Passive Whole Body Monitoring Application Note
Contents
1. Once the calibration is completed the unit needs to be alarm tested successfully and placed into service for approximately five minutes for background acquisition to occur prior to conducting testing for passive monitoring testing The Phantom CANBERRA currently uses a Livermore Realistic torso phantom for all passive monitoring test measurements it performs The prototype Livermore Realistic torso phantom was designed by Lawrence Livermore National Laboratory LLNL to accurately simulate the torso rib cage and lungs of a reference counting subject The phantom pictured in Figure 3 was manufactured by and purchased from Humanoid Systems Inc Figure 3 Livermore Realistic Phantom This phantom simulates the upper torso of a reference counting subject It extends from the base of the neck to just below the lower margin of the liver and is constructed without any head neck arm or lower torso components A durable soft tissue equivalent material is molded about a bone equivalent skeleton The interior thorax cavity is completely filled with removable organs and filler material to eliminate air spaces The inner organ components are accessible by removing the primary torso cover plate This primary cover plate contains a simulated sternum component and the balance of the simulated ribs Additional chest overlay plates can be used to simulate subjects with varying chest wall thickness values The overlay plates are primarily used f2. Once the MDA was determined 10 10 Contaminated indications the phantom and sources were left in the monitor in alarm test mode and individuals approached both sides of the monitor RCA and Clean Side until the self shielding from these individuals resulted in a Clean rather than Contaminated indication Each individual then moved back from the monitor in incremental steps until the monitor successfully enunciated an alarm Contaminated condition Setback lines can then be established to maintain the required passive sensitivity Once setback lines are established it is suggested that the same conditions be repeated during a routine shift change with the phantom be placed in the monitor with sources at or slightly above the MDA but less than 1 of an ALI to verify setback distances and monitor performance Again since the MDA and the units are less than 0 30 of an ALI once setback lines are established for the lower MDA the units can easily maintain their passive monitoring capability MDA Determination Incremental source activities are loaded into phantom lung set and the platform and phantom staged away from the monitor to avoid any influence on background acquisition The monitor is then placed into Alarm Test mode and the phantom and platform placed into the monitor Approximately 12 to 15 monitor cycles are allowed to complete to determine if the activity alarms the monitor After each attemp
3. an MDA to be the successful counts of an activity less than or equal to 1 of an ALI 10 out of 10 times for gamma emitters Perform at least 10 counts with each source strength leading up to the establishment of the MDA If multiple monitors are present within the same location determine if the monitors all behave in a similar fashion or if conditions due to shielding positioning will affect the MDA When in doubt consider testing of all additional monitors at that location e If the plant mix changes significantly based on your pre defined conditions to affect the passive monitoring you may need to repeat this testing You should reevaluate the use of passive monitoring equipment whenever analysis of the reactor coolant indicates that fuel leaks are present or have increased by a factor of 10 e Document the results of the testing by meeting formal administrative requirements and review approval cycles Including dates signatures review and approvals individuals performing reviewing and approving the results Other information including serial numbers of equipment including sources the location of the testing and orientation of the monitors List all conclusions and capabilities for the passive monitoring Gamma Detector High Voltage Optimization The high voltage of the plastic scintillators needs to be optimized for the best performance with the plant mix and or calibration sources Changing this high voltage affects t
