Introduction...1 Specifications... 1 Limitations... 1

Transcription

1 Table of Contents Introduction...1 Specifications... 1 Limitations... 1 New Algorithms...2 Regions of Interest... 3 New Algorithm ROIs... 3 Calibration... 5 Update Interval... 5 K Factor... 5 Subscripts... 6 Constants... 6 Variables... 7 Sigma Values and the Slow Alarm Alarms...14 N of M Alarm Logic Alarm Set-Points Flow Fail Noise Fast Alarm Slow Alarm Flow Alarm Pu DAC-hr Alarm Sensitivity...16 Recommended Alarm Set-Points Field Trials Radon Concentration Calculations Conclusions...20 References...21 Appendix A...22

2 ALGORITHMS ALPHA-6 CAM Introduction The Eberline ALPHA-6 Alpha Air Monitor Continuous Air Monitor (CAM) is designed to detect airborne alpha-emitting radionuclides collected on an internal filter using a silicon diffused junction detector. The CAM can calculate the activity of a specific radionuclide and subtract interferences from naturally-occurring background radioactivity by using the programmed equations and parameters. The Alpha-6 default setting is for the detection of Pu- 239 air concentrations. However, the Alpha-6 can be re-configured to detect various alphaemitting radionuclides. This Technical Basis Document discusses new, revised algorithms for the Alpha-6 CAM that are designed to detect Pu-239, Pu-238, and Am-241. Specifications The specifications of this CAM are as follows: Silicon diffused junction detector. Area = 490 mm 2, Diameter = 25 mm Filter holder designed for a 47 mm diameter filter. Millipore SM, 47 mm, 5 µm filter is recommended. A 25 mm filter holder is also used in some models. 256 channel analyzer Two 8-bit microprocessors Dot matrix liquid crystal display Twenty key keypad Mass air flow sensor Two serial ports Real time clock Lithium battery Beacon Bell Beeper External alarm Failure contacts The Eberline Alpha-6 CAMs located at Los Alamos National Lab (LANL) are of several configurations. The major differences include the inlet type, the Pu Constant, and the channels included in the Regions of Interest (ROI). Table 1 lists the various configurations. This paper uses the default configuration of the Alpha-6A-1, Version 1.21, in all references to the default. Limitations The ALPHA-6A-1 Alpha Air Monitor Technical Manual (Reference 1) lists the operating temperature range as 32 F to 104 F. The lower operating temperature limit can be a concern at Los Alamos since the normal winter temperatures range from 4 F to 31 F. Resolution of this issue can be as simple as heating the structures where CAMs are in service or heating the CAM. Page 1 of 24

3 ALPHA-6 CAM Algorithms Technical Basis Document RP-1 The upper operating temperature limit is not a concern since normal maximum temperatures in the summer at Los Alamos are approximately 67 F to 89 F. The record high temperature recorded in 1995 was 95 F (LANL 2007). Test data collected during CAM field trials has shown an occasional loss of data when the CAM resets the counters after power fluctuations. Utilizing surge suppressors or UPS systems can resolve this issue. Additionally radio frequency (RF) interferences may cause CAM false alarms. This interference can be prevented by use of a copper mesh Faraday cage built around the CAM or limiting the proximity between the CAMs and RF sources. For those CAMs with remote heads using a wire mesh around the signal cables will minimize RF interference. Table 1. Alpha-6 CAMs Default Configuration Variations Alpha-6A-1 Alpha-6 Alpha-6A Alpha-6A-1 Alpha-6 Version V1.21 V1.18 V1.18 V1.0 Energy vs. Channel Number A B A B Equation (Version used in Table 2) Pu-Constant (K Factor) Inlet Type Remote head, Clam shell Radial entry Remote inradial entry line head Sigma Slow Alarm Sigma Fast Alarm ROI 1 Channels ROI 2 Channels ROI 3 Channels ROI 4 Channels New Algorithms New algorithms have been developed to improve the monitoring capability and functionality of all configurations of the Alpha-6 CAMs. The new algorithms are designed to allow for the monitoring of Pu-239, Pu-238, and Am-241. The changes described in this document will decrease false alarm rates, decrease nuisance alarms, expand the monitoring capability of the CAM, and display two alarms in DAC-hr units which are more widely used and understood than sigma values that are used in the default settings. The fast alarm algorithm has been significantly revised to calculate Pu-239 DAC-hrs and to display the alarm value in DAC-hrs. The new alarm set-point is a fixed value instead of a sigma value (which was not fixed and was re-calculated with each data acquisition update). The new fast alarm does not utilize the sigma calculation. The fast alarm logic was also improved to decrease the likelihood of false alarms. Page 2 of 24

