ML052860220
| ML052860220 | |
| Person / Time | |
|---|---|
| Site: | Saxton File:GPU Nuclear icon.png |
| Issue date: | 10/07/2004 |
| From: | Bauer T Oak Ridge Institute for Science & Education |
| To: | Dragoun T Division of Regulatory Improvement Programs |
| References | |
| Job Code J3036, ORISE 04-1326 | |
| Download: ML052860220 (29) | |
Text
R C) R~II S HE OAK RIDGE INSTITUTE FOR SCIENCE AINID EDUCAT101N October 7, 2004 Mr. Thomas Dragoun NRR/DRIP U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406
SUBJECT:
FINAL REPORT-CONFIRMATORY SURVEY OF THE PENELEC LINE SHACK, SAXTON NUCLEAR EXPERIMENTAL CORPORATION, SAXTON, PENNSYLVANIA (DOCKET NO. 50-146; TASK 1)
Dear Mr. Dragoun:
The Environmental Survey and Site Assessment Program (ESSAP) of the Oak Ridge Institute for Science and Education (ORISE) performed confirmatory survey activities of the Penelec Line Shack at the Saxton Nuclear Experimental Corporation (SNEC) in Saxton, Pennsylvania, during the period July 7 through 8, 2004. Enclosed is the final report If you have any questions or comments, please direct them to me at (865) 576-3356 or Timothy J. Vitkus at (865) 576-5073.
Sincerely, Timoth J. Bauer Health Physicist Environmental Survey and Site Assessment Program TJB:kp Enclosure cc: S. Adams, NRC/NRR/OWFN 012E5 A. Adams, NRC/NRR/OWFN 12G13 E. Abelquist, ORISE/ESSAP T. Vitkus, ORISE/ESSAP File/0968 A4-oc P.0. BOX 117, OAK RIDGE, TENNESSEE 37831-0117 Operated by Oak Ridge Associated Universities for the U.S. Department of Energy ie~j '~d 1,O1I &J(05 101" 1
ORISE 04-1326 CONFIRMATORY SURVEY OF THE PENELEC LINE SHACK SAXTON NUCLEAR EXPERIMENTAL CORPORATION SAXTON, PENNSYLVANIA Prepared by T. J. Bauer Environmental Survey and Site Assessment Program Oak Ridge Institute for Science and Education Oak Ridge, Tennessee 37831-0117 Prepared for the U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation FINAL REPORT SEPTEMBER 2004 This report is based on work performed under an Interagency Agreement (NRC Fin. No. J-3036) between the U.S. Nuclear Regulatory Commission and the U.S. Department of Energy. Oak Ridge Institute for Science and Education performs complementary work under contract number DE-AC05-000R22750 with the U.S. Department of Energy.
Penclec Line Shack projects/0968/Reports/2004-09-14 Final Report
CONFIRMATORY SURVEY OF THE PENELEC LINE SHACK SAXTON NUCLEAR EXPERIMENTAL CORPORATION SAXTON, PENNSYLVANIA Prepared by: Date: /
T B
.J. , Project Leader Environmental Survey and Site Assessment Program Reviewed by )ate: Y" T. J. Vitku urvey Projects Manager Environmental Survey and Site Assessment Program Reviewed by :/1? i d) )° Date: iboc-4 C/A R. D. Condra, Laboratory Manager Environmental Survey and Site Assessment Program
/1/n~ D D,ate: 9 C Reviewed by: I] - A40e-A. T. Payne, Quality Manager /
Environmental Survey and Site Assessment Program Reviewed by: ate: 9/_64 E. W. Abelquist, Pr lD Environmental Survey and Site Assessment Program to-Penelec line Shack projects/0968/ReportsI2004-09-14 Final Report
ACKNOWLEDGMENTS The author would like to acknowledge the significant contributions of the following staff members:
FIELD STAFF T. L. Brown T. D. Herrera LABORATORY STAFF R. D. Condra J. S. Cox W. P. Ivey B. D. Nourse CLERICAL STAFF D. K. Herrera K. L. Pond A. Ramsey ILLUSTRATOR T. L. Brown Penelec Line Shack projects/0968/Reports/2004-09-14 Final Report
TABLE OF CONTENTS PAGE List of Figures ........................................... ii List of Tables ........................................... iii Abbreviations and Acronyms ........................................... iv Introduction and Site History............................................ 1 Site Description ............................................ 2 Objectives ............................................ 2 Document Review ............................................ 2 Procedures ............................................ 3 Findings and Results ............................................ 4 Comparison of Results with Guidelines ............................................ 5 Summary ............................................ 5 Figures ............................................ 6 Tables ........................................... 10 References ........................................... 13 Appendices:
