Handling tritium irrevocably leads to tritium-contaminated surfaces. Tritiated tools, measuring instruments, and equipment will continuously release tritium from their surfaces, predominantly as HTO, even if the original exposure was to T2 gas. Decontamination is an essential and continuous activity of any tritium facility striving to mitigate contamination spread throughout and beyond the facility. Washing with surfactants either by hand or in ultrasonic baths, purging with moist air, high-temperature thermal desorption, and isotopic exchange are common decontamination techniques. Both washing and purging yield large quantities of low specific activity water or increased emissions when the water is not collected. High-temperature thermal desorption generates less tritiated water but the technique is not always practical or feasible. Cleaning tritiated surfaces with low-temperature plasmas offers an alternative solution that minimizes the generation of secondary waste and finds broader applicability.This paper reports the efficacy of removing tritium from contaminated metallic samples using a low-pressure, two-temperature plasma driven by an RF generator. Prevailing plasma electronic and ion temperatures were characterized using Langmuir field probes. The measured tritium recovery rate-profiles indicate the presence of at least three mechanisms: triton diffusion from the metal bulk towards the surface, diffusion through the oxide layer that naturally forms on metal surfaces, and finally, surface desorption from the oxide layer responsible for tritium transport from the bulk to the plasma. These transport mechanisms are observed to operate on different time scales. Tritium removal efficiencies are reported for a range of neutral gas density conditions and different gases. The results will be compared against a simple model based on Fickian diffusion through the bulk and the oxide layer.

Absorption and transport of tritium in metals

242nd National Meeting (2011)

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