Activated carbon filtration of organic and ammonia vapors from underground single-shell tanks

The US Department of Energy has 149 underground single-shell waste storage tanks located on the Hanford Site in south-central Washington State. The single-shell tanks (SSTs) have capacities ranging from 208 to 2,785 m{sup 3} (55,000 to 1,000,000 gal) and contain radioactive and chemical wastes that were generated at the site. Each SST is equipped with a high-efficiency particulate air (HEPA) filter. The purpose of the HEPA filter is to reduce radionuclide emissions from a tank to acceptable levels. Most SSTs are passively ventilated through the HEPA filter during atmospheric pressure fluctuations. Organic, ammonia, and other toxic vapors exist in some SSTs that, when emitted from a tank, may pose hazards to personnel. Therefore, emissions from these tanks may need to be filtered or diluted to reduce potentially harmful vapors to acceptable concentrations outside the tanks, thus ensuring a safe work environment. An activated carbon filtration system was designed and is being tested on SST 241-C-103, a tank known to contain organic and ammonia vapors.