Appendix A: Major Instrumentation Appendix B: Survey and Analytical Procedures Penelec Line Shack i projects/0968/Reports2004-09.14 Final Report
LIST OF FIGURES PAGE FIGURE 1: Location of the Saxton Nuclear Experimental Corporation-Saxton, Pennsylvania .................................................. 7 FIGURE 2: Penelec Line Shack Interior-Measurement and Sampling Locations ................... 8 FIGURE 3: Penelec Line Shack Exterior-Measurement and Sampling Locations .................. 9 Penclec Line Shack ii projectsL/0968/Reports/2004-09-14 Final Report
LIST OF TABLES PAGE TABLE 1: Surface Activity Levels, Penelec Line Shack Interior ..................................... 11 TABLE 2: Surface Activity Levels, Penelec Line Shack Exterior ..................................... 12 Penelec Line Shack projects/0968/Reports/2004-09-14 Final Report iii
ABBREVIATIONS AND ACRONYMS gi instrument efficiency Fs surface efficiency Etotal total efficiency bi number of background counts in the interval BKG background cm centimeter cm2 square centimeter cpm counts per minute Cv containment vessel d' index of sensitivity DCGL derived concentration guideline level DOE Department of Energy dpm/100 cm2 disintegrations per minute per 100 square centimeters ESSAP Environmental Survey and Site Assessment Program FSS final status survey GPU GPU Nuclear, Inc.
ISM Integrated Safety Management ISO International Standards Organization ITP Intercomparison Testing Program JHA job hazard analysis keV kiloelectron volts LTP license termination plan MAPEP Mixed Analyte Performance Evaluation Program MARSSIM Multi-Agency Radiation Survey and Site Investigation Manual MDC minimum detectable concentration MDCR minimum detectable count rate MeV million electron volts min minute mm millimeter MWTh megawatt thermal NaI sodium iodide NIST National Institute of Standards and Technology NRC Nuclear Regulatory Commission NRIP NIST Radiochemistry Intercomparison Program NRR Office of Nuclear Reactor Regulation ORISE Oak Ridge Institute for Science and Education PWR pressurized water reactor sec second SNEC Saxton Nuclear Experimental Corporation Penellec Line Shack iV projects/0968/Rcports/2004-09-14 Final Report
CONFIRMATORY SURVEY OF THE PENELEC LINE SHACK SAXTON NUCLEAR EXPERIMENTAL CORPORATION SAXTON, PENNSYLVANIA INTRODUCTION AND SITE HISTORY The Saxton Nuclear Experimental Corporation (SNEC) facility, built from 1960 to 1962, was licensed to operate a 23.5-megawatt thermal (MWTh) power pressurized water reactor (PWR).
Initial criticality was reached on April 13, 1962 and the facility was shut down on May 1, 1972 after three fuel cycles were completed for a total of 1,005 effective full power days. At shutdown, the facility was placed into a state similar to the now defined U.S. Nuclear Regulatory Commission (NRC) "SAFSTOR" status. The reactor fuel was removed in 1972 and sent to the Atomic Energy Commission's, predecessor to the U.S. Department of Energy (DOE), facility in Savannah River, South Carolina. After the fuel was removed, equipment, tanks, and piping outside of the containment vessel (CV) were removed. From 1972 through 1974, buildings and structures that supported reactor operation were partially decontaminated. The SNEC facility has been maintained in a monitored condition since reactor shutdown.
GPU Nuclear, Inc. (GPU), a subsidiary of FirstEnergy Corporation, was formed in 1980, and became co-licensee with SNEC for the SNEC facility. GPU is currently decommissioning the SNEC facility on behalf of the site owner, SNEC. A variety of decommissioning activities have been performed at the SNEC site since 1980, which included but was not limited to the survey and demolitions of reactor support buildings and structures in 1992, the SNEC Soil Remediation Project completed in 1994, and the SNEC Large Component Removal Project completed in 1998. Most of the decommissioning focus since 1998 has been on the removal of support systems and interior CV concrete.
