Lesson Learned Statement:Excess moisture on a systems high efficiency particulate air (HEPA) filters may allow migration of radioactive contamination through the filters. Engineered systems need to be in place, to ensure moisture build-up is minimized. Any changes, even temporary, to the operational parameters must be incorporated into operator round sheets used to monitor plant conditions. It is also important that even temporary changes (not only physical changes) are incorporated into plant procedures. Further, personnel needs to understand the interaction of environmental changes along with changes in operational parameters during initial design and later modifications.
Discussion:At approximately 1050 hours on 11/13/01, unexpected contamination was discovered by a Radiological Control Technician while performing surveys during routine work. Upon further investigation, more dispersed spots of radioactive contamination were discovered outdoors (on the ground and roof areas) surrounding the Waste Tank Farm (WTF), Vitrification Facility, and the Fuel Receiving and Storage (FRS) area. Two distinct deposition patterns were delineated and correlated to both activities that were taking place in the WTF Facility and ambient weather conditions. The contamination is believed to have come from the WTF, through the ventilation system and ultimately, out of the Main Plant stack.
Analysis:It is believed that the deposition, to the north of the Main Plant Facility, happened in the early morning hours of September 26, 2001. Increased moisture had been introduced into the ventilation system by tank transfers and waste removal operations. This increased moisture, coupled with operational ventilation system changes and prior component failures, led to excess moisture on the system HEPA filters. Contamination then migrated through the filters, out the ventilation system and ultimately out of the stack. Weather conditions at this time facilitated contamination falling back to earth and spotting the ground and surrounding structures.
The second deposition, southeast of the Main Plant Facility, apparently happened on October 7, 2001. Residual contamination from the first event was still in the dead legs of the ventilation system redundant blower. This blower was started for the first time since the previous event, and similar weather conditions caused the contamination to again spot the ground and surrounding facilities. There was no personnel contamination or uptake as a result of this event. In addition, there were no environmental National Emission Standard for Hazardous Air Pollutants (NESHAP) release issues. Contamination spread was limited within the site boundaries. Decontamination activities took place to physically remove most of the contaminated spots.
Originator:West Valley Nuclear Services Company, Ed Lachapelle (716) 942-2117
Validator:Joe Marek (716)942-4370
Contact:Joe Marek (716)942-4370
Name Of Authorized Derivative Classifier:N/A
Name Of Reviewing Official:N/A
Priority Descriptor:Yellow / Caution
Keywords:HEPA filters; MOISTURE
References:Occurrence Report Number OH-WV-WVNS-WVNSGEN-2001-0005
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DOE Function / Work Categories:Conduct of Operations - Work Control
Conduct of Operations - Work Planning
ISM Category:Perform Work
Hazard:Personal Injury / Exposure - Radiation / Contamination
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