Results of analyses performed on concrete cores removed from floors and D-ring walls of the TMI-2 reactor building

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The March 28, 1979 loss-of-coolant accident at Three Mile Island Unit 2 (TMI-2) exposed about 7200 m/sup 2/ of concrete surfaces within the Reactor building to liquid and vapor-phase contaminants. The majority of those surfaces are protected by coatings of epoxy-based, nuclear grade paints. during September 1983, seventeen high quality cores were extracted from the concrete floors and D-ring walls ar the 305- and 347-ft elevations of the Reactor Building. The samples were subjected to a series of analyses to determine the surface concentrations of radionuclides present and to characterize their distribution in the coatings layer and sub-surface concrete. The analysis results indicate the protective coatings provided significant protection against radionuclide penetration. Radiocesium, in most cases, was found to be confined within a few millimeters of the top surface of the coatings layer. However, at floor locations having coatings that were damaged prior to the accident, radiocesium penetrated into the sub-surface concrete to a depth of several centimeters. Parametric calculations performed using the ISOSHLD-2 computer code indicate that the decontamination of the 347-ft elevation floor will reduce the general area gamma exposure rates at this elevation by as much as 40%. The data indicate that scabbling would be an effectivemore » decontamination technique.« less