4. A CANBERRA Application Note Passive Whole Body Monitoring Nuclear Power Industry Application Introduction to the Argos 5AB Zeus Gamma Option and the GEM 5 Gamma Exit Monitor CANBERRA s personnel contamination monitors the ARGOS 5AB with the Zeus plastic gamma scintillator option and the GEM 5 gamma exit monitor are used throughout the world s nuclear industry Typically these monitors are designed to detect surface contamination from alpha beta and gamma emitters however the units also have the capability to detect internal deposition at levels less than 1 of an annual limit of intake ALI when configured to alarm at the typical 5000 dpm beta 1000 dpm alpha and gamma activity of either 25 35 nCi 925 1295 Bq Co 60 or 65 75 nCi 2405 2775 Bq Cs 137 The passive monitoring can be easily accomplished in background fields of 10 25 uR h 100 250 nSv h using count times based on achieving the typical external surface contamination detection capabilities listed above The ARGOS 5AB with the ZEUS option as typically configured at many nuclear power facilities and as tested for this application note includes twenty four 24 gas flow proportional detectors three 3 large area gamma plastic scintillators a single gamma foot detector and the alpha beta moving head option A number of pictorial representations of the detector layout can be seen in Figures 1 and 2 An individual monitored upon exiting fro
5. Whole Body Count WBC A GEM 5 unit can also perform this function at the exit point to the Controlled Area This monitoring also provides a record of monitoring if the worker fails to return or complete their termination whole body count Setting up to perform and document the internal detection capability of passive monitoring should include the following elements e Outline a test plan and the steps needed to complete the testing Determine the sources available for testing the various combinations of sources to be used and the ratios of radionuclides that make up the typical plant mix Target various levels and work your way up from 0 1 to over 1 of an ALI A good series of increasing activities are from 0 1 0 2 0 3 0 5 0 75 1 and 1 5 e While a plant specific radionuclide mix is ideal Co 60 Co 58 and Cs 137 sources can be used Once the MDA is established for the gamma emitters the facility should use scaling factors to determine the total MDA given the plant mix and including hard to detects Use of a phantom setup which adequately represents the attenuation and self shielding behavior of a standard man A phantom with a variable chest wall thickness is desirable but using a thick chest wall will provide the most conservative results Evaluation and documentation of the self shielding effects of others standing in proximity to the monitors on the minimal detectable activities and establishing setback
6. distances to control these affects to achieve MDAs consistently less than 1 of an ALI Optimization of the gamma detectors high voltage to obtain the best overall efficiency for the representative plant mix of radionuclides Or using the monitor as configured and documenting the monitor s capabilities and limitations Configuring the monitor s software to perform the same in alarm test mode during testing as it would during routine personnel monitoring Using radioactivity standards traceable to the National Institute of Standards and Testing NIST or other equivalent testing laboratory for calibration alarm testing and testing with the phantom A detector calibrated with appropriate standards can also be used to assay sources used for passive monitoring capability Documenting both the detector background and the background exposure rates at the monitors present location A diagram with dimensions of the monitors location should also be made particularly in relationship to radiation sources if present Documenting the details of the phantom dimensions and other characteristics the location of the phantom in the monitor the location of the source loading in the phantom Photographic documentation of the setup shall also be generated Define the specific conditions for successful detection and what constitutes the Minimal Detectable Activity MDA for a system ANI constitutes the successful establishment of
7. es Self shielding of the gamma detectors by occupants in the monitors as well as individuals congregating near the monitors can artificially lower the background count rate seen by the gamma detectors While the ARGOS units can detect changing background during the actual count and notify an individual to re monitor based upon user defined statistical criteria people congregating near monitors during shift changes can artificially lower the overall background This is why stanchions and setback lines are typically seen at RCA and controlled area exit points around gamma sensitive personnel and tool object monitors The typical or average self shielding by an individual within the monitor can be set using a utility Optimize Self Shield Factors within the monitor s software enables the automatic setting of this self shielding factor This utility helps compensate for these effects Statistical settings for background re set and update are also available within the software to update this changing background Since the monitor adjusts the count time for each individual to meet a pre defined alarm setpoint this is not a problem for normal release criteria The monitor s count time is usually driven by the count time required for either the alpha and beta detection limits so under typical conditions the passive monitoring capability remains unaffected Figure 4 Sectioned lungs with radioactive disk source Once the self shielding c
