ML17083A983

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Orau Independent Confirmatory Survey Summary, Results, and In-Process Inspection for the Interim On-Site Storage Building and Surrounding Area at the Rancho Seco Nuclear Generating Station
ML17083A983
Person / Time
Site: Rancho Seco
Issue date: 03/22/2017
From: Engel K, Jun Lee
Oak Ridge Institute for Science & Education
To: Cruz Z
Reactor Decommissioning Branch
Z. Cruz NMSS/DUWP/RDB 415-3808 T-8F07A
References
DCN 5293-SR-01-0, DE-SC0014664, NRC RFTA 16-012
Download: ML17083A983 (46)
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INDEPENDENT CONFIRMATORY SURVEY

SUMMARY

, RESULTS, AND IN-PROCESS INSPECTION FOR THE INTERIM ON-SITE STORAGE BUILDING AND SURROUNDING TWO-ACRE LICENSED SITE AREA AT THE RANCHO SECO NUCLEAR GENERATING STATION HERALD, CALIFORNIA K. M. Engel and J. D. Lee FINAL REPORT Prepared for the U.S. Nuclear Regulatory Commission March 2017 Further dissemination authorized to NRC only; other requests shall be approved by the originating facility or higher NRC programmatic authority.

ORAU provides innovative scientific and technical solutions to advance research and education, protect public health and the environment and strengthen national security. Through specialized teams of experts, unique laboratory capabilities and access to a consortium of more than 100 major Ph.D.-granting institutions, ORAU works with federal, state, local and commercial customers to advance national priorities and serve the public interest. A 501(c) (3) nonprofit corporation and federal contractor, ORAU manages the Oak Ridge Institute for Science and Education (ORISE) for the U.S. Department of Energy (DOE). Learn more about ORAU at www.orau.org.

NOTICES The opinions expressed herein do not necessarily reflect the opinions of the sponsoring institutions of Oak Ridge Associated Universities.

This report was prepared as an account of work sponsored by the United States Government.

Neither the United States Government nor the U.S. Department of Energy, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe on privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, mark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement or recommendation, or favor by the U.S. Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the U.S. Government or any agency thereof.

INDEPENDENT CONFIRMATORY SURVEY

SUMMARY

, RESULTS, AND IN-PROCESS INSPECTION FOR THE INTERIM ON-SITE STORAGE BUILDING AND SURROUNDING TWO-ACRE LICENSED SITE AREA AT RANCHO SECO NUCLEAR GENERATING STATION HERALD, CALIFORNIA Prepared by K. M. Engel and J. D. Lee ORAU MARCH 2017 FINAL REPORT Prepared for the U.S. Nuclear Regulatory Commission This document was prepared for the U.S. Nuclear Regulatory Commission (NRC) by the Oak Ridge Institute for Science and Education (ORISE) through an interagency agreement (NRC FIN no.

F-1244) between the NRC and the U.S. Department of Energy (DOE). ORISE is managed by Oak Ridge Associated Universities under DOE contract number DE-SC0014664.

Rancho Seco Confirmatory Survey Report 5293-SR-01-0

CONTENTS TABLES ........................................................................................................................................................... III FIGURES ........................................................................................................................................................ III ACRONYMS .................................................................................................................................................. IV EXECUTIVE

SUMMARY

.............................................................................................................................. 1

1. INTRODUCTION....................................................................................................................................... 2
2. SITE DESCRIPTION ................................................................................................................................. 2
3. OBJECTIVES................................................................................................................................................ 5
4. RADIONUCLIDES OF CONCERN ...................................................................................................... 6
5. PROCEDURES ............................................................................................................................................ 7 5.1 SURVEY UNIT SELECTION ................................................................................................................ 7 5.2 IN-PROCESS INSPECTION ................................................................................................................. 8 5.3 SURFACE SCANS ................................................................................................................................. 8 5.3.1 Confirmatory Survey Units...................................................................................................... 8 5.3.2 Land Area ................................................................................................................................... 8 5.4 SURFACE ACTIVITY MEASUREMENTS ............................................................................................. 8 5.4.1 Confirmatory Survey Units...................................................................................................... 9 5.4.2 Side-by-Side Areas .................................................................................................................... 9 5.5 SOIL SAMPLING .................................................................................................................................. 9 5.5.1 Soil Samples Collected by ORISE .......................................................................................... 9 5.5.2 Soil Samples Collected by Site................................................................................................. 9
6. SAMPLE ANALYSIS AND DATA INTERPRETATION ...............................................................10
7. FINDINGS AND RESULTS ...................................................................................................................10 7.1 OBSERVATIONS ................................................................................................................................10 7.2 SURFACE SCANS ...............................................................................................................................11 7.2.1 Confirmatory Survey Units....................................................................................................11 7.2.2 Land Area .................................................................................................................................12 7.3 SURFACE ACTIVITY MEASUREMENTS ...........................................................................................12 7.3.1 Confirmatory Survey Units....................................................................................................12 7.3.2 Side-by-Side Areas ..................................................................................................................12 7.4 RADIONUCLIDE CONCENTRATIONS IN SOIL...............................................................................14 7.4.1 Soil Samples Collected by ORISE ........................................................................................14 7.4.2 Soil Samples Collected by Site...............................................................................................14 Rancho Seco Confirmatory Survey Report i 5293-SR-01-0
8.

SUMMARY

AND CONCLUSIONS ......................................................................................................15

9. REFERENCES ...........................................................................................................................................17 APPENDIX A FIGURES APPENDIX B DATA TABLES APPENDIX C MAJOR INSTRUMENT APPENDIX D SURVEY AND ANALYTICAL PROCEDURES Rancho Seco Confirmatory Survey Report ii 5293-SR-01-0

FIGURES Figure 2.1. Rancho Seco Site Location ........................................................................................................... 3 Figure 2.2. Rancho Seco Property Map .......................................................................................................... 4 Figure 2.3. Map Indicating IOSB Location Within the Industrial Area .................................................... 5 TABLES Table 4.1. Rancho Seco Surface Soil DCGLs................................................................................................ 6 Table 4.2. Rancho Seco DCGL for Embedded Piping ................................................................................ 6 Table 4.3. Rancho Seco DCGL for Surfaces and Structures....................................................................... 6 Table 7.1. Scan Ranges for Confirmatory Units..........................................................................................11 Table 7.2. Summary of the Confirmatory Measurements ..........................................................................12 Table 7.3. Summary of the Side-by-Side Measurements ............................................................................13 Table 7.4. ORISE Soil Sample Number and Coordinates .........................................................................14 Table 7.5. Summary of Radionuclide Concentrations in ORISE Soil Samples ......................................14 Table 7.6. Summary of Radionuclide Concentrations in Site Collected Soil Samples ...........................15 Rancho Seco Confirmatory Survey Report iii 5293-SR-01-0

