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The Nature of Actinide Contaminants
Production operations conducted at Rocky Flats generated a huge volume of wastes contaminated with radionuclides and other hazardous substances. The majority of wastes were shipped off -site for disposal, but many areas at Rocky Flats had contaminated soil and water due to the improper disposal of contaminated materials, ruptured or leaking pipes, fires and explosions, or faulty storage units. Because many of the activities at the plant involved plutonium, much of the contamination was associated with this element. Based on historical data, there were five plutonium accidents and incidents that resulted in the majority of accidental releases of plutonium to the environment. The majority of these drew considerable public concern and media attention.
These releases included a plutonium worker’s worst nightmare: major plutonium glovebox fires in 1957, 1965, and 1969. The 1969 incident occurred when spontaneous combustion of plutonium initiated a fire in Building 776. The fire was drawn through the glovebox line by the glovebox ventilation systems, spreading through several hundred interconnected gloveboxes. Had these fires not been contained within the buildings, they would have threatened contamination of a broad area surrounding Rocky Flats. These incidents brought significant media attention to the Site.
By far the largest source of actinide release to the environment came from improper storage (1958 to 1967) in an open field of about 5,240 55- and 30-gallon drums containing spent machine cutting oil, which was contaminated with plutonium and uranium. It was discovered as early as 1959 that some of these drums were leaking, but the drums were not removed until 1967. Based on material balance around the drums, it is estimated that 5,000 gallons containing approximately 86 grams (5.3 curies) of plutonium were released into the soil. In 1969 some of the contaminated soil was removed and the remaining soil covered with an asphalt cap known as the 903 Pad. During this initial remediation it is believed that winds distributed substantial amounts of contamination to the east and southeast.
Between 1991 and 1999, nearly 2,500 surface-soil samples were collected and analyzed across the Site to assess the level and extent of actinide contamination. A variety of geostatistical analysis tools were used, including variograms (a tool that describes the spatial or the temporal correlation of observations) and kriging (a regression technique to approximate or interpolate data that apply known values in one sample to produce an unbiased estimate of values in another). These are commonly used approaches when small scale concentration distribution is heterogeneous and sample data exist in a large spatial area, such as at RFETS.
Estimated spatial concentrations of plutonium-239 and -240 in surface soil at RFETS were calculated by kriging analysis. Plutonium and americium generally exhibit the same spatial distribution in surface soils, with wide variations in
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In 1969 spontaneous combustion in a glovebox in Building 776 started a fire that spread through the filter plenum.
It is estimated that 5,000 gallons of oil containing 86 grams of plutonium leaked into the soil from these drums improperly stored in an open field. After the drums and some of the contaminated soil were removed, the area was covered with an asphalt cap known as the 903 Pad.
To keep down dust during demolition, water was sprayed on Building 771, dubbed by the media as “the most contaminated building in America.” When demolition of the building was begun in July 2004, Secretary of Energy Spencer Abraham issued a press release that read in part: “This represents a historic milestone in closing Rocky Flats and the most significant cleanup accomplishment to date in the DOE Complex. The demolition of one of the most contaminated buildings in the country, once thought impossible, demonstrates the nation’s commitment to accelerated cleanup and closure of Rocky Flats.”
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