8. g Implementation of a passive gamma monitoring program can help you to e Maximize performance of your facility controlled area and RCA monitoring equipment by performing passive gamma monitoring while simultaneously conducting surface contamination monitoring e Quickly identify personnel who need additional follow up and possible internal dosimetry evaluation e Augment your routine Whole Body Counting WBC program by identifying personnel who need additional investigational monitoring each time they leave the RCA and or the controlled area or minimize the routine counts performed using your whole body counting equipment e Retain a record of passive monitoring if a worker fails to return or complete their exit termination whole body count CANBERRA s ARGOS 5AB with Zeus Monitor and GEM 5 exit monitor have been demonstrated to fulfill Passive Monitoring capability when correctly implemented CANBERRA offers a Passive Monitoring Qualification and Evaluation service to help you to perform the plant specific activities necessary to take credit for your passive gamma monitoring program Please contact your sales representative to learn how Passive Monitoring can be implemented in your facility and to obtain customer references References 1 Institute of Nuclear Power Operations INPO INPO 05 008 Guidelines for Radiological Protection at Nuclear Power Stations 2005 2 American Nuclear Insurers ANI ANI Section 8 5 Rad
9. haracteristics have been determined for an average worker the phantom and the stand used to hold the phantom in position should be placed in the monitor and an assessment of the phantom stand assembly s self shielding determined As seen in Figure 5 the phantom and stand have been placed in the monitor Note that the platform holder has been designed to hold the torso at the same approximate height of a standard man CANBERRA s new AccuRate Morphological self shielding correction methodology performs such corrections on an individual basis and not just an average individual This method helps extend the monitor s passive monitoring capability to workers who deviate significantly from the norm In this case the self shielding properties of both the phantom and the support platform were determined to be comparable with a normal individual standing Figure 5 in the monitor The Phantom and platform platform s design while in the Argos meeting the self shielding characteristics also provided a stable surface which aided in the repeated positioning of the phantom weighing 60 Ibs after various source activities were loaded After the self shielding factors have been determined and loaded into the monitor software the phantom and platform are removed and the unit is placed into normal service and the background is allowed to collect for approximately 5 minutes 12100 17 1143 17 9 10089 17 o4 8
10. he sensitivity of the monitors as well as the background count rates and if changed after performance of the passive monitoring capability testing the impact of this change needs to be assessed The two radionuclides typically used for optimization in the US are Co 60 and Cs 137 Optimization with the lower energy Cs 137 increases the monitor s sensitivity to lower energy emitters such as I 131 or Tc 99m typically used for medical diagnostic scans A utility for optimization exists within the ARGOS and GEM 5 monitors based on a Figure of Merit FOM calculation Calibration of Alpha Beta and Gamma detectors Determination of the response of detectors calibration of all systems as tested for efficiency and activity alarm levels needs to be documented as the chosen alarm setpoints for typical personnel monitoring affect the performance sensitivity of passive monitoring If the alarm setpoints are changed or the unit re calibrated the affect on the passive monitoring needs to be evaluated Re calibration of the units plastic gamma scintillators unless a different radionuclide is used from that used during the initial performance testing or the efficiency deviates significantly decreased by gt 25 does not affect the ability of the monitors to achieve the 1 ALI sensitivity This is due to the fact that ARGOS with the Zeus option s MDA is typically less than 0 30 of an ALI More significant is the changing of the gamma alarm levels
11. iation Protection Bioassay 2008 3 Argos 3 5 Whole Body Surface Contamination Monitors User s Manual Canberra Industries 2010 4 HPS N13 30 1996 Performance Criteria for Radiobioassay 1996 ISO 9001 Zeus is a trademark of Canberra Industries Inc Argos and GEM are trademarks of Canberra Co CANBERRA Measurement Solutions for Nuclear Safety and Security CANBERRA is the Nuclear Measurements Business Unit of AREVA For more information please visit www canberra com C39962 11 12