ACRONYMS CFR Code of Federal Regulations cm centimeter DAW dry active waste DCGL derived concentration guideline level dpm disintegrations per minute EPA U.S. Environmental Protection Agency FSS final status survey GPS global positioning system ha hectare IOSB Interim On-Site Storage Building ISFSI Independent spent fuel storage installation LTP license termination plan MDC minimum detectable concentration MWe megawatt electric power NaI sodium iodide NRC U.S. Nuclear Regulatory Commission ORISE Oak Ridge Institute for Science and Education ORAU Oak Ridge Associated Universities ROC radionuclide of concern RPD relative percent difference pCi/g picocuries per gram PSP project-specific plan RSNGS Rancho Seco Nuclear Generating Station RSS ranked set sampling SMUD Sacramento Municipal Utility District SOR sum-of-ratios SU survey unit TAPs total absorption peaks VSP visual sample plan Rancho Seco Confirmatory Survey Report iv 5293-SR-01-0

INDEPENDENT CONFIRMATORY SURVEY

SUMMARY

, RESULTS, AND IN-PROCESS INSPECTION OF THE INTERIM ON-SITE STORAGE BUILDING AND SURROUNDING TWO-ACRE LICENSED SITE AREA AT THE RANCHO SECO NUCLEAR GENERATING STATION HERALD, CALIFORNIA EXECUTIVE

SUMMARY

The U.S. Nuclear Regulatory Commission (NRC) requested the Oak Ridge Institute for Science and Education (ORISE) perform confirmatory surveys and in-process inspection activities at the Rancho Seco Nuclear Generating Station (RSNGS) in Herald, California. Confirmatory survey and in-process inspection activities are intended to ensure, if supported by the data, that RSNGS complies with the decommissioning commitments as prescribed in the approved license termination plan (LTP). The activities, performed August 29 - September 1, 2016, included gamma and beta scans in select areas of the Interim On-Site Storage Building (IOSB) and gamma scans of the surrounding land area, collection of random volumetric soil samples, independent total and removable activity measurements, as well as side-by-side direct measurements with the licensee. In addition, the licensee provided volumetric soil samples to ORISE for confirmatory analysis.

The data collected from the two confirmatory survey units within the IOSB did not indicate a presence of residual activity. Comparison of results generated by the side-by-side measurements do not appear to be statistically different. One discrete location was identified in the two-acre land area in need of further investigation and/or remediation. The location had already been identified and marked by the site. Soil samples collected by ORISE were in the range of typical background conditions. Soil samples collected by the licensee and analyzed by ORISE were in the typical range for background conditions, which is consistent with the licensees analysis of the soil samples.

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INDEPENDENT CONFIRMATORY SURVEY

SUMMARY

, RESULTS, AND IN-PROCESS INSPECTION OF THE INTERIM ON-SITE STORAGE BUILDING AND SURROUNDING TWO-ACRE LICENSED SITE AREA AT THE RANCHO SECO NUCLEAR GENERATING STATION HERALD, CALIFORNIA

1. INTRODUCTION Rancho Seco Nuclear Generating Station (RSNGS) was a 913-MWe pressurized water reactor designed by the Babcock and Wilcox Company. The 10 CFR Part 50 license (DPR-54) was issued in 1974, and the reactor attained initial criticality in September that same year. The facility began providing power commercially in April 1975. The Sacramento Municipal Utility District (SMUD) shut down Rancho Seco permanently in June 1989, after approximately 15 years of operation. In 1991, SMUD submitted the Rancho Seco Decommissioning Plan, which was approved by the U.S.

Nuclear Regulatory Commission (NRC) in 1995. SMUD began actively decommissioning Rancho Seco in February 1997 and completed transfer of all spent nuclear fuel in 2002. In 2009, after the completion of Phase 1 decommissioning, the only remaining portion of the site to be decommissioned was the Interim On-Site Storage Building (IOSB), which contained radiological waste from the Phase 1 decommissioning. Shipment of Phase 1 radiological waste from IOSB was completed in 2014. NRC was subsequently notified by SMUD that Phase II of decommissioning was ready to commence.

The NRC requested that Oak Ridge Institute for Science and Education (ORISE) conduct in-process inspections of RSNGS final status surveys (FSS) for the IOSB and confirmatory surveys of the surrounding two-acre licensed land area. At the time of the confirmatory survey, two IOSB survey units (SUs) had undergone FSS, and FSS was performed on two additional SUs during the site visit.

2. SITE DESCRIPTION The RSNGS site is located in the southeast part of Sacramento County, California. It lies either wholly or partly within sections 27, 28, 29, 32, 33, and 34 of Township 6 North, Range 8E. The site is approximately 42 kilometers (26 miles) north-northeast of Stockton and 40 kilometers southeast of Sacramento. Figure 2.1 depicts the location of the Rancho Seco site. The site is located between Rancho Seco Confirmatory Survey Report 2 5293-SR-01-0

the Sierra Nevada Mountains to the east and the Coast Range along the Pacific Ocean to the west in an area of flat to lightly rolling terrain at an elevation of approximately 200 feet above mean sea level. The area surrounding the site is almost exclusively agricultural and is used as grazing land and, more recently, for growing grapes. The climatology of the Rancho Seco site is typical of the Great Central Valley of California. The soils at Rancho Seco site can be categorized as hard to very hard silt and silty clays with dense to very dense sand and gravels.

Figure 2.1. Rancho Seco Site Location The owner-controlled site is approximately 1,004 hectares (2,480 acres). Within the owner-controlled area is an approximately 35-hectare (ha), fence-enclosed industrial area containing the nuclear facility. A 12-ha gas-fired power plant is located approximately 0.8 kilometers south of the Industrial Area boundary. Also, within the 1,004-hectare site are: the Rancho Seco Reservoir and Recreation Area, a solar powered electrical generating station, and an independent spent fuel storage installation (ISFSI) (SMUD 2014). Figure 2.2 provides a map of the site.

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Figure 2.2. Rancho Seco Property Map Figure 2.3 depicts the location of the IOSB within the industrial area. The IOSB was designed to store Phase 1 radiological waste in a retrievable mode. Storage was in two basic configurations, dependent on activity level. High activity waste was stored in a shielded, covered cell arrangement designed to accommodate a range of waste containers from 55-gallon drums to 300-cubic-foot disposable liners. The cells have individual shield covers, with cell cover and waste container handling accomplished by an overhead, remotely operated bridge crane system. The low activity radiological waste was stored in shielded open floor warehouse arrangement designed to accommodate a range of waste containers from 55-gallon drums to 120-cubic-foot metal bins (Rancho Seco 2014). The IOSB contains the following survey unit areas: dry active waste (DAW) bay, staging bay, staging bay floor, staging bay floor buffer, 15 storage cells, truck bay, hot cell, loading dock, loading dock buffer, cell deck, sump, embedded piping (hot cell drain), service head, septic tank, overhead crane, outside areas, roof, overhead piping, ventilation supply, and ventilation exhaust.

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Figure 2.3. Map Indicating IOSB Location Within the Industrial Area

3. OBJECTIVES The objectives of the confirmatory survey and in-process inspection activities were to provide independent contractor field data reviews and to generate independent radiological data for use by the NRC in evaluating the accuracy and adequacy of the licensees procedures and results.