4 The concentration alarm algorithm has also been substantially revised. In the default setting, the concentration alarm did not activate the audible alarm or the beacon when an alarm set-point was reached. In the new algorithm, the concentration value is replaced by a Slow Pu DAC-hr alarm which activates the audible alarm and beacon when the alarm set-point is reached. Regions of Interest During operation, the CAM s multi-channel analyzer (MCA) collects counts in various channels depending on the energy of the incident alpha particle. The total counts in each channel are displayed as a spectrum. Regions of interest are defined as blocks of consecutive channels within the spectrum that are treated as a unit. Each algorithm, both default and the new algorithm, uses total counts within a ROI to determine the Pu-239 activity. The spectrum is divided into four ROIs that are delineated to identify the Pu peak and background peaks. The default algorithm is designed to measure Pu activity in the presence of radon and thoron progeny (background). These four ROIs section off portions of the Pu and background peaks as shown in Figure 1. Rather than considering the counts in a specific channel, the algorithms look at the total counts in a ROI. This allows the background counts to be subtracted from the Pu-239 counts. These ROIs represent portions of the Pu-239 peak (5.16 MeV), the Po-218/Bi-212 (6.0 MeV), and the Po-214 (7.68 MeV) peak. Po-218, Bi-212 Po-214 Po-212 Figure 1. Default Regions of Interest and radon background spectrum New Algorithm Regions of Interest As with the default algorithm, the spectrum is divided into four ROIs which are listed in Table 2. The new ROIs are designed to measure Pu-239, Pu-238, and Am-241 in the presence of radon and thoron progeny. The major change to the ROIs is in the definition of Region 2. Region 2 was modified to utilize a K factor of 0.17, which was calculated from data collected Page 3 of 24

5 during field trials. See the Algorithms Section for an explanation of the determination of the new K factor. Use of the new algorithm will result in standardization of the ROIs for all four configurations and versions of the Alpha-6 CAMs. According to the Alpha-6A-1 Alpha Air Monitor Technical Manual (Eberline 1991), the channel number in the Alpha 6 CAM is related to the energy (MeV) of the incident alpha particle. Two equations (depending on the MCA version in the CAM) are listed to determine the channel number as follows: Version A: Channel Number = 24.4 * [MeV-0.37], or Version B: Channel Number = 26 * [MeV-0.83] Regardless of which version is used, any energy value plugged into either Version A or B will result in the same channel number within a few channels. Refer to Section 2.3 Calibration for further clarification of channel number versus MeV. Table 2. New Algorithm Regions of Interest ROI Region Channels Energy Range of (MeV) Interest Version A Energy Range (MeV) Version B Description R Region Pu-238 (5.50 MeV ) and Am-241 (5.48 MeV ) at approximately Channel 121 Pu-239 (5.16 MeV) at approximately Channel 113 S Region Upper part of Po MeV peak T Region Lower part of Po MeV peak U Region Upper part of Po MeV peak V Region Po MeV peak W Region Upper guard ROI X Region Lower guard ROI Y Region Spectrum for channels 60 through 255 Z Region Entire spectrum There are certain factors that cause a complication with both the default and the new algorithm. The first is that the energy of the Pu-239 dominant alpha particle is 5.16 MeV (~channel 116 or 113 depending on the MCA version in the CAM). The ROI set by the both the default and new algorithms to count Pu-239 is overlapped by the tail from the Po-218/Bi-212 peak (6.0 MeV). Figure 1 illustrates how the Po-218/Bi-212 tail overlaps ROI 1. Page 4 of 24

