Confirmatory Survey Results for the Reactor Building Dome Upper Surfaces, Rancho Saco Nuclear Generating Station Page: 4 of 17
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concrete surfaces of the Reactor Building Dome walls. Total net beta activity measurements
ranged from -13,000 to 410,000 dpm/100 cm2. Removable activity measurements ranged from
9 to 26 dpm/100 cm2 for alpha and 230 to 890 dpm/100 cm2 for beta. Surface activity level results
are presented in Table 1.
Interlaboratory Sample Analyses
Prior to shipping, SMUD re-analyzed the seven soil samples selected by ORISE. The analytical
results for the comparative evaluation of the RSNGS characterization samples are provided in
Table 2. The results indicate that the quality of the SMUD laboratory data, within the parameters of
sample preparation and analytical procedures, were comparable with ORISE's analytical results.
COMPARISON OF CONFIRMATORY SURVEY RESULTS AGAINST THE RELEASE CRITERIA
The major contaminants identified by SMUD at RSNGS are beta-gamma emitters-fission and
activation products-resulting from reactor operation. Cesium-137 and Co-60 have been identified
during characterization as the predominant radionuclides present on structural surfaces. SMUD
developed site-specific DCGLs (which have yet to be approved by the NRC) based on dose
modeling not to exceed 25 mrem/year total effective dose equivalent (TEDE) as presented in
Section 6 of the LTP (SMUD 2006a). The DCGLs for surfaces were modified by SMUD to reflect
the ratio of radionuclide concentrations in the specific survey units (SU) that were being evaluated.
The applicable surface activity guidelines from the LTP and decommissioning technical basis
document (DTBD)-05-015 for the structural surfaces above the polar crane in the Reactor Building
Dome are as follows (SMUD 2006a and c):
Derived Concentration Guideline Levels (dpm/100 cm2)
Radionuclides Co-60a Cs-137a Gross Beta" EMCC
DCGL 40,200 182,000 43,000 593,400
aContainment Building Surface Single Nuclide DCGL for the
Renovation/Demolition Scenario as provided in Table 6-12 of the LTP.
bGross beta DCGL accounts for radionuclide fractions and hard to detects as
specified in the DTBD-05-015.
CDCGLEMC is the conservative value for the more restrictive Co-60 area factor of
13.8 as provided by SMUD.
All of the direct beta activity measurement results on the concrete structural surface walls (vertical
surfaces) were well within the DCGLs for Co-60 and Cs-137 as provided in the LTP (SMUD
2006a). The 25 direct measurement results (on the vertical concrete walls) were also within the gross
beta activity DCGL as determined by SMUD personnel using the LTP and technical basis
documents (SMUD 2006a, b and c). However, the six direct beta activity measurement locations on
the metal brackets that exceeded the gross beta activity DCGL were typically less than 500 cm2.
SMUD determined two area factors that were not independently verified by ORISE, one for Cs-137
which was 14.9 and one for Co-60 which was 13.8; ORISE used the lowest area factor in
determining the elevated measurement comparison (EMC) criteria for a 1 m2 area to be
conservative. This corresponds to a DCGLEMC of 593,400 dpm/100 cm2. All of the direct beta1695\Reports\2006-10-25 Confirmatory Survey Results
Rancho Seco Nuclear Generating Station
3
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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/m1/4/: accessed April 26, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.