The Penelec Line Shack, Penelec Garage, Penelec Warehouse, and Penelec Switchyard Building are buildings located on property adjoining the SNEC facility property. While these structures were not directly associated with SNEC facility operation, SNEC used these buildings for storage, staging, and other such activities. A comprehensive final release survey of these buildings was performed from October 1988 to June 1989; however, since the time of the survey, decommissioning activities may have impacted these areas. All of the buildings except for the Penelec Line Shack projects/0968/Reports/2004.09-14 Final Report
Penelec Line Shack will be demolished, leaving it as the only structure remaining above ground on the SNEC site after the release of the site for public use. GPU used the guidance provided in the Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) to plan and perform the final status survey (FSS) of the Penelec Line Shack building (NRC 2000, GPU 2004a).
At the request of the NRC's Headquarters Office of Nuclear Reactor Regulation (NRR), the Oak Ridge Institute for Science and Education's (ORISE), Environmental Survey and Site Assessment Program (ESSAP) performed confirmatory surveys of the Penelec Line Shack.
SITE DESCRIPTION The SNEC facility is located at 165 Power Plant Road in Saxton, Pennsylvania (Figure 1). The only SNEC building remaining on the site is the Penelec Line Shack. All other remaining structures are temporary buildings used for decommissioning support activities. The Penelec Line Shack interior and exterior surfaces have been divided into 15 survey units with a total area of approximately 1,750 square meters. The building is constructed of sheet metal walls, steel roofing material, and a poured concrete interior floor. Other construction materials included masonite, cinderblocks, tile, and miscellaneous painted surfaces.
OBJECTIVES The objectives of the confirmatory survey were to provide independent contractor field data reviews and generate independent radiological data for use by the NRC in evaluating the adequacy and accuracy of the licensee's procedures and FSS results.
DOCUMENT REVIEW ESSAP reviewed the licensee's final radiological survey data for adequacy and appropriateness taking into account the license termination plan (LTP) and MARSSIM considerations (GPU 2004a and b and NRC 2000).
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PROCEDURES Survey activities were conducted from July 7 through 8, 2004 in accordance with a site-specific survey plan and the ORISE ESSAP Survey Procedures and Quality Assurance Manuals (ORISE 2004a, 2003, and 2004b). Appendices A and B provide additional information on the instrumentation and procedures discussed in this report including minimum detectable concentrations for field and laboratory instruments.
REFERENCE SYSTEM Measurements and sampling locations were referenced to the existing SNEC-established grid system or prominent building features.
SURFACE SCANS Interior and exterior surfaces were scanned for total beta radiation using gas proportional detectors and scanned for gamma radiation using NaI scintillation detectors. Total beta and gamma radiation scans were performed on approximately 100% of accessible areas of the floors and interior and exterior lower walls, up to a height of two meters-some areas were inaccessible due to shelving and equipment storage. Particular attention was given to cracks and joints of surfaces and other locations where material may have accumulated. All detectors were coupled to ratemeters or ratemeter-scalers with audible indicators. Locations of potentially significant elevated direct radiation were marked for further investigation.
SURFACE ACTIVITY MEASUREMENTS Direct measurements of building surfaces for total beta activity were performed at 30 locations which were identified by surface scans or corresponded to judgmental measurement locations (Figures 2 and 3). An area for determining construction material-specific backgrounds for the various materials of the building was not available on site; the off-site location SNEC had used in the past as a background reference area changed ownership and was no longer available.
Because construction material-specific backgrounds could not be determined, a shielded and unshielded measurement was performed at each location to correct for ambient gamma background contribution to the measurement count rate. Smear samples, for determining Pcnelec Line Shack projeczslO968/Rcports/2004-09-14 Final Report 3
removable activity levels, were collected from each direct measurement location. Measurements were performed using gas proportional detectors coupled to portable ratemeter-scalers.