6 The second factor is that the actual channel location of various peaks can vary due to the filterto-detector spacing, dust loading on the filter, aerosol burial depth within the filter, and air density. This variation in the channel location of the peaks should only be one or two channels. Greater variation in channel numbers may indicate the need to remove the CAM from use and recalibrate the detector. Calibration During calibration of the Alpha-6 CAMs at LANL, the position of the Po-214 peak (7.69 MeV) is adjusted to ensure that it is located in Channel 178, regardless of the version (A or B) of the energy equation utilized in a particular CAM. Regions 3 and 4 each cover a portion of the Po- 214 peak, as shown in Table 2. The counts in these ROIs are then used in the programmed algorithms. Therefore, the precise channel location of the Po-214 peak is important to the proper working of the algorithms. The detector efficiency is determined during calibration and the value is entered into the individual CAM. An efficiency of 22.5% is used in this document in the calculation of Variables B and C. Update Interval Both the default and the new algorithm use a 5-second update (data acquisition) interval. Every five seconds, the processor receives the total counts in each channel, then updates the following, in sequence: 1. Total present counts in each defined ROI 2. Calculation of the present flow rate 3. Calculation of the total sample volume 4. Pu-239 cpm 5. Pu DAC-hrs 6. Pu DAC concentration 7. Sigma cpm 8. Noise count 9. Difference between actual flow and the nominal flow rate 10. Display update 11. Checks alarm set-points to determine if there is an alarm condition The updates and calculations listed above are performed in a time period of 2 seconds. K Factor The formula used to describe the spectrum with no Pu present is as follows: Page 5 of 24

7 T K U Where: R S R = number of counts in ROI R S = number of counts in ROI S T = number of counts in ROI T U = number of counts in ROI U K = empirical constant K factor (default Pu algorithm constant) = 0.12 New K factor = 0.17 The K factor was determined empirically and helps to compensate for the changing peak shapes due to peak smearing during the data collection periods. From background data obtained during field trials, the new K factor of 0.17 was calculated. This K factor is used in the new algorithms. The K factor can easily be determined empirically if only radon and thoron are present, by using the following equation: R U K * S T If Pu is present, which contributes to the counts in R (ROI 1), the following equation applies: T K U R Pu S Where: Pu = Actual Pu-239 counts To solve for Pu counts: Pu R S K T U This equation subtracts the background contribution from the Pu channels. Subscripts In the equations used for the Alpha-6 CAM, subscripts 0-63 are entries for one second, with Subscript 0 indicating the most recent entry. Subscripts denote one-minute entries, with subscript 64 being the most recent. Page 6 of 24

8 Constants The Alpha-6 has up to five configurable constants. All five of the constants are assigned in the new algorithms. The constants are used for consistency between various equations and for ease when programming the algorithms. Table 3 lists the constants with default and new assigned values. Table 3. Constants Constant Description Default New 1 Nominal Air Flow (cfm) Spectrum acquisition interval (seconds) Pu Constant or K Factor The K Factor is used to resolve the differences between the ROI widths. 4 4 Pi Detector Efficiency* Varies Varies 5 DAC-hr conversion factor which converts from dpm to Pu-239 DAC-hr and to Pu DAC concentration (typically %) Not used 18.86** * The actual 4-pi detector efficiency, which is determined during calibration for an individual CAM, is used. RP-2 enters this 4-pi efficiency into the individual CAM. ** See Appendix A for calculation of the DAC-hr conversion factor. Variables Each user variable is defined by an equation that calculates the value of that variable using counts from various ROIs and constants. The default and new variables are listed in Table 4. Three of the five variables in the new algorithm have been revised. Variables B and C have been substantially revised while only minor revisions have been applied to Variable A. Variables D and E have not been revised and use the default equations. In order to program the new variables into the CAMs, Reverse Polish Notation (RPN) must be used. Equations for each of the new variables was converted into RPN, then entered into the CAM program. The RPN notation was verified by performing calculations using a hand-held calculator and comparing results to actual CAM results for each variable. Table 4. Default and New Variables Variable Default New A Pu-239 cpm Pu-239 cpm B Pu-239 counts Pu DAC-hrs C Pu-239 Concentration in pci/l Pu DAC conc D Noise cpm Noise cpm E Sigma cpm Sigma cpm Page 7 of 24

9 Variable A In both the default and new algorithm, Variable A calculates the Pu-239 cpm as defined by the given equation. Default (Pu-239 cpm) VARIABLE A New Variable A (Pu239 cpm) The expression (R - R 59 ) represents the increase in counts in region R over the last 60 seconds. The increase in counts over each of the regions - S, T, and U for the same time frame is used in the equation to compensate for the background radon contribution in order to determine the Pu-239 cpm. Pu 239 cpm R R Subscript 59 denotes history data. R 59 = the Pu-239 count 59 seconds ago. 59 K S U S 59 U 59 T T 1 59 This equation uses the increase in counts in a two minute time interval in Region 1 and subtracts the calculated background contribution. Note that the subscript 65 denotes two minutes previous and not 65 seconds. The value of 2 in the denominator converts the total counts collected in a two-minute time interval to counts per minute. Pu 239cpm R R 65 K S S65 T U U 2 65 T 1 The counting time has been extended to two minutes where the default interval is one minute. The increase in counting time improves the counting statistics and the detection level. 65 RPN Notation for Variable A: R,R(65)-,CONST(3),T,T(65)-,U,U(65)-,(1.0000)+/*,S,S(65)-*-,(2.0000)/ Page 8 of 24

