On September 24, 1993, workers at the Pantex Plant exceeded the plutonium mass limits while loading a magazine, thus violating the facility operations inspection standard. Prior to the event, the Nuclear Material Control Room (NMCR) operators incorrectly specified the amount of plutonium to be loaded into the magazine, and workers subsequently overloaded the magazine by 17 kilograms (kgs). The error was identified approximately four and one half hours later when a clerk entering the serial numbers of the plutonium units into the computerized accountability system (CRADS), identified that the limit of 30 kgs was exceeded. At the time of the overload, the CRADS system required the use of the unit serial number in order to make a data entry, and the unit serial numbers were not available to control room personnel until the units were off-loaded. Upon discovery of the overload condition, workers relocated the units to other authorized locations within the 24-hour limiting condition of operation specified in the Safety Analysis Report. Facility personnel stated that there was no criticality concern because of the sealed geometrically safe container design for the plutonium. They stated that the magazine could be fully loaded with plutonium containers, totally flooded with water, and there would be no concern from a criticality perspective.
Preceding the event, the NMCR shift manager was not available and the operators provided the off-loading instructions to the workers without the shift manager's oversight. The operators apparently misread the chart that lists the administrative limits and related the erroneous information to the workers. Facility personnel implemented several compensatory measures pending development of permanent corrective actions. These measures included issuance of a directive to begin pre-assignment in the CRADS of locations for weapon and component receipts, revision of operating procedures to detail steps to complete receipt transactions in the CRADS, and a requirement that, until all personnel are adequately trained, a senior supervisor will be physically present when assignments and receipts take place. (ORPS Report ALO-AO-MHSM-PANTEX-1993-0051)
A similar event occurred at the facility on February 2, 1993, when, during weapon off- loading operations, workers exceeded the high-explosives limits and the plutonium limits specified in the operations and inspections standard. Facility personnel identified the root cause as failure to provide workers with pertinent information regarding high-explosive limits and plutonium mass limits. They failed to conduct a pre-job briefing to transmit this information. Contributing factors identified by facility personnel included (1) the procedures did not specify that a transportation supervisor needed to be present at all times during the loading and unloading operations, (2) the logistic plans for the weapons movements were not required by the procedure, (3) there was no training provided on the contents of the operations and inspections standard, and (4) there was no one person in control of the operation. (ORPS Report ALO-AO-MHSM-PANTEX-1993-0008)
These events emphasize the importance of attention to detail, close supervision of critical work activities, procedural compliance, comprehensive training, and good communication techniques. Preplanning involving the movement of weapons should include considerations for effective communication and an understanding of high explosive and plutonium limit allowances. In addition, the September 24, 1993, event also illustrates the risks associated with using only one method for verification of a safety parameter. Reliance on only the CRADS system was the only method used by the operators for ensuring compliance with the plutonium mass limits.