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4. RADIONUCLIDES OF CONCERN The major radionuclides of concern (ROCs) for the IOSB and surrounding areas are beta-gamma emittersfission and activation productsresulting from reactor operation and the subsequent decommissioning. Of 26 potential radionuclides that could be present based on site operations, RSNGS only identified six within characterization samples; these were carbon-14 (C-14), cobalt-60 (Co-60), nickel-63 (Ni-63), strontium-90 (Sr-90), cesium-134 (Cs-134), and cesium-137 (Cs-137).

Cs-137 and Co-60 were identified during the characterization as the predominant radionuclides present on surfaces, in the soils, and in embedded piping (SMUD 2014). The applicable site-specific derived concentration guideline levels (DCGLs) for the ROCs are provided in Tables 4.1, 4.2, and 4.3.

Table 4.1. Rancho Seco Surface Soil DCGLs Radionuclide DCGL (pCi/g)a,b C-14 8.33E+06 Co-60 1.26E+01 Ni-63 1.52E+07 Sr-90 6.49E+03 Cs-134 2.24E+01 Cs-137 5.28E+01 aDCGLs from Rancho Seco License Termination Plan (SMUD 2014). Because of the relatively large DCGLs, neither background subtraction nor use of background reference areas are expected to be applied during the sites Final Status Survey (SMUD 2014).

bLimits apply to soil concentrations averaged over any 10,000 square meters (m2) to a depth of 15 centimeters (cm).

Surface soil DCGL values were applied as applicable to discrete pockets of subsurface soil contamination (SMUD 2014).

Table 4.2. Rancho Seco DCGL for Embedded Piping Radionuclide DCGL (dpm/100 cm2)a Gross beta 1.0E+05 aDCGLs from Rancho Seco License Termination Plan (SMUD 2014).

Table 4.3. Rancho Seco DCGL for Surfaces and Structures Radiation Type DCGL (dpm/100 cm2)

Gross beta 4.30E+04 aDCGLs from Rancho Seco License Termination Plan (SMUD 2014).

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Removable activity is assumed not to exceed 10% of the DCGL for surface and structures (i.e.,

4.3E+03 dpm/100 cm2). This assumption is based on Appendix 6-M, Parameters for Rancho Seco Structural Surfaces DCGL Derivation in Chapter 6 of the Rancho Seco Nuclear Generating Station License Termination Plan. (SMUD 2014).

Radionuclide area factors were applied as appropriate to the DCGLs based upon survey results to perform an elevated measurement comparison of any residual contamination that was identified in areas for confirmatory survey. Radionuclide area factors can be found in Chapter 6 of the Rancho Seco Nuclear Generating Station License Termination Plan (SMUD 2014).

5. PROCEDURES The confirmatory survey activities were conducted during the period of August 29 - September 1, 2016, in accordance with the project-specific confirmatory survey plan, the ORAU Radiological and Environmental Survey Procedure Manual and the ORAU Environmental Services and Radiation Training Quality Program Manual (ORAU 2016b and 2016c). The ORISE activities included independent scans and sampling of the land area; and scans, side-by-side measurements with the licensee, and observations of SMUD personnel conducting the FSSs for the IOSB.

5.1 SURVEY UNIT SELECTION Decisions relating to the selection of confirmatory survey units were based primarily on logistics, site survey schedule, and temporal boundaries. The effort to prepare a storage cell for entry is relatively extensive and proved to be the primary limitation. As a result, ORISE selected two cells that had already undergone FSS to perform confirmatory surveys. FSS had been performed in 3 survey units:

storage cells E-1, D-1, and C-1, while the remainder of the storage cells had not had an FSS performed at the time of the site visit. Cells E-1 and C-1 were selected for confirmatory survey. At the direction of NRC, two additional storage cells were identified for in-process inspection, including side-by-side measurements to be conducted during the SMUD FSS. Storage cells B-1 and A-1 were selected for these activities. In addition, side-by-side measurements were also collected in the staging bay, truck bay, and loading dock but were not part of the FSS process being conducted by SMUD at that time. In addition to storage cells, ORISE also performed gamma walk-over surveys and collected soil samples from the two-acre licensed land area that surrounds the IOSB.

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5.2 IN-PROCESS INSPECTION SMUD personnel were observed while conducting FSS in storage cells A-1 and B-1. Personnel were observed collecting direct surface activity measurements, swipe samples, and performing surface scans of walls and floors. SMUD surveyors used both handheld detectors and a floor monitor to conduct surveys. SMUD selected 15 random locations for the FSS using Visual Sample Plan (VSP).

Each of the 15 locations was marked with a 0.6 meters x 0.6 meters (0.36 m2) box drawn around the center point of each location. Scanning was conducted on 100% of the surface area within each 0.36 m2 box. One-minute surface activity measurements were taken at the center of each box.

5.3 CONFIRMATORY SURFACE SCANS Gamma scans were performed using Ludlum Model 44-10, 2-inch by 2-inch sodium iodide (2x2 NaI) detectors. In addition, gamma detectors were coupled to the global positioning system (GPS) data logging system to enable real-time gamma count rate and position data capture for the land area survey. Beta scans were performed using Ludlum Model 43-68 gas proportional detectors. All detectors were coupled to Ludlum Model 2221 ratemeter-scalers with audible indicators.

5.3.1 Confirmatory Survey Units Low to medium density alpha-plus-beta and high density gamma radiation scans were performed on accessible lower surfaces (floors, lower walls, trenches) inside storage cells C-1 and E-1 in the IOSB as part of the confirmatory survey. A gamma scan was performed of the embedded piping as far as was accessible. The embedded piping was not accessible for beta scans.

5.3.2 Land Area Low to medium density gamma radiation scans were performed on the surrounding two-acre land area. The land area consisted of asphalt immediately surrounding the building followed by a steep berm. Accessibility of the berm was limited due its steep incline and unstable footing.

5.4 SURFACE ACTIVITY MEASUREMENTS All direct beta measurements were performed using the Ludlum Model 43-68 gas proportional detectors coupled to Ludlum Model 2221 ratemeter-scalers.

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5.4.1 Confirmatory Survey Units For confirmatory surveys, six locations were randomly chosen in each storage cell, C-1 and E-1, for direct beta measurements and smears. Measurement locations were on the floor and lower walls in the two confirmatory survey units. Direct measurements were unable to be performed in the embedded piping. No judgmental locations were selected based upon surface scan results.

5.4.2 Side-by-Side Areas Side-by-side surface activity measurements were performed with SMUD in storage cells A-1 and B-1, the staging bay, truck bay, and loading dock. In the storage cells, the locations were chosen by SMUD personnel and corresponded to FSS survey locations. In the staging bay, truck bay, and loading dock, the locations were chosen based on elevated scan data collected by ORISE. These areas had not yet undergone FSS. A total of 30 random and 10 judgmental side-by-side direct beta measurements were collected. Smear samples were collected at all direct measurement locations within the IOSB to determine the fraction of removable activity, except for six locations in storage cell B-1 due to logistical limitations.