10 Variable B Variable B is significantly revised in the new algorithm. The default assigns the Pu-239 counts to Variable B where the new algorithm assigns the calculation for Fast Pu DAC-hrs to Variable B. This variable is checked by the fast alarm algorithm to determine whether there is a fast alarm condition. Default (Pu-239 counts) In the default algorithm, Variable B is defined as the Pu-239 counts as follows: Pu 239 counts R Const(3) * T * S U Where: Const(3) = 1.2E-01 = Pu Constant or K Factor VARIABLE B New Variable B (Pu DAC-hours) Variable B is defined as the Pu DAC-hours and uses the following calculation based on Variable A, the detector efficiency, air flow rate, and the DAC-hr conversion factor. Pu DAC hrs A Const( 4) * I * Const(5) Where: A = the current Pu239 cpm Const(4) = the detector efficiency Const(5) = = Conversion factor used to convert from dpm to Pu-239 DAC-hr (see Appendix A for calculation of the conversion factor) I = Instantaneous air sampling rate in cubic feet per minute (cfm). RPN Notation for Variable B: A,CONST(4)/,I/,CONST(5)/ Page 9 of 24

11 Variable C Variable C has been extensively revised in the new algorithm. The new variable C calculates the Pu concentration in DAC instead of the Pu in pci/l. VARIABLE C Default (Concentration of Pu-239 in pci/l) New Variable C (Pu DAC concentration) Variable C is defined as the concentration of Pu-239 in pci/l. 5.3E 04 * B64 B94 B94 B124 Pu 239 Conc Const (4) * F79 F109 Where: 5.3E-04 is a conversion factor to convert ft 3 to liters, dpm to pci, and a time interval of 30 minutes to 1 minute. B 64 = the total Pu counts one minute ago (B 64 B 94 ) = Pu counts collected in the last 30 minutes (B 94 B 124 ) = Pu counts collected in the previous 30 minute period (F 79 F 109 ) = air volume increase over a 30 minute interval that ended 15 minutes ago. Variable C is defined as Pu DAC conc and by the following equation: Pu DACconc A(64) A(94) Const(4) * I * Const(5) * 2 Where: A = The change in Variable A in the most recent 30 minutes Const(4) = detector efficiency Const(5) = = Pu DAC Conversion factor used to convert dpm to DAC-hrs I = Instantaneous air sampling rate in cfm. 2 = Used to calculate the concentration based on a 30 minute interval. The calculation for Variable C is nearly identical to the calculation of Variable B (Pu DAC-hrs) and represents the concentration over a 30 minute period. RPN Notation for Variable C: A(64),A(94)-,CONST(4)/,I/,CONST(5)/,(2.0000)/ Page 10 of 24

12 Variable D Variable D accounts for noise such as electronic interference. The default equation is utilized in the new algorithm. VARIABLE D Default (Noise in counts per minute) Variable D is the noise in counts per minute (cpm). This equation sums the increase in counts in guard regions 6 and 7. Noise ( cpm) W W X X 59 Where: W = total counts in guard Region 6 W 59 = total counts 59 seconds ago in guard Region 6 X = total counts in guard Region 7 X 59 = total counts 59 seconds ago in guard Region 7 59 New Variable D (Noise in counts per minute) No change to this Variable. The default equation is also used in the new algorithm. RPN Notation for Variable D: W,W(59)-,X,X(59)-+ The noise equation considers the sum of the 60 second count increase in Region 6 plus the 60-second increase in Region 7. Variable E Variable E is the sigma cpm and is referenced to determine if there is an alarm condition for the Slow Pu alarm. Because this alarm set-point is based on the sigma value, which is calculated from the sum of both the Pu and background counts in various ROIs, the alarm set-point can vary with each count update. VARIABLE E Default (Sigma cpm) New Variable E ( cpm) R The new Variable E is identical to the default equation. No changes were made to the 2 K * T T equation that defines this variable. This is 59 R59 S S59 the only variable that utilizes the sigma U U 59 1 value. In determining whether there is a slow alarm condition, Variable A references Variable E. The default setting for the fast alarm is 6-sigma and the default for the slow alarm is 3-sigma. If Variable A > 3 sigma for 3 of 3 updates, then the slow alarm will be actuated. Note: Sigma is not used in the new algorithm for the fast alarm. RPN Notation for Variable E: R,R(59)-,CONST(3),T,T(59)-,U,U(59)-,(1.0000)+/*2^,S,S(59)-*+SQRT Page 11 of 24

