Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

U N C L A S S I F I E D Slide 1

Canberra NetCAM, Dynamic Radiation Source and CAM Alarm

Modeling

James T. VossJonathan A. Hudston

Tom McLean

RP-2 GroupLos Alamos National Laboratory

Los Alamos, NM, 87545

LA-UR-12-24875

Presented at 2012 HPIC Meeting,UNM-LA, Los Alamos, NMSeptember 24-26 2012

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

U N C L A S S I F I E D Slide 2

Introduction: Outline Introduction• Evaluation recap• Evaluation update• Suggested areas for future improvement

Current NetCAM performance• Alarm algorithms and set points

— Alarm modeling• Dynamic radiation source testing

Conclusions

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

U N C L A S S I F I E D Slide 3

Introduction Canberra NetCAM evaluation began 9/2008 at LANL• Selected as candidate for continuous air monitor at the RLUOB facility• Perceived advantages of NetCAM dongle over ASM1000

— Cost ($3.5 K cheaper than ASM1000)— Networking capability (built-in web browser)— Peak-shape fitting algorithm included

Immediate problems found with:• Hardware • Firmware• User interface• Intra and Inter-communications• Documentation incomplete

Spent next 3.5 years resolving these issues

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U N C L A S S I F I E D Slide 4

Introduction NetCAM dongle• Up to 8 CAM heads can be connected

— but 1:1 configuration selected for RLUOB• RS-232 output to PC ( terminal emulator) console program• RJ-45 ethernet connections (unit has built-in web browser)• Remote monitoring using RadHawk (RadNet-compliant) listener• Has wireless capability too ( not used at LANL)

AS1700 CAM head• 1700 mm2 PIPs detector• Efficiency of ~32% for electroplated distributed 239Pu source• Flow rates ~ 2cfm• Original firmware: version 1.10 (now have 2.4)

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

U N C L A S S I F I E D Slide 5

Canberra NetCAM

Panel PC functions as local display (runs embedded Win XP) Dongle configuration

2 RJ-45 ports RS-485 (to CAM head) RS-232 for console connection

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U N C L A S S I F I E D Slide 6

Recent issues and resolutions

Power supplies for Panel PC and NetCAM dongle not UL-listed• Also leakage voltage of >30v AC measured on dongle• Resolved using quality power supplies

Sigma-based DAC-h alarm limit not correctly calculated• Issue fixed by Canberra

Acute false alarm rate abnormally high• Issue identified through modeling of NetCAM performance (discussed later)• Issue fixed by Canberra

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

U N C L A S S I F I E D Slide 7

Canberra NetCAM

Extensive list of required fixes satisfactorily completed earlier this year• Now offers reliable, robust operation• Able to automatically reboot to restore normal operation • Couples low detection limits with low false alarm probability

Acceptance test passed 7/2012• Alarm response tests (acute and chronic)• Performance tests • Reliability tests

54 NetCAM units delivered to RLUOB facility in 8/2012• Additional 13 units purchased as spares

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

U N C L A S S I F I E D Slide 8

Future NetCAM improvements Revise calculation of sigma-based DAC-h alarm limit i.e. :

• Net TRU counts = Gross counts – sum of tail contributions• Variance in Net counts = Gross counts + sum of tail contributions

Modify automatic energy calibration scheme• Currently too restrictive and unable to locate or track 7.69 MeV peak

Modify performance test algorithm• Currently takes >7 minutes whereas ASM1000 took ~ 2 minutes

Allow user to select chronic analysis update frequency• Currently fixed at 4 minute intervals

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

U N C L A S S I F I E D Slide 9

NetCAM alarm algorithms: acute alarm Acute alarm solely resides with the Alpha-Sentry CAM head

• Based on a user-set count interval (6 - 60 seconds)

• Counts in TRU region (2.8 - 5.8 MeV by default) and Rn region (5.8 - 6.0

MeV by default) summed

• Alarm sounds if following conditions satisfied

- the number of counts per channel in the TRU ROI is twice that of the Rn ROI

- the number of TRU ROI counts exceeds the user-set minimum

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

U N C L A S S I F I E D Slide 10

NetCAM acute alarm set points

Traditional LANL acute alarm set points;• 12 second count time• 80 or more TRU ROI counts required to generate an alarm• Default ROI boundaries used

Experience has shown that these settings adequately prevent false alarms but are they optimal ?

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

U N C L A S S I F I E D Slide 11

Acute alarm optimization: Spreadsheet analysis tool

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U N C L A S S I F I E D Slide 12

Acute alarm optimization: Spreadsheet analysis tool

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

U N C L A S S I F I E D Slide 13

Acute alarm optimization: Spreadsheet analysis tool

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

U N C L A S S I F I E D Slide 14

Acute alarm optimization: Spreadsheet analysis tool

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

U N C L A S S I F I E D Slide 15

Acute alarm: Calculated 239Pu DAC-h activity at TRU count rates corresponding to 1 false alarm per year per 60 NetCAMs

Count time (s) Minimum TRU counts

Average cpm

Average 239Pu DAC-h*

6 16 160 14

18 24 80 7.0

30 29 58 5.1

* Assumptions: 2 cfm, 30% detection efficiency, DAC factor = 5E-12 μCi/cm3 and energy calibration is correct