SAMPLE ANALYSIS AND DATA INTERPRETATION Samples and data were returned to ORISE's ESSAP laboratory in Oak Ridge, Tennessee for analysis and interpretation. Samples were analyzed in accordance with the ESSAP Laboratory Procedures Manual (ORISE 2004c). Smears were analyzed for gross alpha and gross beta activity using a low-background gas proportional counter. Smear data and direct measurements for surface activity were converted to units of disintegrations per minute per 100 square centimeters (dpm/100 cm2).
Survey data were then compared with the site-specific derived concentration guideline levels (DCGLw) for the Penelec Line Shack. The primary contaminants of concern were beta-gamma emitters-fission and activation products-resulting from reactor operation. SNEC's NRC-2 approved gross activity DCGLw for surfaces of the Penelec Line Shack is 33,325 dpm/l00 cm (GPU 2004a).
FINDINGS AND RESULTS SURFACE SCANS Beta surface scans of the floors identified three areas distinguishable from background levels.
These areas noted on the floor were small in size, generally less than 300 cm2 in area. Gamma scans did not identify any indications of volumetric or subsurface contamination (i.e., gamma radiation levels were consistently within background ranges).
SURFACE ACTIVITY LEVELS Results of total and removable surface activity measurements for judgmental locations noted during surface scans and measurements performed at judgmental locations are provided in Table 1 for interior surfaces and Table 2 for exterior surfaces. Total beta surface activity ranged from -230 to 560 dpm/100 cm2 for both interior and exterior surfaces. Removable surface activity ranged from 0 to 3 dpm/100 cm2 for gross alpha and -5 to 4 dpm/100 cm2 for gross beta.
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COMPARISON OF RESULTS WITH GUIDELINES The contaminants of concern for this site are beta-gamma emitters resulting from the operation of the SNEC facility, with Cs-137 as the primary radionuclide. SNEC's NRC-approved gross activity DCGLw for surfaces of the Penelec Line Shack is 33,325 dpm/100 cm . No measurements exceeded the DCGLw.
SUMMARY
At the request of the U.S. Nuclear Regulatory Commission's Office of Nuclear Reactor Regulation, the Environmental Survey and Site Assessment Program of the Oak Ridge Institute for Science and Education conducted a confirmatory survey of the Penelec Line Shack at the Saxton Nuclear Experimental Corporation in Saxton, Pennsylvania. Confirmatory activities performed during the period July 7 through 8, 2004 included reviews of final status survey data, confirmatory scans, and direct surface activity measurements. Overall, the results of the survey activities confirmed that the radiological conditions of the Penelec Line Shack met the approved site-specific criteria.
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FIGURES Penelec Line Shack projects/0968/Reports/2004-09-14 Final Report
0968-001 (x)
+I NOT TO SCALE FIGURE 1: Location of the Saxton Nuclear Experimental Corporation - Saxton, Pennsylvania Penclec Line Shack 7 projects/0968/Reports/2004-09-14 Final Report
0968-002 (x)
SOUTH WALL
____ 20 177 52 6 Y 612 30 NORTH WALL MEASUREMENT/SAMPLING LOCATIONS e SINGLE-POINT LOWER WALLS AND FLOOR INACCESSIBLE AREA
+
N NOT TO SCALE FIGURE 2: Penelec Line Shack Interior - Measurement and Sampling Locations Penelec Line Shack 8 projects/0968/Reports/2004-09-14 Final Report
-
- 0968-003 (x)
NT W23 NORTH WALL 30 30 N_ _ _
28 SOUTH WALL AW eS EAST WALL WEST WALL MEASUREMENT/SAMPLING LOCATIONS NOT TO SCALE
- SINGLE-POINT LOWER WALLS FIGURE 3: Penelec Line Shack Exterior - Measurement and Sampling Locations Penelec Line Shack projects/0968/Reportsf2004-09-14 Final Report 9
TABLES Penelec Line Shack projects/0968/Reports/2004-09-14 Final Report
TABLE 1 SURFACE ACTIVITY LEVELS PENELEC LINE SHACK INTERIOR SAXTON NUCLEAR EXPERIMENTAL CORPORATION SAXTON, PENNSYLVANIA Total Beta Removable Surface Activity Location' Description Surface Activity (dpm/100 cm 2)
(dpm/lOOcm 2 ) Gross Alpha Gross Beta 1 Floor -40 0 -4 2 Floor 220 0 2 3 Floor 44 0 4 4 Floor 320 0 4 5 Floor 280 0 -4 6 Floor 410 3 -3 7 Floor 500 0 -3 8 West Wall 180 0 -2 9 South Wall -130 0 -3 10 East Wall 200 0 -2 11 North Wall -83 1 2 12 South Wall -230 0 2 13 South Wall -8 0 -4 14 East Wall 52 0 -2 15 North Wall 44 0 -2 16 North Wall -63 0 1 17 Floor 310 0 1 18 West Wall 130 1 2 19 North Wall 110 0 -3 20 Floor 560 0 -3 See Figure 2.
