On January 19, 1993, personnel at the Los Alamos Nuclear Materials Processing-Nitrate Systems Facility (NMT-2) attempted to clear debris from argon flow lines connected to a reaction chamber inside a glovebox. The debris was left over from a previous use of the system. The reaction chamber was used to reduce PuF4 to Pu metal. When the argon flow lines were purged with argon gas, Continuous Air Monitor (CAM) alarms in the room sounded. Personnel evacuated to the corridor outside the room, and health physics staff performed contamination surveys including nose swipes of the eight people who had been in the room. Swipes from two yielded nostril readings of 44 and 997 dpm for one employee (employee A) and 366 and 814 dpm for the other employee (employee B). Health physics personnel placed these two people on "prompt action" urine and fecal sampling programs to evaluate their condition. Final bioassay results were Committed Effective Dose Equivalent (CEDE) doses of 18.0 rem for employee A and 21.0 rem for employee B. Health physics personnel did not find any skin or clothing contamination. (ORPS Report ALO-LA-LANL-TA55-1993-0002, OEWS 93-04, Report of the Type B Investigation of the January 19, 1993 TA-55 Plutonium Intake and Subsequent LANL Actions, U. S. Department of Energy, Albuquerque Operations Office).

Los Alamos National Laboratory (LANL) chartered a Type C investigation was on January 22, 1993. The Type C board issued their final report on April 21, 1994. As a result of the dose estimates developed during the Type C investigation, LANL established a Type B Board of investigation on February 3, 1994. This board issued their final report on May 5, 1994. The final report included a detailed chronology and root cause analysis of the event. The direct causes of the event were inadequate equipment design, and the fact that work being done in preparation for maintenance was performed without hazard analysis or the participation of health physics. In particular, the pre-maintenance work was done without a Special Work Permit or a Radiation Work Permit. However, most of the report dealt with the effectiveness of the intake and dose evaluations and the response to these evaluations. Many of the board findings have generic implications. Personnel failed to comply with the requirements of the LANL Radiation Control Manual (RCM) regarding evaluating intake and dose before returning to work. They also failed to comply with LANL RCM requirements for prompt personnel notification of dose. The board found that compliance with requirements for documentation of radiological counseling, establishment of special control levels, and work restriction requirements was inadequate. As a result, employee B reentered the room less than two hours after the accident to help with decontamination. The following day, after the nasal smears showed positive, employees A and B participated in equipment evaluation and disassembly in the room. A lack of adequate personnel control was shown by the fact that employee B left the facility before all of the internal dosimetry decisions were made. A root cause of all of these problems was a lack of formal guidance for internal dosimetry and its use.

There were also several problems with the use of Continuous Air Monitors. Personnel should have realized that in the event of an acute release, the room monitor would not alarm as quickly as a portable monitor near the point of release. The Operations Center monitor readouts were confusing and not well understood by Operations Center personnel, and the monitoring computer program for interpreting Continuous Air Monitor information was not functional.

These findings illustrate the importance of good equipment design for avoiding accidental releases and of analyzing hazards and taking the proper precautions to avoid accidental uptakes if releases occur. Personnel need to understand the nature of potential releases and the use of portable Continuous Air Monitors to detect them as quickly as possible. Finally, formal guidance and procedures must be followed in the event of a possible uptake to assess the intake and dose and to respond properly to bioassay results.