5.5 SOIL SAMPLING 5.5.1 Confirmatory Soil Samples Surface soil samples (0-15 cm in depth) were collected from six random locations within the land area. Locations were randomly selected using a ranked set sampling (RSS) approach. As described in the project-specific plan (PSP), the RSS process, following U.S. Environmental Protection Agency (EPA) guidance, was used to generate the random locations from which the soil samples were collected (EPA 2002). One-minute static gamma measurements were collected from 18 randomly selected locations using the 2x2 NaI detector. After ranking those 18 measurements, 6 soil samples were collected for laboratory analyses.

5.5.2 Confirmatory Analysis of SMUD FSS Soil Samples Following the site visit, SMUD sent ten FSS soil samples to ORISE for confirmatory analysis. The samples were collected by site personnel prior to ORISEs site visit; however, the SMUD results were not finalized at the time of the site visit. The samples were shipped under chain of custody and received by ORISE on September 9, 2016.

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6. SAMPLE ANALYSIS AND DATA INTERPRETATION Samples and data collected at the site were returned to the ORISE facility in Oak Ridge, Tennessee for analysis and interpretation. Sample custody was transferred to Radiological and Environmental Analytical Laboratory. Sample analyses were performed in accordance with the ORAU Radiological and Environmental Analytical Laboratory Procedures Manual (ORAU 2016d). Soil samples were analyzed by gamma spectroscopy and the results reported in picocuries per gram (pCi/g). The radionuclides of interest were Co-60 and Cs-137; however, spectra were also reviewed for other gamma-emitting fission and activation products associated with the RSNGS.

Direct measurement data were converted to units of disintegration per minute per 100 square centimeters (dpm/100 cm2). Surface activity levels were calculated from the gross, rather than net counts, as SMUD has elected to not correct for background contribution toward the gross beta activity DCGL.

Gross surface activity and surface soil concentrations were compared with the DCGLs presented in Section 4 of this report. Removable activity was compared with 10% of the total surface activity DCGL. ORISEs and SMUDs contractor laboratory results for soil samples collected by the site were compared to one another and to the DCGLs.

7. FINDINGS AND RESULTS The results of the confirmatory survey are discussed in the subsections below.

7.1 OBSERVATIONS SMUD staff were observed collecting FSS data in storage cells A-1 and B-1. Personnel marked locations for data collection, performed direct measurements, collected smear samples, and conducted surface scanning. SMUD personnel used a Ludlum Model 44-116 plastic scintillator for beta detection coupled to a Ludlum Model 2350-1 data logger. The ORISE observations are discussed below.

Overall, scan speeds were appropriate and at correct distance from surfaces. SMUD has, however, reduced the interaction between the surveyor and the analysis of data in the field. Rather than technicians listening to the audio output, the ratemeters are programmed to alarm at predetermined Rancho Seco Confirmatory Survey Report 10 5293-SR-01-0

set points (10% of the DCGL) and record the scan data, which are analyzed after the survey is completed. Per SMUDs approach, this removes the need for the surveyor to observe the audible output.

Generally for final status surveys, surface scans are performed first in a survey unit to identify any areas of elevated direct radiation requiring investigation and are followed by the judgmental and/or random direct measurements or smears. SMUDs approach is to scan the measurement location box after the direct measurement and smear have been collected in the center of the measurement location box. In this situation, this approach is acceptable due to the high DCGL, low alarm set point, and scan data reviewed after the survey is completed to identify areas of elevated radiation.

One procedure implementation issue was identified that required further evaluation. It was identified that SMUD personnel were collecting smear samples prior to direct measurements, and some were noted as covering less than 100 cm2. In addition, smear samples were being collected from points other than where direct measurements were taken (but still within the 0.36 m2 measurement location box). The observations regarding smear sampling were relayed to both NRC and site personnel, and the issues were formally addressed during the following days pre-job briefing. While still on-site, ORISE was able to observe that the issues had been adequately addressed.

7.2 SURFACE SCANS 7.2.1 Confirmatory Survey Units Most confirmatory gamma and beta scan results in storage cells C-1 and E-1 exhibited radiation levels consistent with detector background ranges. Table 7.1 provides a scan range summary for each confirmatory unit.

Table 7.1. Scan Ranges for Confirmatory Units Gamma Scan Ranges (cpm) Beta Scan Ranges (cpm)

Confirmatory Unit C-1 9,000 to 12,000 250 to 400 E-1 9,000 to 12,000 300 to 600 Rancho Seco Confirmatory Survey Report 11 5293-SR-01-0

7.2.2 Land Area The majority of the gamma scan results of the land area exhibited radiation levels within the detector background range of 6,000 to 8,000 cpm for the soil and 6,900 to 9,400 cpm for the asphalt. One location of elevated direct gamma radiation of 45,000 cpm was identified adjacent to the south, exterior wall of the IOSB. This location had already been identified by the site and scheduled for remediation. At the time of the site visit, the land area had not undergone FSS. Figure A-1 is a map with scan data for the surveyed land area.

7.3 SURFACE ACTIVITY MEASUREMENTS 7.3.1 Confirmatory Survey Units Table 7.2 provides a summary of the confirmatory measurements.

Table 7.2. Summary of the Confirmatory Measurements Removable Activity (dpm/100 cm²) Gross Surface Activity (dpm/100 cm²)

C-1 -1 to 5 1,500 to 2,300 E-1 -2 to 4 1,600 to 2,300 All confirmatory measurements for gross surface activity were below the DCGL of 43,000 cpm/100 cm2. All confirmatory measurements for removable activity were below 10% of the DCGL for gross removable activity. Table B.1 provides the full results of the confirmatory survey measurements.

Figures A-2 and A-3 show the confirmatory survey locations in the storage cells.

7.3.2 Side-by-Side Areas It is important to note that SMUD calculated gross surface activities values using a surface efficiency (Es) of 0.296. The empirically determined Es value of 0.296 was derived by SMUD utilizing methodology presented in the approved LTP, Chapter 5. This approach is conservative in nature taking into account such things as self-attenuation, back scatter, and attenuation by certain coatings.

For the purpose of direct data comparison, ORISE results assume the empirically determined Es of 0.296 in surface activity calculations.

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The ORISE direct measurements were directly compared to SMUDs direct measurements through calculation of the relative percent difference (RPD), a measure of precision which is defined in DOE/EM-0089T, Rev. 2 DOE Methods for Evaluating Environmental and Waste Management Samples (DOE 1994). ORISE used a modified version of the RPD equation by removing the absolute value from the numerator, as shown:

= x 100

( + )

( 2 )

Where:

P = SMUD measurement result S = ORISE measurement result The reason for removing the absolute value is to allow the direction of the difference to be evaluated for the presence of a systematic bias.

Table 7.3 provides a summary of the side-by-side measurements.