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TABLE 2 SURFACE ACTIVITY LEVELS PENELEC LINE SHACK EXTERIOR SAXTON NUCLEAR EXPERIMENTAL CORPORATION SAXTON, PENNSYLVANIA Total Beta Removable Surface Activity Location' Description Surface Activity (dpm/100 cm 2 )
(dpm/lOOcm 2 ) Gross Alpha Gross Beta 21 West Wall 48 0 -1 22 West Wall 71 1 -3 23 North Wall 180 1 -2 24 North Wall 120 0 1 25 North Wall 120 1 -3 26 East Wall 180 3 -4 27 East Wall 44 0 -2 28 South Wall 75 0 2 29 South Wall 110 1 -5 30 South Wall 140 0 2 aSee Figure 3.
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REFERENCES GPU Nuclear, Inc (GPU). Final Status Survey Report Saxton Nuclear Experimental Corporation Penelec Line Shack. Saxton, Pennsylvania; June 2004a.
GPU Nuclear, Inc. Saxton Nuclear Experimental Corporation Facility License Termination Plan.
Saxton, Pennsylvania; Revision 3, February 2004b.
Oak Ridge Institute for Science and Education (ORISE). Survey Procedures Manual for the Environmental Survey and Site Assessment Program. Oak Ridge, Tennessee; November 2003.
Oak Ridge Institute for Science and Education. Final Confirmatory Survey Plan for the Penelec Line Shack Building, Saxton Nuclear Experimental Corporation, Saxton, Pennsylvania (Docket No. 50-146; Task 1). Oak Ridge, Tennessee; June 30, 2004a.
Oak Ridge Institute for Science and Education. Quality Assurance Manual for the Environmental Survey and Site Assessment Program. Oak Ridge, Tennessee; January 2004b.
Oak Ridge Institute for Science and Education. Laboratory Procedures Manual for the Environmental Survey and Site Assessment Program. Oak Ridge, Tennessee; March 2004c.
U.S. Nuclear Regulatory Commission (NRC). Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM). Washington, DC; NUREG-1575; Revision 1, August 2000.
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APPENDIX A MAJOR INSTRUMENTATION Penclec Line Shack projects/0968/Reports/2004-09-14 Final Report
APPENDIX A MAJOR INSTRUMENTATION The display of a specific product is not to be construed as an endorsement of the product or its manufacturer by the author or his employer.
SCANNING INSTRUMENT/DETECTOR COMBINATIONS Beta Ludlum Floor Monitor Model 239-1 combined with Ludlum Ratemeter-Scaler Model 2221 coupled to Ludlum Gas Proportional Detector Model 43-37, Physical Area: 550 cm2 (Ludlum Measurements, Inc., Sweetwater, TX)
Ludlum Ratemeter-Scaler Model 2221 coupled to Ludlum Gas Proportional Detector Model 43-68, Physical Area: 126 cm2 (Ludlum Measurements, Inc., Sweetwater, TX)
Gamma Eberline Pulse Ratemeter Model PRM-6 (Eberline, Santa Fe, NM) coupled to Victoreen Nal Scintillation Detector Model 489-55, Crystal: 3.2 cm x 3.8 cm (Victoreen, Cleveland, OH)
DIRECT MEASUREMENT INSTRUMENT/DETECTOR COMBINATIONS Beta Ludlum Ratemeter-Scaler Model 2221 coupled to Ludlum Gas Proportional Detector Model 43-68, Physical Area: 126 cm2 (Ludlum Measurements, Inc., Sweetwater, TX)
LABORATORY ANALYTICAL INSTRUMENTATION Low-Background Gas Proportional Counter Model LB-5 100-W (Tennelec/Canberra, Meriden, CT)
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APPENDIX B SURVEY AND ANALYTICAL PROCEDURES Penelec Line Shack LneSackprojectsfO968/Reports/2004-09-14 Final Report Pencec
APPENDIX B SURVEY AND ANALYTICAL PROCEDURES PROJECT HEALTH AND SAFETY The proposed survey and sampling procedures were evaluated to ensure that any hazards inherent to the procedures themselves were addressed in current job hazard analyses (JHAs). All survey and laboratory activities were conducted in accordance with ORISE health and safety and radiation protection procedures.
