On November 4, 1993, personnel responding to a glovebox overheat detection system supervisory alarm at Rocky Flats Building 707 observed a one-liter stainless steel can containing plutonium oxide moving erratically. The can was stored on an overheat detection storage tray in the glovebox where the alarm originated. After continuing intermittently for approximately two hours, the movement subsided when the can came to rest against the side of the storage tray. The supervisory alarm also became intermittent while the can was moving and ceased when the can stopped moving. Facility personnel characterized the can contents in August 1993 and determined that it contained approximately 180 grams of a mixture comprised of about 7 percent (corrected for moisture content) plutonium metal fines and 93 percent plutonium oxides. Glovebox oxygen concentration and differential pressure remained at normal levels throughout the incident, and at no time was there an indication of an overheat condition in the glovebox. (ORPS Report RFO--EGGR-PUFAB-1993-0175)
Facility personnel, taking a conservative approach and assuming an oxidation reaction may have occurred and might still be possible, immediately curtailed operations in the affected module and posted the area as requiring respiratory protection. They also cordoned off the affected glovebox and established a dedicated fire watch to maintain visual contact with the glovebox. Site personnel then developed an action plan and associated operations orders to provide step-by-step instructions and specify required management oversight for investigative actions related to the moving can. The first part of the plan provided detailed guidance for inspection of the can contents to attempt to determine if an oxidation reaction occurred. The second part of the plan involved investigation of the glovebox storage tray vibrations and associated supervisor alarms.
Facility personnel completed the first part of the plan on November 5 when they (1) visually inspected the can and removed it from its storage location; (2) weighed the can; (3) vented, removed the lid, and inspected the contents of the can; and (4) replaced the lid and returned the can to its storage location. The results of these activities indicated that an oxidation reaction did not occur. There was no physical deformation or other evidence of an oxidation reaction on the external surfaces of the can; the weight increase associated with a reaction was not observed (weight decreased 0.3 grams); and the oxide and internal surfaces of the can did not deviate from the expected color or texture. Investigators also determined that the supervisory alarms were caused by a wiring short aggravated by movement of the can.
As of this writing, facility personnel had not determined what caused the can to move but were continuing the investigation. However, this event provides a good example of a conservative, thorough, detailed, and safe response to a detected abnormal condition. The event also underscores the need for contingency plans that can expedite responses to known potential scenarios. ONS will provide additional information on this event in future OE Weekly Summaries as warranted.