Table 7.3. Summary of the Side-by-Side Measurements Removable Activity (dpm/100 cm²) Gross Surface Activity (dpm/100 cm²)

ORISE -2 to 26 1,500 to 100,000 SMUD -- 1,600 to 120,000 RPD -- -22.7 to 37.4 In all, 88% of the 40 comparative measurements resulted in an RPD of less than 25%. The mean of ORISEs and SMUDs measurements were compared, and the RPD for the means was 17%. These data indicate ORISE and SMUD are not statistically different from one another. Based on the data presented in Table B-2, no further statistical testing was deemed necessary.

Only one direct measurement collected during the side-by-side measurements exceeded the DCGL of 43,000 dpm/100 cm2 for both ORISE and SMUD; however, this measurement was in the truck bay, which had not had the FFS performed as of the date of the site visit. All smears collected by ORISE during the side-by-side measurements were below 10% of the DCGL for gross surface activity. Full results of the side-by-side measurements are presented in Table B-2.

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7.4 RADIONUCLIDE CONCENTRATIONS IN SOIL 7.4.1 Confirmatory Soil Samples Soil samples were collected based on the results of the gamma walkover survey. Table 7.4 presents a summary of the confirmatory soil sampling. Figure A-4 provides a site map indicating the soil sample locations.

Table 7.4. ORISE Soil Sample Number and Coordinates Coordinates (feet) Direct Gamma Location ID Depth (cm)

Northing Easting Measurement (cpm) 5293M0001 1889205 6812977 15 7,500 5293M0002 1889235 6812758 15 7,900 5293M0003 1889225 6812852 15 7,800 5293M0004 1889198 6812825 15 7,700 5293M0005 1889218 6812945 15 7,500 5293M0006 1889238 6812887 15 7,700 A summary of the analytical results for the land area samples collected by ORISE are presented in Table 7.5.

Table 7.5. Summary of Radionuclide Concentrations in ORISE Soil Samples Co-60 (pCi/g) Cs-137 (pCi/g) SOR

-0.009 to 0.024 0.019 to 0.056 0.000 to 0.002 The DCGL for surface soils is 52.8 pCi/g and 12.6 pCi/g for Cs-137 and Co-60, respectively. All concentrations are below their respective DCGL, and sum-of-ratio (SOR) for all samples is less than 0.002. Full results for the confirmatory soil sample concentrations are presented in Table B.3.

7.4.2 Confirmatory Analysis of SMUD FSS Soil Samples At the request of NRC, ORISE conducted the analysis of ten soil samples collected by SMUD. The analytical data from both ORISE and SMUD indicate that Co-60 and Cs-137 concentrations are Rancho Seco Confirmatory Survey Report 14 5293-SR-01-0

representative of site background and very near their respective minimum detectable concentration (MDC).

The analytical results for confirmatory samples and results comparisons are provided in Table B.4.

Most all concentrations were less than the analytical MDC. Therefore, a statistical comparison of the individual results would not provide meaningful information. In this particular case, the datasets have been evaluated as a whole and determined to be comparable. Table 7.6 provides comparative summary statistics of split sample results generated by ORISE and SMUD.

Table 7.6. Summary of Radionuclide Concentrations in Site Collected Soil Samples Co-60 pCi/g Cs-137 pCi/g Min Max Mean Min Max Mean ORISE 0.000 0.026 0.009 0.004 0.036 0.016 SMUD -0.013 0.049 0.020 -0.005 0.036 0.011

8.

SUMMARY

AND CONCLUSIONS At the NRCs request, ORISE conducted confirmatory survey activities within the IOSB and surrounding two-acre land area, as well as an in-process inspection of the sites FSS data collection during the period of August 29 - September 1, 2016. The survey activities included beta and gamma radiation surface scans, direct and removable confirmatory measurements, side-by-side direct measurements, and soil sampling.

ORISE reviewed the Rancho Seco Nuclear Generating Station License Termination Plan, revision 2 in preparation of the site visit and found it to be adequate. ORISE also observed the implementation of the sites FSS during the site visit. Overall, SMUD personnel implemented the FSS appropriately with a few minor discrepancies, mainly in the collection of smear samples. SMUD personnel collected smear samples prior to the direct measurement, samples were less than 100 cm2, and samples were collected from areas other than where the direct measurement was collected. These issues were relayed to the site and corrected upon the next observed survey.

Gamma surface scans of the land area exhibited detector response indistinguishable from background except in one discrete location on the south side of the IOSB in the asphalt area.

Gamma response at this location was approximately 45,000 cpm compared to a background of Rancho Seco Confirmatory Survey Report 15 5293-SR-01-0

approximately 8,000 cpm for asphalt surfaces. The site is aware of this location as it is had been marked for further investigation and/or remediation prior to the ORISE survey.

The majority of the confirmatory beta and gamma surface scans conducted in Cells C-1 and E-1 were indistinguishable from background, with no instances of elevated surface activity identified.

Direct measurement results collected in Cells C-1 and E-1 were also determined to be within the range of background and a fraction of the sites gross beta surface activity DCGL. Smears collected from direct measurement locations exhibited little to no removable activity.

Side-by-side measurements collected between ORISE and the site were in agreement with 88% of the measurements having an RPD of less than 25%. The mean of the two data sets had an RPD of 16.7%, indicating the data are not statistically different from one another. Of the 40 measurements collected for side-by-side comparison, only one measurement exceeded the gross surface activity DCGL of 43,000 dpm/100 cm2 (removable activity was less than 10% of this DCGL). However, this area had not undergone an FSS at the time of the site visit.

The Co-60 and Cs-137 concentrations in the six random confirmatory soil samples were well below the DCGLs with all Co-60 results less than the respective analytical MDC and detectable Cs-137 concentrations were in range of typical background conditions.

Ten samples that were collected by the site were sent to ORISE for analysis and data comparison.

ORISE analysis indicated all ten samples to have concentrations of Co-60 less than their respective MDC. Two of the ten samples exhibited detectable amounts of Cs-137 but were still in the range of site background conditions. The SMUD analytical data shows all ten samples below their respective MDC for both Co-60 and Cs-137. Based on these results the two datasets are considered adequately comparable.

Rancho Seco Confirmatory Survey Report 16 5293-SR-01-0

9. REFERENCES DOE 1994. DOE Methods for Evaluating Environmental and Waste Management Samples, Rev. 2. U.S.

Department of Energy. Washington D.C. October.

EPA 2002. Guidance on Choosing a Sampling Design for Environmental Data Collection. (EPA QA/G-5S). December.

NRC 1997. Minimum Detectable Concentrations with Typical Radiation Survey Instruments for Various Contaminants and Field Conditions. NUREG-1507. U.S. Nuclear Regulatory Commission. Washington, D.C. December.

ORAU 2014. ORAU Radiation Protection Manual. Oak Ridge, Tennessee. October.

ORAU 2016a. ORAU Health and Safety Manual. Oak Ridge, Tennessee. January ORAU 2016b. ORAU Radiological and Environmental Survey Procedures Manual. Oak Ridge, Tennessee.

November 10.

ORAU 2016c. ORAU Environmental Services and Radiation Training Quality Program Manual. Oak Ridge, Tennessee. November 9.