Pre-survey activities included the evaluation and identification of potential health and safety issues through the use of a site-specific Integrated Safety Management (ISM) pre-job hazard checklist. A walkdown of the survey area was performed in order to evaluate and identify potential health and safety issues. Identified hazards fell under the existing JHAs.
CALIBRATION AND QUALITY ASSURANCE Calibration of all field and laboratory instrumentation was based on standards/sources, traceable to NIST, when such standards/sources were available. In cases where they were not available, standards of an industry-recognized organization were used.
Analytical and field survey activities were conducted in accordance with procedures from the following documents of the Environmental Survey and Site Assessment Program:
- Survey Procedures Manual (November 2003)
- Laboratory Procedures Manual (March 2004)
- Quality Assurance Manual (January 2004)
The procedures contained in these manuals were developed to meet the requirements of Department of Energy (DOE) Order 414.1B and the U.S. Nuclear Regulatory Commission Quality Assurance Manualfor the Office of NuclearMaterial Safety and Safeguards and contain measures to assess processes during their performance.
projects/0968/Reports/2004.09-14 Final Report Penelcc Line Shack B-1
Quality control procedures include:
- Daily instrument background and check-source measurements to confirm that equipment operation is within acceptable statistical fluctuations.
- Participation in MAPEP, NRIP, and ITP Laboratory Quality Assurance Programs.
- Training and certification of all individuals performing procedures.
- Periodic internal and external audits.
Detectors used for assessing surface activity were calibrated in accordance with ISO-7503' recommendations. The total beta efficiency (stotal) was determined for each instrument/detector combination and consisted of the product of the 2nc instrument efficiency (E;) and surface efficiency (es): stotal = ei x es.
Technetium-99 was selected as the calibration source as its maximum beta energy of 294 keV is lower than, thus conservative, compared to the maximum beta energy of 514 keV for Cs-137, the primary contaminant. ISO-75031 recommends an es of 0.25 for beta emitters with a maximum energy of less than 0.4 MeV (400 keV) and an Es of 0.5 for maximum beta energies greater than 0.4 MeV. Since the maximum beta energy for Cs-137 is greater than 0.4 MeV, an cs of 0.50 was used to calculate .totj.
Surface Scan Efficiencies Hand-held detectors were placed on contact with the calibration sources. A postulated hot-spot size of 100 cm2 was assumed a priorifor determining scanning instrument efficiencies. The scanning es value ranged from 0.31 to 0.34 for the hand-held gas proportional detectors, with the scanning etotal calculated to range from 0.16 to 0.17. Calibration source emission rates were not corrected for geometry when sources larger than the detectors were used.
'International Standard. ISO 7503-1, Evaluation of Surface Contamination - Part 1: Beta-emitters (maximum beta energy greater than 0.15 MeV) and alpha-emitters. August I, 1988.
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Surface Activity Measurement Efficiencies The static ci value for the single gas proportional detector used for the confirmatory survey surface activity measurements was 0.40; the static etStal was calculated to be 0.20. The calibration source emission rates were corrected to the physical area of the detectors when the source area exceeded the detector area.
SURVEY PROCEDURES Surface Scans Surface scans were performed by passing the detectors slowly over the surface; the distance between the detector and the surface was maintained at a minimum-nominally about 1 cm. A large surface area, gas proportional floor monitor and a Nal scintillation detector were used to scan the floors of the surveyed areas. Lower wall surfaces were scanned using small area (126 cm2) hand-held detectors. Identification of elevated levels was based on increases in the audible signal from the recording and/or indicating instrument.
