Removal of deuterium retained in boron powders by bakeout

Dust formation and accumulation is recognized as a potential operational and safety issue in fusion devices [1]. Associated hazards include higher chemical reactivity, toxicity, accumulation of activation products, and tritium retention [2]. Dust can accumulate on plasma facing components, between or behind tiles, or in ducts. With boronization as one of the current leading technologies for wall conditioning, the implications of boron (B) dust accumulation must be understood. In this work, we evaluate the fuel retention properties of B dust. For this, we exposed B powders to neutral molecular deuterium (D) gas (as a proxy for tritium) to mimic the gas exposure of particles that are out the plasma line-of-sight. The D₂-exposed powders were baked at different temperatures (423 to 723 K) and times (0 to 3 days) to assess how chamber bakeouts can remove any trapped fuel from particulate B. We used temperature programmed desorption (TPD) to evaluate D retention following powder bakeout. Our results show low D removal efficiency when the bakeout is performed at temperatures below 523 K. Complete D removal was achieved within 10 minutes at 723 K. The use of oxygen or hydrogen environments during bake out significantly improves the deuterium removal efficiency.

[1] S. Rosanvallon, et al., J. Nucl. Mater. 1, 390-391 (2009). [2] K.A. McCarthy, et al., FT, 34(3P2), 728-732 (1998).