Poor design of local exhaust hood leads to radioactive release in the work area.

At a U.S. Department of Energy (DOE) waste handling facility, transuranic waste contained in standard 208-L (55-gallon) drums was being prepared to meet the DOE's Waste Isolation Pilot Project Waste Acceptance Criteria. During a particular waste handling operation, it was necessary for the workers to open several 208-L drums with TRU waste and prepare the waste to meet the WIPP Waste Acceptance Criteria. This operation was performed while the waste drums where positioned adjacent to a drum ventilator, which was designed to capture emissions generated from the drums during waste handling activities. During this activity, the continuous air monitor alarmed and reached an instantaneous air concentration of 0.1 Bq m(-3), or a factor of 300 times higher than the derived air concentration for inhalation class W 239Pu. The DOE conducted an investigation to determine why the drum ventilator did not control the transuranic emissions and to evaluate possible improvements to the drum ventilator and exposure controls. By adding upper and lower flanges to the drum ventilator, the capture velocity was increased by 88% without increasing the fan's speed. Adding flanges is a simple and inexpensive modification that enhances the performance of the drum ventilator. In addition to a poor design, the drum ventilator's capture velocity was compromised by competing air velocities that were generated by waste handling activities.

Derivation and implementation of an annual limit on intake and a derived air concentration value for uranium mill tailings.

Monitoring workers and work areas at the Department of Energy Uranium Mill Tailings Remedial Action Project sites is complex because all radionuclides in the 238U and 235U decay chains may be present in an airborne uranium mill tailings matrix. Previous monitoring practices involved isotopic analysis of the air filter to determine the activity of each radionuclide of concern and comparing the results to the specified derived air concentration. The annual limit on intake and derived air concentration values have been derived here for the uranium mill tailings matrix to simplify the procedure for evaluation of air monitoring results and assessment of the need for individual monitoring. Implementation of the derived air concentration for uranium mill tailings involves analyzing air samples for long-lived gross alpha activity and comparing the activity concentration to the derived air concentration. Health physics decisions regarding assessment of airborne concentrations is more cost-effective because isotopic analysis of air samples is not necessary.

Evaluation of in vitro dissolution rates of thorium in uranium mill tailings.

Dissolution rates of thorium from the uranium mill tailings piles at two Department of Energy Uranium Mill Tailings Remedial Action Project (UMTRAP) sites have been evaluated. The thorium dissolution rates were evaluated in vitro using simulated lung fluid. The former uranium mills at the UMTRAP sites employed different chemical processes (acid leach and alkaline pressure leach) to extract the uranium from the ore, and the thorium dissolution rates at these sites were found to be markedly different. A site specific annual limit on intake (ALI) value for 230Th was calculated for the UMTRAP site that was associated with a multiple component dissolution curve.

Evaluation of the beta energy spectrum from a distributed uranium mill tailings source.

The beta energy spectra from uranium mill tailings, 90Sr with different absorber thicknesses, and a uranium metal slab were measured and compared to select an appropriate beta source for calibrating a personal dosimeter to measure shallow dose equivalent when exposed to uranium mill tailings. The measured beta energy spectrum from the 90Sr source, with a 111 mg cm-2 cover thickness, was selected as a possible calibration source for a personnel dosimeter. The dose equivalent rate to the skin at 1 cm from a distributed tailings source of infinite thickness, with a 226Ra activity of 56 Bq g-1 (1.5 x 10(3) pCi g-1), was measured to be 0.024 mSv h-1 (2.4 mrem h-1).

Uranium in vitro bioassay action level used to screen workers for chronic inhalation intakes of uranium mill tailings.

A uranium in vitro bioassay (urinalysis) action level was derived for use at the Department of Energy's Uranium Mill Tailings Remedial Action Project sites to identify chronic inhalation intakes of uranium mill tailings causing 0.5 mSv (50 mrem) annual effective dose equivalent. All radionuclides in the 238U decay chain that contribute 1% or more to the annual effective dose equivalent from an inhalation intake of uranium mill tailings were included in the derivation of the urinalysis action level. Using a chronic inhalation intake model, the uranium urinalysis action level for a 24-h urine sample, collected on a quarterly schedule, was calculated to be 1.5 micrograms.