13 Sigma Values and the Slow Alarm The sigma equation (Variable E) is the expression of the variability of the counts in the various regions as they affect the ability of the Alpha-6 to detect Pu in the presence of radon. As the background counts increase, the sigma value increases. Therefore, because the Slow Alarm references the sigma value, the actual alarm set-point increases as background counts increase. The sigma equation adds the background contribution to the Pu counts. Sigma refers to count rate, not the Pu concentration. Since the Slow Alarm depends on the sigma value, an increase in radon alone, Pu alone, or radon and Pu together could cause an alarm. Increases in radon values could result in increased false alarms. However, sigma is the square root of the variability of the counts being collected, which means that an increase in radon concentration by a factor of 10 would result in an increase of the sigma value by the square root of 10 (i.e., an increase by a factor of 3.2). Further, a hundred-fold increase in radon concentration, resulting in a hundredfold increase in counts collected, increases the sigma value by the square root of 100 (i.e., an increase by a factor of 10). Note that the +1 in the denominator of this equation is necessary to prevent division by zero should there be no counts in region U (Region 4, Po-214 peak region). If there are few counts in region U, the sigma value increases greatly. If there is no radon background, the equation condenses to the equation below, where only the counts in the Pu channels would be considered. ( 59 cpm ) ( R R ) Pucounts In the absence of radon, the sigma value is simply calculated as the square root of the counts in ROI 1 (Pu region). Since the slow alarm is set to 3σ, the total cpm in ROI 1 must be greater than three times the sigma value to cause an alarm. In the new algorithm, Variable A (Pu-239 cpm), references the alarm set-point for Variable E, which is 3 times Variable E (3σ) to determine if there is an alarm condition. When the cpm value calculated in Variable A is greater than 3σ, there is an alarm condition. Examples: A. Assume there are 16 cpm in the Pu region and there are no counts in the radon progeny channels (no Rn background): Variable A = 16 cpm Variable E = σ (cpm) = (16) = 4 cpm Alarm Set-point = 3* Variable E = 3σ = 12 cpm, and Because 16 >12 (Variable A > Alarm Set-point), this would be an alarm condition if the cpm is greater than 3σ for three 1-minute updates. B. Assume there are 9 cpm in the Pu region and there are no counts in the radon progeny channels: Variable A = 9 cpm Variable E = σ (cpm) = (9) = 3 cpm Alarm Set-point = 3* Variable E = 3σ = 9 cpm, and Page 12 of 24

14 Because 9 is not greater than 9, there would not be an alarm condition (Variable A is not greater than the alarm set-point). C. Assume there are 5 cpm in the Pu region: Variable A = 5 cpm Variable E = σ (cpm) = (5) = 2.2 cpm Alarm Set-point = 3* Variable E = 3σ = 6.7 cpm, and Because 5 is not greater than 6.7 (Variable A is not greater than the alarm set-point), there would not be an alarm condition. Alarms N of M Alarm Logic The N of M alarm logic requires the alarm condition to be true in N instances out of M updates. At each update interval, the alarm set-points are checked to determine if there is an alarm condition. If the N of M logic is set to 1 of 1, the alarm will sound as soon as the alarm condition is true for one update interval. If the N of M is set to 3 of 3, the alarm condition must be true for 3 consecutive update intervals before the alarm will sound. Alarm Set-Points The alarm set-points for the new algorithms are as follows: Flow Fail: Set-point: 0.3 cfm N of M: 3 of 3 Update time: 5 seconds The flow fail alarm is set to the default value. The alarm will initiate when 3 out of 3 checks indicate a flow of less than 0.3 cfm. Noise: Set-point: 100 cpm N of M: 3 of 3 Update time: 1 minute The alarm references Variable D to determine if there is an alarm condition. The set-point for this alarm is the same as the default setting. Fast Alarm: Set-point: The Fast Alarm and the Pu DAC-hr Alarm are based on Variable B. The Fast Alarm condition is checked each update (default is 5 second updates) and the Pu DAC-hr Alarm condition is checked each minute. In this document, two alarm set-points have been calculated which depend on the expected radon concentration. These are listed in Table 7. Only one alarm set-point can be programmed into the CAM at a time. If the radon concentration is known, an Page 13 of 24