ORAU 2016d. ORAU Radiological and Environmental Analytical Laboratory Procedures Manual. Oak Ridge, Tennessee. November 9.

Rancho Seco 2014. Rancho Seco Site Scoping Survey. Survey Package Number: SA83072BS. Sacramento Municipal Utility District. Herald, California. October.

SMUD 2014. Rancho Seco Nuclear Generating Station License Termination Plan. Revision 2. Sacramento Municipal Utility District. Herald, California. October.

Rancho Seco Confirmatory Survey Report 17 5293-SR-01-0

APPENDIX A FIGURES Rancho Seco Confirmatory Survey Report 5293-SR-01-0

Figure A-1. Gamma Walkover Survey of the Land Area Surrouding the IOSB Rancho Seco Confirmatory Survey Report A-1 5293-SR-01-0

Figure A-2. Confirmatory Survey Locations - Storage Cell C-1 Rancho Seco Confirmatory Survey Report A-2 5293-SR-01-0

Figure A-3. Confirmatory Survey Locations - Storage Cell E-1 Rancho Seco Confirmatory Survey Report A-3 5293-SR-01-0

Figure A-4. ORISE Soil Sample Locations Rancho Seco Confirmatory Survey Report A-4 5293-SR-01-0

APPENDIX B DATA TABLES Rancho Seco Confirmatory Survey Report 5293-SR-01-0

Table B.1. Confirmatory Survey Results Removable Gross Surface Coordinates (meters)a Activity Activity Location ID Area Surface (dpm/100 cm²) (dpm/100 cm²)

X Y Beta Beta 5293R0001/R 4.6 0.5 C-1 S. Wall 5 1,700 5293R0002/R 0.5 3.5 C-1 Floor 4 2,300 5293R0003/R 3.2 1.5 C-1 W. Wall 5 1,700 5293R0004/R 1.8 0.1 C-1 Floor 2 1,800 5293R0005/R 4.3 1.8 C-1 Floor 2 1,700 5293R0006/R 1.2 1.0 C-1 N. Wall -1 1,500 Mean 3 1,800 5293R0041/R 0.8 2.1 E-1 Floor 4 2,100 5293R0042/R 4.2 3.9 E-1 Floor -1 2,300 5293R0043/R 1.1 0.3 E-1 N. Wall 0 1,600 5293R0044/R 3.6 0.8 E-1 S. Wall 4 1,800 5293R0045/R 2.5 1.3 E-1 E. Wall -2 1,900 5293R0046/R 4.8 1.5 E-1 Floor 0 1,900 Mean 1 2,000 a Locations measured from the southwest corner of the floor or lower left corner of wall.

Rancho Seco Confirmatory Survey Report B-1 5293-SR-01-0

Table B.2. Side by Side Measurements Results and Comparison ORISE SMUD Coordinates SMUD Removable Gross Surface Gross Surface Location ID (meters)a Location Area Surface Activity Activity Activity IDb (dpm/100 cm²) (dpm/100 cm²) (dpm/100 cm²) RPD X Y Beta Beta Beta 5293R0026/R -- -- F7 A-1 Wall -1 1,700 2,000 13.3 5293R0027/R -- -- F4 A-1 Wall 4 1,500 2,000 27.7 5293R0028/R -- -- F13 A-1 Wall 4 1,800 2,100 18.4 5293R0029/R -- -- F1 A-1 Wall 3 1,800 1,800 -1.7 5293R0030/R -- -- F10 A-1 Wall 2 1,600 2,000 17.9 5293R0031/R -- -- F6 A-1 Wall 2 1,900 1,900 1.1 5293R0032/R -- -- F15 A-1 Wall 3 1,700 2,000 15.7 5293R0033/R -- -- F12 A-1 Wall 0 1,800 1,900 6.6 5293R0034/R -- -- F9 A-1 Wall 3 1,600 1,600 -1.1 5293R0035/R -- -- F5 A-1 Wall 0 2,100 1,700 -22.7 5293R0036/R -- -- F2 A-1 Wall 4 1,800 1,800 -1.4 5293R0037/R -- -- F14 A-1 Wall 0 1,800 1,900 5.0 5293R0038/R -- -- F11 A-1 Wall 0 1,900 2,100 7.9 5293R0039/R -- -- F3 A-1 Floor 2 2,000 2,200 7.1 5293R0040/R -- -- F8 A-1 Wall -1 1,600 1,900 15.6 5293R0007/R -- -- F9 B-1 Wall 3 1,600 1,800 9.5 5293R0008/R -- -- F12 B-1 Wall -2 1,700 1,700 0.5 5293R0009/R -- -- F6 B-1 Wall 3 1,800 1,900 8.2 5293R0010/R -- -- F11 B-1 Wall 0 1,800 2,000 10.9 5293R0011/R -- -- F2 B-1 Wall 3 1,700 1,900 12.2 5293R0012/R -- -- F8 B-1 Wall 3 1,800 2,000 12.3 5293R0013/R -- -- F5 B-1 Wall 4 1,900 1,800 -3.4 5293R0014/R -- -- F14 B-1 Wall 0 1,700 1,900 12.2 Rancho Seco Confirmatory Survey Report B-2 5293-SR-01-0

Table B.2. Side by Side Measurements Results and Comparison ORISE SMUD Coordinates SMUD Removable Gross Surface Gross Surface Location ID (meters)a Location Area Surface Activity Activity Activity IDb (dpm/100 cm²) (dpm/100 cm²) (dpm/100 cm²) RPD X Y Beta Beta Beta 5293R0015/R -- -- F10 B-1 Wall 2 1,700 1,700 -3.5

-- -- -- F13 B-1 Wall -- 1,800 2,000 14.0

-- -- -- F7 B-1 Wall -- 1,500 2,000 27.9

-- -- -- F15 B-1 Floor -- 2,000 2,200 8.3

-- -- -- F3 B-1 Floor -- 1,900 2,000 5.7

-- -- -- F4 B-1 Wall -- 1,900 2,000 1.3

-- -- -- F1 B-1 Wall -- 1,600 1,800 15.2 5293R0016/J 4.4 7.9 -- Staging Bay Floor 0 24,000 32,000 25.7 5293R0017/J 12.4 4.0 -- Staging Bay Floor 8 12,000 13,000 8.0 5293R0018/J 13.4 2.3 -- Staging Bay Floor 9 13,000 14,000 5.7 5293R0019/J 8.0 10.5 -- Staging Bay Floor 2 4,200 5,600 28.9 5293R0020/J 8.0 10.5 -- Staging Bay Floor 4 4,400 5,200 16.7 5293R0021/J 5.6 7.5 -- Truck Bay Floor 26 100,000 120,000 19.3 5293R0022/J 6.6 6.6 -- Loading Dock Floor 2 1,800 1,700 -3.5 5293R0023/J 7.7 10.6 -- Truck Bay Floor -2 2,700 3,100 14.6 5293R0024/J 15.9 11.7 -- Truck Bay Floor 2 2,200 2,200 0.1 5293R0025/J 5.3 7.5 -- Truck Bay Floor 5 12,000 17,000 37.4 Mean 3 5,800 6,900 17.0 a Locations measured from the southwest corner of the floor or lower left corner of the wall b Smear samples were not collected at SMUD ID Locations F13, F7, F15, F3, F4, and F1 in storage cell B-1 due to logistical limitations.

