Confirmatory Survey Results for the Reactor Building Dome Upper Surfaces, Rancho Saco Nuclear Generating Station Page: 3 of 17
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surface activity measurement with hand-held radiological instrumentation, SMUD chose to perform
in situ gamma spectroscopy measurements of the dome surfaces (SMUD 2006b). The detector
geometry for the dome survey was defined as a 28 square meters (m2) circular plane with a source to
detector distance of 3 meters (m). Each individual circular plane, also designated as the field-of-view
(FOV), was designated at a grid or measurement location.
SMUD used site-specific supplemental DCGLs for Co-60 and Cs-137 for determining surface
release criteria (SMUD 2006a and b). ORISE judgmentally selected five grid blocks for confirmatory
surveys based upon final status survey (FSS) results which approached unity.
Beta surface scans were performed using hand-held gas proportional detectors coupled to ratemeter-
scalers with audible indicators. Surface scans were performed on up to 80% of the judgmentally
selected grid block surfaces. Particular attention was given to cracks, joints, and horizontal surfaces
in the evaluated structural surfaces where material may have accumulated.
Direct measurements for beta activity were performed at 31 (a minimum of five locations within
each grid) locations on the evaluated structural surfaces which were available for confirmatory
survey activities. Smear samples were collected at three direct measurement locations of elevated
surface activity within Grid CRC052 to determine removable activity levels at these locations. Direct
measurements locations are indicated on Figures 3 through 7.
Interlaboratory Comparison Soil Samples
At the request of the NRC site representative, ORISE was tasked with conducting an interlaboratory
comparison to evaluate the quality of the licensee's radioanalytical procedures. Therefore, ORISE
reviewed RSNGS characterization soil sample data and selected seven soil samples, collected and
analyzed by SMUD, for interlaboratory comparison analyses. These samples were shipped by
SMUD personnel and received by ORISE laboratory personnel on July 10, 2006.
SAMPLE ANALYSIS AND DATA INTERPRETATION
Radiological data and sample media were returned to the ORISE laboratory in Oak Ridge, TN for
analysis and interpretation. Radioassays were performed in accordance with the ORISE Laboratory
Procedures Manual (ORISE 2006b). Soil samples were analyzed by gamma spectroscopy for the
primary radionuclides-of-concern [ROC (i.e., Co-60 and Cs-137)]. However, spectra were also
reviewed for additional gamma-emitting fission and activation products associated with the RSNGS
and other identifiable total absorption peaks. Soil sample results were reported in units of picocuries
per gram (pCi/g). Dry smear samples were analyzed for gross alpha and gross beta activity using a
low-background gas proportional counter. Smear results and direct measurements for total surface
activity were converted to units of disintegrations per minute per 100 square centimeters
(dpm/100 cm2).
FINDINGS AND RESULTS
Reactor Dome Surface Activity Measurements
Beta surface scans identified several areas of elevated beta activity on the horizontally positioned
metal bracket. The brackets previously connected air conditioning ductwork to the inside surface of
the reactor building walls. Beta surface scans did not identify elevated beta activity on the vertical1695\Reports\2006-10-25 Confirmatory Survey Results
Rancho Seco Nuclear Generating Station
2
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Adams, Wade C. Confirmatory Survey Results for the Reactor Building Dome Upper Surfaces, Rancho Saco Nuclear Generating Station, report, October 25, 2006; Oak Ridge, Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc881506/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.