15 alarm set-point can be calculated or the appropriate alarm set-point can be selected from Table 7. The Alarm Set-Point is 40 DAC-hrs. N of M: 3 of 3 Update time: 5 seconds The alarm references Variable B to determine if there is an alarm condition. Use of the 3 of 3 alarm logic helps decrease false alarms due to CAM upset conditions, such as electrical spikes. The new algorithm fast alarm set-points will cause a fast alarm when three consecutive five-second counts exceed the alarm set-point. The alarm will clear for any subsequent five-second count that does not meet the alarm criteria. Slow Alarm: Set-point: The set-point for the slow alarm is 3-sigma, regardless of the radon concentration. The Alarm Set-Point is 3σ. N of M: 3 of 3 Update time: 1 minute The slow alarm is set to the default value of three-sigma. The alarm variable is Variable A which references Variable E to determine if there is an alarm condition. No changes were made to the slow alarm setting. Flow Alarm: Set-point: (±) 0.20 cfm N of M: 3 of 3 Update time: 5 seconds This change from a default value of 1 +/ cfm will decrease the amount of time it takes to set the flow rate for each CAM. Additionally, this allows a greater flexibility in the acceptable flow rate. Pu DAC-hr Alarm: Set-point: In this document, two alarm set-points have been determined, which depend on the expected radon concentration. These are listed in Table 7. Only one alarm set-point can be programmed into the CAM at a time. If the radon concentration is known, an alarm set-point can be calculated or the appropriate alarm set-point can be selected from Table 7. The Pu DAC-hr Alarm Set-Point is 8 DAC-hrs. N of M: 3 of 3 Update time: 1 minute This alarm was previously the default Concentration Alarm and has been extensively revised to indicate Pu DAC-hr. This alarm activates the audible alarms and the beacon, unlike the default setting which only gives an indication on the screen that an alarm condition was reached. Tables 5 and 6 summarize the alarm settings, set-points, and alarm logic for the default settings and new settings. Page 14 of 24

16 Table 5. Summary of Default Alarm Settings Standard Alarm Names Default Set-Point Default Alarm Logic Update Time Flow Fail 0.3 cfm 3 of 3 5 seconds Noise 100 cpm 1 of 1 1 minute Fast Pu 6 Sigma 1 of 1 5 seconds Slow Pu 2.5 or 3 Sigma 3 of 3 1 minute Flow +/ cfm 3 of 3 5 seconds Concentration 0.2 pci/l 8 of 8 1 minute Table 6. Summary of New Alarm Settings New Alarm Names New Set- Point New Alarm Logic Update Time Comments Flow Fail 0.3 cfm 3 of 3 5 seconds Same as the default setting Noise 100 cpm 3 of 3 1 minute Same as the default setting Fast Pu 40 DAChrs 3 of 3 5 seconds Substantially changed from the default setting. Slow Pu 3 Sigma 3 of 3 1 minute Same as the default setting Flow +/ cfm 3 of 3 5 seconds The new setting expands the acceptable flow range Pu DAC-hr 8 DAC-hrs 3 of 3 1 minute Now called the Pu DAC-hr Alarm. Substantially changed from the default Concentration alarm. Activates the visual and audible alarms Sensitivity To test the performance of the new algorithm under actual conditions, four test CAMs were programmed with the new equations and alarm set-points. These CAMs were placed in TA-54/G Contamination Areas and Radiological Buffer Areas side-by-side with CAMs of Record which were programmed to the default algorithms. On a daily basis, data was downloaded from both the Test CAM and the CAM of Record at each location. From data collected during these field trials, radon concentrations were determined. Review of the data indicated several issues. In some instances, power fluctuations in TA-54 caused some of the CAMs to re-set which resulted in a loss of data. This data loss was corrected by reviewing the minute and hour data files and determining when the CAM was re-set. The counts recorded by the CAM were then converted to a count rate by applying the actual (corrected) time the counts were collected. In other instances, diesel exhaust particulates collected on the CAM detectors caused extraneous counts on some of the CAMs. These high counts resulted in unusually high radon concentrations when they were input into the radon calculations discussed in the Radon Concentration Calculations section of this document. Because of this issue, the radon concentrations determined during another study at LANL, which included TA-54, Page 15 of 24

