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Characterization of Carbon Tritide Particles in a Tokamak Fusion Reactor

Yung Sung Cheng, Yue Zhou, Charles A. Gentile, Charles H. Skinner

Fusion Science and Technology / Volume 41 / Number 3P2 / May 2002 / Pages 867-871

Material Interaction and Permeation / Proceedings of the Sixth International Conference on Tritium Science and Technology Tsukuba, Japan November 12-16, 2001

Amorphous tritiated carbon films are formed through co-deposition of the radioactive isotope tritium (3H or T) with carbon onto plasma facing surfaces in fusion plasmas. The Tokamak Fusion Test Reactor (TFTR), operated by the Princeton Plasma Physics Laboratory, was fueled by tritium and deuterium neutral beam injection and gas puffing. Tritium was co-deposited as amorphous hydrogenated carbon onto graphite tiles and stainless steel surfaces inside the reactor. Since termination of plasma operations, carbon tritide particles have remained in the air in the vessel. Dosimetric limits for occupational exposure to carbon tritide particles need to be established. The purpose of this study was to characterize carbon tritide particle samples inside the TFTR in terms of size, self-absorption of tritium beta, and dissolution rate in simulated lung fluid. Dose estimates of the inhaled carbon tritide particles can be calculated based on the dissolution rate, particle size, and self-absorption factor. The count median diameter and geometric standard deviation were 1.23 µm and 1.72, respectively, indicating that they are respirable particles and can stay suspended in the air for a longer time. The dissolution rate in the lung-simulated fluid was determined in a static system. The dissolution rate ranged from 10−1–10−3 per day in the first few hours, then it decreased to between 10−3 and 10−4. The retention curve of tritium in carbon indicated that >90% of the tritium remained in the particles after 110 d in the simulated lung fluid. This information is being used to support the establishment of respiratory protection requirements.

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