12. m the RCA steps into the ARGOS 5AB and faces the detectors is guided into position with verbal and visual prompts is monitored on the front of the body and right hand arm the individual turns and positions with guidance and is monitored on the back of the body and left hand arm Passive monitoring sensitivity is increased when the unit is set to Monitor Body in Two Steps YES this enables the unit to sum the front and back gamma count results and take advantage of the longer count time In effect enabling the performance of a gross gamma whole body gamma count with sensitivity capable more than sufficient to complete passive monitoring In addition specific monitoring results both front and back count data can be linked to an individual worker through the use of an ID Badge reader which may take the form of a barcode scanner a magnetic card or a proximity card reader In this way each individual has a unique record which can be saved and archived In this application note the following topics will be covered The CANBERRA ARGOS 5AB with Zeus and GEM 5 Monitors Argos Monitor Shielding Monitor Software Guidance and Acceptance Criteria Practical Considerations for Passive Monitoring Optimization of Gamma Detector High Voltage Calibration of Alpha Beta and Gamma detectors The Phantom Determination of Typical Self Shielding and Setback distances MDA Determination Reliably Detectable Activity RDA Results Summar
13. more consecutive times to determine the MDA With the ARGOS unit this is confirmed by a visual display on the monitor seen in Figure 8 and accompanied by an audible Contaminated voice notification Figure 8 Typical Argos display during a successful contaminated event Reliably Detectable Activity RDA Results Results of the testing for Co 60 and Cs 137 yielded RDAs at this facility of 44 6 nCi 1650Bq or lt 0 23 ALI and 90 3 nCi 8341Bq or lt 0 07 ALI respectively These results were consistently obtained for four 4 ARGOS 5AB with Zeus gamma scintillators optimized for Cs 137 located at the same RCA exit point GEM 5 contamination monitors perform in a very similar fashion In the pause and wait mode they reach similar detection levels for passive monitoring and in the two step mode they can exceed the detection sensitivity of the ARGOS 5 Series monitors with the Zeus Option The gamma activity alarm set points for these units were all set at 25 nCi 925 Bq for Co 60 based on a point source efficiency calibration at 7 5 cm 3 in from the body surface detectors Surface contamination alarm set points were set at 4500 dpm beta and 1000 dpm alpha CE Summary ARGOS whole body contamination monitors with gamma detection capability and GEM 5 gamma exit monitors have been shown to detect intakes at levels less than 1 of the annual limit of intake ALI and are a resource to perform passive gamma monitorin
14. or calibrations of lung counters when measurements of transuranic radionuclides are made In these measurements the thickest overlay is used with the primary plate for a total average chest wall thickness of 39 1 mm Tests with and without the overlay were made when the MDA was reached and no changes in the MDA were observed when using either Cs 137 or Co 60 This phantom includes lung lymph node and abdominal inserts and is ideally suited for lung activity distribution calibrations The phantom can also be used as an appropriate blank with inert lungs to evaluate background counting levels and detection limits The lung inserts are sectioned to enable the placement of sources throughout the lungs as pictured in Figure 4 Sources may be distributed throughout the phantom lung set when multiple sources are used For single sources the sources should be placed in the center of each lung set towards the centerline of the phantom The distribution of the sources in either the left or right lung does not appear to affect the monitor s MDA The phantom is then reassembled and placed in the ARGOS supported by a stand in the monitor to simulate an individual during monitoring This phantom satisfies the HPS N13 30 1996 Performance Criteria for Radiobioassay standard for calibration and testing of counting systems for measurements of activity in the lungs Other phantoms may also be used Self Shielding Determination and Setback distanc