Rancho Seco Confirmatory Survey Report B-3 5293-SR-01-0

Table B.3. Radionuclide Concentrations in ORISE Soil Samples Co-60 (pCi/g) Cs-137 (pCi/g)

Location ID a b SOR Conc. TPU MDC Conc. TPU MDC 5293M0001/R 0.000 +/- 0.025 0.053 0.031 +/- 0.015 0.029 0.001 5293M0002/R -0.009 +/- 0.014 0.038 0.021 +/- 0.012 0.026 0.000 5293M0003/R 0.009 +/- 0.018 0.043 0.029 +/- 0.014 0.027 0.001 5293M0004/R 0.024 +/- 0.021 0.051 0.019 +/- 0.015 0.034 0.002 5293M0005/R -0.009 +/- 0.014 0.051 0.056 +/- 0.021 0.038 0.000 5293M0006/R -0.004 +/- 0.018 0.036 0.033 +/- 0.013 0.024 0.000 a Uncertainties represent the 95% confidence level, based on total propagated uncertainties.

b MDC = minimum detectable concentration Table B.4. Analytical Laboratory Comparison of Radionuclide Concentrations in Soil Samples ORISE ORISE pCi/g SMUD pCi/g ORISE SMUD Analyte Result Uncert.a MDCb Result Uncert. MDC Sample ID Sample ID Co-60 0.018 0.022 0.054 0.049 0.049 0.106 11727S0007 2016-0019 Cs-137 0.036 0.015 0.029 0.036 0.054 0.096 Co-60 0.001 0.018 0.035 0.030 0.028 0.062 11727S0008 2016-0020 Cs-137 0.010 0.011 0.026 0.023 0.032 0.062 Co-60 0.010 0.014 0.033 0.049 0.031 0.074 11727S0009 2016-0021 Cs-137 0.014 0.016 0.039 -0.005 0.035 0.064 Co-60 0.008 0.016 0.036 -0.013 0.031 0.050 11727S0010 2016-0022 Cs-137 0.019 0.011 0.023 0.000 0.063 0.052 Co-60 0.026 0.019 0.052 0.010 0.027 0.049 11727S0011 2016-0023 Cs-137 0.004 0.022 0.047 0.012 0.034 0.063 Rancho Seco Confirmatory Survey Report B-4 5293-SR-01-0

Table B.4. Analytical Laboratory Comparison of Radionuclide Concentrations in Soil Samples ORISE ORISE pCi/g SMUD pCi/g ORISE SMUD Analyte Result Uncert.a MDCb Result Uncert. MDC Sample ID Sample ID Co-60 0.001 0.018 0.037 0.007 0.025 0.049 11727S0012 2016-0024 Cs-137 0.023 0.010 0.020 0.034 0.029 0.053 Co-60 0.010 0.022 0.051 0.031 0.034 0.070 11727S0013 2016-0025 Cs-137 0.005 0.022 0.048 0.004 0.031 0.056 Co-60 0.002 0.018 0.036 0.002 0.028 0.054 11727S0014 2016-0026 Cs-137 0.023 0.011 0.024 0.0 0.060 0.050 Co-60 0.015 0.018 0.043 0.026 0.032 0.060 11727S0015 2016-0027 Cs-137 0.006 0.018 0.042 0.00002 0.030 0.056 Co-60 0.000 0.018 0.039 0.010 0.023 0.044 11727S0016 2016-0028 Cs-137 0.020 0.012 0.025 0.001 0.027 0.048 a Uncertainties represent the 95% confidence level, based on total propagated uncertainties.

b MDC = minimum detectable concentration Rancho Seco Confirmatory Survey Report B-5 5293-SR-01-0

APPENDIX C MAJOR INSTRUMENTATION Rancho Seco Confirmatory Survey Report 5293-SR-01-0

The display of a specific product is not to be construed as an endorsement of the product or its manufacturer by the author or her employer.

C.1 SCANNING AND MEASUREMENT INSTRUMENT/DETECTOR COMBINATIONS C.1.1 GAMMA Ludlum NaI Scintillation Detector Model 44-10, Crystal: 5.1 cm x 5.1 cm (Ludlum Measurements, Inc., Sweetwater, Texas) coupled to:

Ludlum Ratemeter-scaler Model 2221 (Ludlum Measurements, Inc., Sweetwater, Texas) coupled to:

Trimble Data Logger (Trimble Navigation Limited, Sunnyvale, CA)

C.1.2 ALPHA-PLUS-BETA Ludlum Gas-flow Proportional Detector Model 43-68, 126 cm2 physical area, 0.8 mg/cm2 mylar window, coupled to:

Ludlum Ratemeter-scaler Model 2221 (Ludlum Measurements, Inc., Sweetwater, TX)

C.2 LABORATORY ANALYTICAL INSTRUMENTATION Low Background Gas Proportional Counter Model LB-5100-W (Tennelec/Canberra, Meriden Connecticut)

High-Purity, Extended Range Intrinsic Detector CANBERRA/Tennelec Model No: ERVDS30-25195 (Canberra, Meriden, Connecticut)

Used in conjunction with:

Lead Shield Model G-11 (Nuclear Lead, Oak Ridge, Tennessee) and Multichannel Analyzer Canberras Gamma Software Dell Workstation (Canberra, Meriden, Connecticut)

High-Purity, Intrinsic Detector EG&G ORTEC Model No. GMX-45200-5 Used in conjunction with:

Lead Shield Model G-11 Lead Shield Model SPG-16-K8 (Nuclear Data)

Multichannel Analyzer Canberras Gamma Software Rancho Seco Confirmatory Survey Report C-1 5293-SR-01-0

Dell Workstation (Canberra, Meriden, Connecticut)

High-Purity, Intrinsic Detector EG&G ORTEC Model No. GMX-30P4 Used in conjunction with:

Lead Shield Model G-11 Lead Shield Model SPG-16-K8 (Nuclear Data)

Multichannel Analyzer Canberras Gamma Software Dell Workstation (Canberra, Meriden, Connecticut)

High-Purity, Intrinsic Detector EG&G ORTEC Model No. CDG-SV-76/GEM-MX5970-S Used in conjunction with:

Lead Shield Model G-11 Lead Shield Model SPG-16-K8 (Nuclear Data)

Multichannel Analyzer Canberras Gamma Software Dell Workstation (Canberra, Meriden, Connecticut)

Rancho Seco Confirmatory Survey Report C-2 5293-SR-01-0

APPENDIX D SURVEY AND ANALYTICAL PROCEDURES Rancho Seco Confirmatory Survey Report 5293-SR-01-0

D.1 PROJECT HEALTH AND SAFETY ORISE performed all survey activities in accordance with the ORAU Radiation Protection Manual, the ORAU Health and Safety Manual, and the ORAU Radiological and Environmental Survey Procedures Manual (ORAU 2014, ORAU 2016a, and ORAU 2016b). Prior to on-site activities, a work-specific hazard checklist was completed for the project and discussed with field personnel. The planned activities were thoroughly discussed with site personnel prior to implementation to identify hazards present.