Scan minimum detectable concentrations (MDCs) were estimated using the calculational approach described in NUREG-1507 2. The scan MDC is a function of many variables, including the background level. Typical beta background levels on floors and walls range from 800 to 1,400 cpm for the large surface area, gas proportional detectors (floor monitor) and from 250 to 450 cpm for the hand-held gas proportional detectors. Additional parameters selected for the calculation of scan MDC included a one-second observation interval, a specified level of performance at the first scanning stage of 95% true positive rate and 25% false positive rate, which yields a d'value of 2.32 (NUREG-1507, Table 6.1), and a surveyor efficiency of 0.5. To illustrate an example for the floor monitor and hand-held gas proportional detectors, the minimum detectable count rate (MDCR) and scan MDC can be calculated as follows:
bi = (250 cpm) (1 sec) (1 min/60 sec) = 4.2 counts MDCR = (2.32) (4.2 counts)*' [(60 sec/min) / (1 sec)] = 285 counts MDCRsurveyor = 285 / (0.5) "I = 403 cpm 2
NUREG-1507. Minimum Detectable Concentrations With Typical Radiation Survey Instruments for Various Contaminants and Field Conditions. US Nuclear Regulatory Commission. Washington, DC; June 1998.
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The scan MDC is calculated using the lowest calibrated hand-held gas proportional detector scanning 6 totaI of 0.16:
MDCRsuvw Scan MDC = surveyor dpm/100 cm 2 Clotal The scanning StOtal was determined for the floor monitor in the same fashion as above for the hand-held gas proportional detectors except typical efficiencies for the floor monitor were used rather than specific calibrations for this survey. The scanning es value for Tc-99 for the floor monitor was 0.24; the scanning Cjal was calculated to be 0.12. For the given backgrounds, the 2
estimated scan MDC range for the floor monitor is 4,500 to 5,900 dpm/100 cm ; and 2,500 to 3,400 dpm/nI00 cm2 for the hand-held gas proportional detector.
Specific scan MDCs for the Nal scintillation detector for Cs-137 in concrete were not determined as the instrument was used solely as a qualitative means to identify elevated gamma radiation for possible concrete sampling.
Surface Activity Measurements Measurements of total beta surface activity levels were performed using a gas proportional detector with portable ratemeter-scalers. Count rates (cpm), which were integrated over one minute with the detector held in a static position, were converted to activity levels (dpm/100 cm2 ) by dividing the net count rate by the total static efficiency (eixe,) and correcting for the physical area of the detector.
Surface activity measurements were performed on poured concrete, cinderblocks, tile, wall board, and corrugated metal. To account for the ambient gamma background, unshielded and shielded measurements were performed at each location. A 3/8-inch Plexiglas shield was used to determine the gamma count rate associated with the unshielded count rates. This thickness was demonstrated to block the beta particles from Sr-90, including the beta particles from the progeny Y-90. Since Y-90 emits beta particles higher in energy than Cs-137, the Plexiglas shield used completely shielded measurement of the Cs-137 beta emissions. Surface activity was Penelec Line Shack Peneec Final Report LnehackB-4projects/0968/Reports/2004-09-14 B-4
calculated by determining the net count rate, by subtracting the shielded measurement from the unshielded measurement, then correcting for total efficiency and detector area size.
The static beta MDC-calculated using the site background redetermination check-out count rate of 292 cpm-for the single gas proportional detector used for direct measurements was 330 dpm/100 cm2. The physical surface area assessed by the gas proportional detector used was 126 cm 2.
Removable Activity Measurements Removable gross alpha and gross beta activity levels were determined using numbered filter paper disks, 47 mm in diameter. Moderate pressure was applied to the smear and approximately 100 cm2 of the surface was wiped. Smears were placed in labeled envelopes with the location and other pertinent information recorded.
RADIOLOGICAL ANALYSIS Gross Alpha/Beta Smears were counted for two minutes on a low-background gas proportional system for gross alpha and beta activity. The MDCs of the procedure were 8 dpmlOO cm2 and 15 dpm/100 cm2 for gross alpha and gross beta, respectively.
DETECTION LIMITS Detection limits, referred to as MDCs, were based on 3 plus 4.65 times the standard deviation of the background count [3 + (4.65[BKG)]. 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.
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