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DUF6 Health Risks
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A discussion of depleted UF6 cylinder storage activities and associated risks.

Management Activities for Cylinders in Storage

The long-term management of the existing DUF6 storage cylinders and the continual effort to remediate and maintain the safe condition of the DUF6 storage cylinders will remain a Departmental responsibility for many years into the future. The day to day management of the DUF6 cylinders includes actions designed to cost effectively maintain and improve their storage conditions, such as:

  • General storage cylinder and storage yard maintenance;
  • Performing regular inspections of cylinders;
  • Restacking and respacing the cylinders to improve drainage and to allow for more thorough inspections;
  • Repainting ends of skirted cylinders and repainting cylinder bodies as needed to arrest corrosion; and
  • Constructing new concrete cylinder storage yards and reconditioning existing yards from gravel to concrete to improve storage conditions.

Health Risks from Cylinder Storage

Under normal conditions, the main risk from cylinder storage is to cylinder yard workers from exposure to low-level external radiation in the vicinity of cylinders. The radiation levels measured on the outside surface of filled depleted UF6 storage cylinders are typically about 2 to 3 millirem per hour (mrem/h), decreasing to about 1 mrem/h at a distance of 1 ft (0.3 m). The radiation exposures of the workers are carefully monitored and limited to stay well under applicable guidelines and regulations. Appendix D of the PEIS reports that the historical dose to cylinder yard workers has been less than 200 mrem annually, much less than the regulatory limit of 5,000 mrem/yr and less than the DOE administrative control limit of 2,000 mrem/yr for workers. (For more details on risks from continued storage, see also Appendix D of the PEIS.)

Once depleted uranium has been converted from UF6 to a more stable form such as uranium oxide or UF4, the risk associated with accidents during storage and handling is greatly decreased because of the reduced chemical reactivity and solubility of the conversion products compared to UF6. The PEIS evaluated long-term storage of uranium oxide. Under normal operating conditions at an oxide storage facility, there would be a small increase in cancer risk for workers due to exposure to external radiation from the uranium oxide; however, good work practices would minimize the exposure and the risk. Even under extreme accident conditions, such as if a storage facility building were damaged in an earthquake, the risk of immediate chemical injury to the general public and to workers from exposure to released uranium oxide would be small.