Additionally, prior to performing work, a pre-job briefing and walk down of the area were completed with field personnel to identify hazards present and discuss safety concerns. Should ORISE have identified a hazard not covered in the ORAU Radiological and Environmental Survey Procedures Manual or the projects work-specific hazard checklist for the planned survey and sampling procedures, work would not have been initiated or continued until it was addressed by an appropriate job hazard analysis and hazard controls.

D.2 CALIBRATION AND QUALITY ASSURANCE Calibration of all field instrumentation was based on standards/sources, traceable to National Institute of Standards and Technology (NIST).

Field survey activities were conducted in accordance with procedures from the following ORAU documents:

  • ORAU Environmental Services and Radiation Training Quality Program Manual (ORAU 2016c)
  • ORAU Radiological and Environmental Analytical Laboratory Procedures Manual (ORAU 2016d)
  • ORAU Radiological and Environmental Survey Procedures Manual (ORAU 2016b)

Quality control procedures include:

  • Daily instrument background and check-source measurements to confirm that equipment operation is within acceptable statistical fluctuations
  • Participation in Mixed-Analyte Performance Evaluation Program, NIST Radiochemistry Intercomparison Testing Program, and Intercomparison Testing Program Laboratory Quality Assurance Programs Rancho Seco Confirmatory Survey Report D-1 5293-SR-01-0
  • Training and certification of all individuals performing procedures
  • Periodic internal and external audits D.3 SURVEY PROCEDURES D.

3.1 BACKGROUND

MEASUREMENTS Background measurements were not collected as SMUD has elected to not correct for background contribution in the gross beta activity DCGL.

D.3.2 SURFACE SCANS Scans for elevated gamma radiation were performed by passing the detector slowly over the surface.

The distance between the detector and surface was maintained at a minimum. NUREG-1507, Table 6.4, provides NaI Scintillation Detector Scan MDCs for Common Radiological Contaminants. For Cs-137, the scan minimum detectable concentration (MDC) for the 2x2 NaI is 6.4 picocuries per gram (pCi/g). The NaI detectors were used solely as a qualitative means to identify elevated radiation levels in excess of background. Identifications of elevated radiation levels that could exceed the site criteria were determined based on an increase in the audible signal from the indicating instrument.

Surface scan MDCs for the detectors were estimated using the approach described in NUREG-1507 (NRC 1997). The scan MDC is a function of many variables, including a two-second observation interval, a specified level of performance at the first scanning stage of 90% true positive and 15%

false positive rate, which yields a d' value of 2.32 (NUREG-1507, Table 6.1), and a surveyor efficiency of 0.5. The total weighted efficiency for beta was 0.14, based on a relative fraction of 84%

for Cs-137 and a surface efficiency of 0.296. The scan MDC was calculated using the following equation:

x x (/60) x (60/)

=

x x 100 2 Rancho Seco Confirmatory Survey Report D-2 5293-SR-01-0

Where:

d' = index of sensitivity Cb = background (cpm) i = observation interval (sec) p = surveyor efficiency t = total efficiency The scan MDC for a nominal instrument background of 280 cpm was 1,700 dpm/100 cm2 for the Model 43-68.

D.3.2 SURFACE ACTIVITY MEASUREMENTS Measurements of gross beta surface activity levels were performed using hand-held gas proportional detectors coupled to portable ratemeter-scalers. Count rates (cpm), which were a one-minute count with the detector held in a static position, were converted to activity levels (dpm/100 cm2) by dividing the count rate by the total static efficiency (i x s) and correcting for the physical area of the detector plus background. The total weighted efficiency of 0.14, based on a relative fraction of 84%

for Cs-137 and a surface efficiency of 0.296, was used for surface activity calculations. The MDC for static survey activity measurements was calculated using the following equation:

3 + (4.65)

=

Where:

B = background in time interval, T T = count time (min) used for field instruments tot = total efficiency = x G = geometry correction factor = 1.26 (for the Model 43-68)

The static MDC was 460 dpm/100 cm2, based on a nominal instrument background of 280 cpm.

D. 3.3 REMOVABLE ACTIVITY SAMPLING Smear samples for removable gross alpha and gross beta contamination were obtained from independent confirmatory measurement locations as well as the side-by-side measurement locations.

Removable activity samples were collected using numbered filter paper disks. Moderate pressure was Rancho Seco Confirmatory Survey Report D-3 5293-SR-01-0

applied to the smear and approximately 100 cm2 of the surface was wiped. Smears for gross beta analysis were placed in labeled envelopes. Locations and other pertinent data were recorded. All samples were transferred under chain-of-custody to the ORISE Radiological and Environmental Analytical Laboratory.

D.3.4 SOIL SAMPLING Soil samples (approximately 0.5 kilograms each) were collected using a clean garden trowel and then transferred into a new sample container by ORISE personnel. ORISE personnel labeled each sample in accordance with ORAU survey procedures and completed the required chain-of-custody documentation.

D.4 RADIOLOGICAL ANALYSIS D.4.1 GROSS ALPHA/BETA Smears were counted on a low-background proportional counter for gross alpha and beta activity.

The minimum detectable activity of the procedures is approximately 11 dpm/100 cm2 for alpha and 14 dpm/100 cm2 for beta.

D.4.2 GAMMA SPECTROSCOPY Samples were analyzed as received, mixed, crushed, and/or homogenized as necessary, and a portion sealed in a 0.5-liter Marinelli beaker. The quantity placed in the beaker was chosen to reproduce the calibrated counting geometry. Net material weights were determined and the samples counted using intrinsic, high purity, germanium detectors coupled to a pulse height analyzer system. Background and Compton stripping, peak search, peak identification and concentration calculations were performed using the computer capabilities inherent in the analyzer system. All total absorption peaks (TAPs) associated with the ROCs were reviewed for consistency of activity. Spectra were also reviewed for other identifiable TAPs. TAPs used for determining the activities of ROCs and the typical associated MDCs, based on one-hour count time were:

Table D.1 TAPs for Determining Activities a

Radionuclide TAP (MeV) MDC (pCi/g)

Co-60 1.173 0.06 Cs-137 0.662 0.05 a Spectra were also reviewed for other identifiable TAPs.

Rancho Seco Confirmatory Survey Report D-4 5293-SR-01-0

D.5 DETECTION LIMITS Detection limits, referred to as MDCs, were based on 95% confidence level. Because of variations in background levels, measurement efficiencies, and contributions from other radionuclides in samples, the detection limits differ from sample to sample and instrument to instrument.

Rancho Seco Confirmatory Survey Report D-5 5293-SR-01-0

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