15. t the phantom and platform are removed and the monitor is taken out of service Alarm test files for each activity sequence are organized and filed The alarm test files provide a date and time stamped record of which detectors alarmed Figure 6 and Figure 7 the directory of Alarm Test Results files with _C indicating a contaminated determination The monitor is then placed back into service Figure 6 Contaminated determination in alarm test file EJ RESULT 20101025105446 AT _ TXT RESULT 20101025105509 AT _ TXT RESULT 20101025105520 AT _ TXT RESULT 20101025105531 AT C TXT RESULT 20101025105542 AT C TXT RESULT 20101025105554 AT C TXT RESULT 20101025105605 AT C TXT RESULT 20101025105616 AT C TXT RESULT 20101025105627 AT C TXT RESULT 20101025105639 AT C TXT RESULT 20101025105650 AT C TXT RESULT 20101025105701 AT C TXT RESULT 20101025105712 AT C TXT RESULT 20101025105724 AT C TXT RESULT 20101025105735 AT C TXT RESULT 20101025105746 AT C TXT RESULT 20101025105757 AT C TXT RESULT 20101025105809 AT C TXT AlarmTest Mode E RESULT 20101025105457 AT _ TXT _______ Phantom Moved into Position Alarm Test Mode Phantom in Position with 10 10 Contaminated Determinations Figure 7 Alarm test files in directory The source activity is increased in the phantom and the testing cycle is repeated until the monitor successfully registers Contaminated on one or more detectors 10 or
16. tillators weights typically less e The curtain wall provides shadow shielding for the plastic scintillators Argos Monitor Software The monitor software includes utilities and data collection and archiving capabilities which enable the easy collection of calibration self shielding and alarm testing data to properly record and document your passive monitoring capability Consult the User Manual and the CANBERRA Services and Application Support Group ASG for assistance or services to complete testing Applicable Guidance and Acceptance Criteria e The Institute of Nuclear Power Operations INPO and the American Nuclear Insurers ANI Regulatory bodies have acknowledged the performance of passive monitoring to either replace or augment routine whole body counting For example INPO states the following Passive monitors Some gamma sensitive whole body contamination monitors and portal monitors at the exits from the RCA and whole body counters are used to routinely monitor personnel for internally deposited radioactivity If passive monitoring is used to replace routine whole body counting evaluation and testing must be completed to determine the appropriateness and limitations of the program Testing should be plant specific and should not rely solely on evaluations done by other stations M e Similarly the American Nuclear Insurers ANI notes in ANI Section 8 5 Radiation Protection Bioassay The En
17. trance and Termination Whole Body Counts are preferred however credit may be taken for passive monitoring if internal sensitivity studies have been performed on the PCMs or PMs Specific performance criteria for the determination of monitor sensitivity are listed in section 8 5 9 and will be discussed in this application note 2 e What constitutes detection of lt 1 of an ALI Since an intake of radioactive materials via inhalation is larger than the actual retention and we are measuring the amount retained in the body when one performs either whole body counting or passive monitoring we need to adjust the quantity for detection success by the amount retained during the same day as the intake The intake retention fraction can be approximated 0 63 of the 1 of an ALI for the purposes of this calculation assuming a particle size of approximately 1u AMAD So for example the consistent detection of less than 192 nCi 7 1 KBq of Co 60 and less than 1276 nCi 47 2 kBq of Cs 137 would denote success based on an ALI of 30 and 200 uCi 1 11 and 7 4 MBq of Co and Cs respectively Practical Passive Monitoring Passive Gamma monitoring is not new but with CANBERRA s Zeus option it can be achieved simultaneously at the point of exit from the RCA while surface contamination monitoring is conducted Workers exiting the RCA are effectively monitored on at least a daily basis if not multiple times in lieu of a daily or routine
18. y The CANBERRA ARGOS 5AB with Zeus Monitor The Zeus Option on an ARGOS monitor consists of the following major components Figure 1 1 Three 3 large plastic gamma scintillators monitoring the body 2 A1 in 2 54 cm lead shielding curtain wall 3 0 4 in lead shielding surrounding the back and sides of the plastic scintillators A single plastic gamma head scintillation detector _ Gamma Detection Zeus Option a The Zeus opton adds full gamma detection capability Three large plastis scintillators monitor body coniarnination a Smaller scintillator monitors the head a Seintilaiors aro shialdad with 10 mm 0 4 in of lead 425 mm 1 0 in load urtan minimizes se shipiding affects Argos monitor with fous option Figure 1 Full Zeus Option on the Argos 5AB Typical field implementations have replaced the single gamma head detector with a gas flow alpha beta moving head detector and instead implemented a gamma foot detector option in the detector 1 position see Figure 2 Figure 2 Alternative layout gamma detectors in green The Shielding The complete shielding package includes both 2 5 cm 1 in curtain shielding wall and approximately 0 4 in of lead surrounding the plastic scintillators The lead features e Modular epoxy coated lead ingot design for ease of handling and installation e Each lead ingot weights approximately 20 Ibs The lead surrounding the scin
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