17 (References 5 and 6) were used in developing alarm set-points. The radon concentrations determined from this study ranged from 0.3 to 2.9 pci/l over the LANL area and in TA-54 the concentrations were pci/l. Due to the issues with the CAM data collected during field trials, Poisson statistics were used to assist in developing the Fast Alarm set-points that would result in one (or less) false alarm per year considering the given radon concentrations. The following table lists radon concentrations and alarm set-points that would statistically result in one false alarm per year. Page 16 of 24

18 Table 7. Alarm Set-Points Leading to False Alarm Rate of One Per Year as a Function of Radon Concentration. Radon concentration (pci/l) False Alarm Rate/Year Fast Alarm Fast Alarm Set-Point (Variable B) (DAC-hrs) Slow Alarm Set-Point (Variable E) Pu DAC-hr Alarm Set-Point (Variable C) (DAC-hrs) Slow Alarm 3σ 3σ 3σ 3σ Pu DAC-hr Alarm 1.4 Not enough data Not enough data Not enough data To ensure the Slow Alarm set-point of 3-sigma was adequate, all radon data collected during field trials was placed in a spreadsheet and radon concentrations were calculated. Variable A and Variable E values were then calculated from the spectrum data. These values were compared to determine if Variable A exceeded Variable E, which would have resulted in a false Slow Alarm. In no instances did Variable A exceed Variable E. This means that the given radon values in Table 7 and for all the field data analyzed, there were no instances where the Slow Alarm would have been actuated. This verifies that no false Slow Alarms would be expected under the range of radon concentrations seen during the field trials. The Slow Alarm set-point of 3-sigma is adequate for a radon concentration range of 0 to 3.5 pci/l. Recommended Alarm Set-Points In order to determine appropriate alarm set-points the radon concentrations determined during field trials as well as results from radon studies conducted by other groups were reviewed. Additionally, regulations and 10CFR835 implementation guidance provided by DOE were reviewed. The recommended alarm set-points are as follows: Fast Alarm: 40 DAC-hrs Slow Alarm: 3σ Pu DAC-hr Alarm: 8 DAC-hrs These alarm set-points should be adjusted to a higher setting if radon concentrations are causing excessive false alarms. However, the determination of alternate alarm setpoints is left to the RP- 1 Team leader after a thorough review of the CAM data. The use of alternate alarm setpoints should be documented appropriately. Field Trials Two rounds of field trials were completed in TA-54-G where CAMs programmed with the test algorithms were placed side-by-side in selected areas with CAMs of Record that were programmed to the default algorithm. The test CAMs were appropriately labeled as such and the Page 17 of 24

19 alarms were disabled to ensure that any alarms and subsequent response were only related to the official CAMs of Record. Data was downloaded from both the CAM of Record and the test CAMs on a daily basis during the work week. Once data was downloaded, the filters were changed on the CAMs and other routine checks were performed. A total of eight CAMs were used in the testing as listed in Table 8. Page 18 of 24

20 Table 8. Field Trial CAMs and Locations CAM CAM # Location TEST 1 Dome 33 Radiological Buffer Area (RBA) RECORD 2 Dome 33 RBA TEST RBA RECORD RBA RECORD RBA TEST RBA RECORD Contamination Area TEST Contamination Area The first round of field trials resulted in unacceptable results and the algorithms were reworked. The next round of field trials utilized the algorithms described in this document. The results indicated an improvement over the default algorithms. Radon Concentration Calculations During field trials of the new algorithms, both Rn-222 (radon) and Rn-220 (thoron) progeny were found to be present as background interferences. This natural background concentration of both radon and thoron fluctuates. In order to determine the applicable alarm set-points for the CAMs, it was important to gather background data for several months and determine the range of concentrations. Data collected from February through May, 2008, was compared. To determine the Rn-222 concentration during the data collection time, the methodology cited in the User s Manual (Eberline 1991) was used. Assuming equilibrium, the concentration of Rn- 222 in air is equivalent to its first daughter product, Po-218 (RaA) concentration in pci/l. The maximum activity collected on the filter occurs when the number of newly collected atoms is equivalent to the number of atoms decaying each minute. The maximum Po-218 activity collectible on a filter is dependent on the concentration in air of Po-218 and the CAM volumetric flow rate. Po 218 cpm A max = Q C τ = Efficiency Where: A max = Maximum activity of Po-218 collectible on a filter Q = CAM volumetric flow rate (liters/min) C = Concentration of Po-218 in air (pci/l) τ = mean life = 1/λ, (Po-218 τ = 4.4 minutes) C = Po-218 (pci/l) = Eff Po 218 cpm (2.22) ( cfm) ( ) (4.4) Page 19 of 24

