On August 30, 1993, three workers at the Los Alamos National Laboratory TA-55 plutonium processing facility received internal plutonium contamination while preparing equipment for decontamination and decommissioning. The three and 10 other individuals were in a room when a continuous air monitor (CAM) alarmed. All personnel were immediately evacuated, surveyed, and given nasal smears. Positive nasal smears ranging from 27 to 309 dpm were measured for the three workers who had received internal contamination. No contamination was found on any other individuals. (ORPS Report ALO-LA-LANL-TA55-1993-0033)
Facility personnel suspect the source of the contamination was residual plutonium fluoride gas in an unpressurized argon line to a glovebox. The gas was released when a technician, while disconnecting electrical equipment, loosened a bolt that was common to both the electrical equipment and a block valve in the gas line, dislodging the valve. The technician was wearing standard personnel protection clothing, surgical gloves, and booties.
After the evacuation, Radiological Control Technicians (RCTs) wearing Self Contained Breathing Apparatuses entered the room to perform surveys collect the CAM air filters. Surface contamination levels of 40,000 dpm/100cm2 were measured in the vicinity of the block valve and the highest CAM filter reading was 6,690 dpm per cubic meter of air. Later, a technician and two RCTs entered the room, removed the valve, and plugged the end of the tubes.
As a result of the event, facility management issued a stand-down order on September 1 that suspended activities while work control systems were evaluated. The order directed that all future work at TA-55 be performed under approved operating procedures, work packages, and radiation work permits, and listed the management system elements necessary to accomplish compliance with the directive.
In previous Operating Experience Weekly Summaries (OEWS) the Office of Nuclear Safety reported other internal contamination events at TA55. On April 8, 1993, two technicians received internal doses of 26 and 13 millirem when they dropped an assembly with two small cylinders of 827 mCi tritium-argon gas while removing it from a 30-gallon drum, causing one of the cylinder fittings to leak (ORPS Report ALO-LA-LANL-TA55- 1993-0009). On January 19, 1993, nasal smears ranging from 44 to 997 dpm alpha were taken from two workers who were contaminated as they attempted to clear debris from argon flow lines connected to a reaction chamber inside a glovebox at the Nitrate Systems Facility (ORPS Report ALA-LA-LANL-TA55-1993-0002). In OEWS 93-35, NS also reported an event at the Weldon Springs Site where on July 28, 1993, bioassay results indicated that ten subcontractors performing remediation activities received internal uranium contamination (ORPS Report ORO--MK-WSSRAP-1993-0025).
These events underscore the added importance of work control and planning when performing activities with a higher-than-normal potential for personnel internal contaminations, such as remediation, decontamination and demolition.