszentrum Karlsruhe (DE);RONCHI C, European Commission, Joint Research Centre, Institute for Transuranium Elements, Karlsruhe (DE)
Bibliographic Reference: An oral report given at: 10th International Conference on Fusion Reactor Materials (ICFRM-10). Organised by: Forschungszentrum Klarlsruhe. Held in:Baden-Baden, 14-19 October 2001.
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