21 Where: Po-218 cpm = counts in ROI = Po-218 τ (mean life in minutes) = 1/λ Eff. = detector efficiency (~ 22.5%) converts from cpm to dpm cfm = flow rate in cubic feet per minute 2.22 = conversion from dpm to pci = conversion from cfm to liters/minute In determining the Rn-222 concentration, only the Po-218 counts are of importance. However, since both Po-218 and Bi-212 (a thoron daughter) have alpha energies at 6 MeV, the Bi-212 contribution to the total counts in ROI 1 must be subtracted. The Bi-212 contribution is proportional to the Po-212 value; therefore, a portion of the Po-212 counts in ROI 5 are subtracted from the ROI 1 counts. Although there is not an equilibrium condition between the radon-222 gas and the Po-218, an equilibrium of 85% is assumed for this methodology, (Eberline 1991), as shown in the following equation: Po-218 (pci/l) = ROI 1 cpm (( )( ROI 5 cpm)) = Rn-222 (pci/l) ( Const4) ( cfm ) (276.6) ( Const5) Where: = product of constants 2.22 x x 4.4 Const4 = Detector efficiency = c/d Const5 = Equilibrium constant, assumed to be 85% = quotient of Bi-212 branching ratios (35.94% of Bi-212 decays to Tl-208 and 64.06% decays to Po-212) Conclusions The new algorithm ROIs, equations, and variables worked well in field trials. The new alarm settings and read-outs in DAC-hrs are an improvement over the previous sigma values, since the DAC-hrs are more widely recognized and understood The Concentration alarm has been replaced by the new Pu DAC-hour alarm. The Concentration alarm used data in its calculations from the previous 60 minutes and therefore was not valid for the first 60 minutes after the spectrum and counters were reset. False alarms due to electronic noise have been minimized by the use of the N of M logic for all of the airborne alarms. The Fast Alarm has been reprogrammed to a DAC-hr alarm set-point instead of the default sigma value. Setting the sample air flow alarm limit to CFM has minimized the RCTs time required to adjust the sampling rate while still maintaining the air sampling rate within acceptable limits. Region 8 has been adjusted to cover channels 60 to 255. This allows the RCT to view almost all of the spectrum while minimizing the visual effect of a high noise level in the lower noise guard band. Since the vertical scale of the Alpha 6 spectrum auto ranges on the channel with the highest number of counts the radon/thoron and transuranic peaks were sometimes not visible when there were a lot of noise counts in the spectrum. Page 20 of 24

22 Test data collected during CAM field trials has shown an occasional loss of data when the CAM resets the counters after power fluctuations. Utilizing surge suppressors or UPS systems can resolve this issue. Additionally radio frequency (RF) interferences may cause CAM false alarms. This interference can be minimized by use of a copper mesh faraday cage built around the CAM or limiting the proximity between the CAMs and RF sources. For those CAMs with remote heads using a wire mesh around the signal cables will minimize RF interference. Nominal radon concentrations were used in calculations to determine the acceptable alarm setpoints that would result in one false alarm per year. Re-programming all Alpha-6 CAMs to the new algorithms will ensure consistency in the configurations and alarms, and improve worker understanding of the Alpha-6 CAM functions. Page 21 of 24

23 References 1. Eberline, (1991). ALPHA-6A-1 Alpha Air Monitor Technical Manual. Santa Fe, New Mexico. 2. Evans, R. D. (1980). Engineers Guide to the Elementary Behavior of Radon Daughters. Health Physics, Vol. 38, Hoover, M. D. and Newton, G. J. (1998). Performance Testing of Continuous Air Monitors for Alpha-Emitting Radionuclides. Radiation Protection Dosimetry, 79(1-4), LANL, (2007). Environmental Surveillance at Los Alamos during 2006, LA ENV, September McNaughton, M. (August 25, 2008) personal communication. 6. Whicker, J. (December 4, 2008) personal communication. 7. DOE G Air Monitoring Guide Page 22 of 24

24 Appendix A Determination of Conversion factor used to convert from dpm to Pu-239 DAC-hr Where: 5E-12 uci/ml = Pu-239 DAC 2.22E6 dpm/uci = conversion factor 1 cfm = liters/min = CAM flow rate 1000 ml/liter = conversion factor (5E-12 uci/ml)(2.22e6 dpm/uci)( L/min)(1000 ml/l)(60 min/hr) = dpm DAC-hr Page 23 of 24