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

U N C L A S S I F I E D Slide 16

Acute alarm: Calculated 239Pu DAC-h activity corresponding to detection probabilities of 50% and 95% per count interval

Detection Prob. = 50% Detection Prob. = 95%

t(s) TRUcounts cpm DAC-h TRU

counts cpm DAC-h

6 28 280 25 69 690 61

18 97 323 28 166 553 49

30 166 332 29 248 496 44

* Assumptions: 2 cfm, 30% detection efficiency, DAC factor = 5E-12 μCi/cm3

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U N C L A S S I F I E D Slide 17

Modeling of NetCAM alarm response

FORTRAN program written to simulate NetCAM performance

• Code samples background and TRU spectral distributions specified by user

• Respective total count rates independently set by user

• Poisson stats used for number of bkg. and TRU counts and associated energies per 6 second update frequency

• Both contributions are summed to form an integrated spectrum

• Performs acute and chronic alarm (Valley mode) analysis under conditions specified by user — analysis frequency, ROI settings, cycle time, alarm set points, etc …..— valley (tail-fitting) mode used for chronic analysis

• Both true and blind man’s differential approaches are considered

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U N C L A S S I F I E D Slide 18

Acute alarm modeling vs spreadsheet predictions

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U N C L A S S I F I E D Slide 19

Acute alarm: Calculated average time-to-alarm as function of average 239Pu DAC-h activity

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

U N C L A S S I F I E D Slide 20

NetCAM chronic alarm algorithms Blindman’s differential approach used for NetCAM chronic analysis

• Spectrum refreshed at end of each count cycle

Valley mode• Sequential exponential tail-fitting and subtraction of tail counts• Net counts in TRU ROI used to determine activity

— recent improvements avoid non-physical net TRU cpm results• Uncertainty calculation incorrectly implemented by Canberra

— grossly overestimates uncertainty in net counts— compensates by using a relatively small kσ factor

• Alarm sounds when the fixed DAC-h limit and sigma-based limit are exceeded— an analysis every 4 minutes and at end of count cycle

Peaks mode• Not seriously considered as default analysis mode after some early problems

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U N C L A S S I F I E D Slide 21

Chronic alarm modeling

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U N C L A S S I F I E D Slide 22

NetCAM alarm modeling: conclusions

Code appears to emulate NetCAM behaviour well

Predictions are dependent on background spectrum and count rate

Current number of TRU counts required for an acute alarm appears to be too conservative

Valley analysis mode capable of 239Pu detection limits of 2 DAC-h with negligible false alarm rates based on available Rn/Tn background data• Count cycle times of about 12 minutes appear optimal• Alarm response time can be as good or even better than true differential approach

if NetCAM algorithm allowed freedom to analyze data more frequently

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U N C L A S S I F I E D Slide 23

Dynamic radiation source

Problem:

• Evaluation of CAM heads (sensitivity, time-to-alarm)

— Currently dependent on radioactive aerosols

— Time intensive, expensive and requires specialized facility

Solution:

• Dynamic Radiation Source (DRS)— Mimics the challenge of plutonium aerosol detection

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U N C L A S S I F I E D Slide 24

Production DRS: Overhead view

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U N C L A S S I F I E D Slide 25

Introduction: Advantages of DRS

Provides non-specialized in-house testing

Low cost (~2K) versus ~10K per aerosol test

Multiple test scenarios with various CAMs

Reproducibility

Supports iterative development of CAM analysis algorithms

No contamination issues

Rn/Tn background spectrum also present

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U N C L A S S I F I E D Slide 26

DRS: Alpha Sentry/ASM1000 count rate variation

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U N C L A S S I F I E D Slide 27

DRS: Alpha Sentry / NetCAM dongle test data

15 minutes

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U N C L A S S I F I E D Slide 28

DRS: Alpha Sentry / NetCAM dongle test data

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U N C L A S S I F I E D Slide 29

DRS: Alpha Sentry / NetCAM dongle test data

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U N C L A S S I F I E D Slide 30

DRS: Alpha Sentry / NetCAM dongle test data

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U N C L A S S I F I E D Slide 31

DRS: Alpha Sentry / NetCAM dongle test data

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U N C L A S S I F I E D Slide 32

Result summary: Average time to alarm (2 DAC-h limit)

CAM Analysismode

Cycle time

(min.)Average time to

alarm (min.)Std. dev.

(min.)

AS-1700R / NetCAM Valley 2 10 2

AS-1700R / NetCAM Valley 9 11 2

AS-1700R / NetCAM Valley 17 10 2

AS-1700R / NetCAM Peaks 2 8 3

AS-1700R / NetCAM Peaks 9 9 3

AS-1700R / NetCAM Peaks 17 9 3

AS-1700R / ASM1000 Valley 15 15 0

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U N C L A S S I F I E D Slide 33

Conclusions

Canberra NetCAM now capable of providing reliable operation and protecting workers• low alarm limits coupled with low false alarm probability• optimized alarm set points can be calculated using modeling• example of an ultimately successful collaboration between vendor and customer

Further beneficial improvements to NetCAM are readily achievable

DRS shown to be a useful tool in evaluating CAM chronic alarm algorithms• Empirical data lends support to the modeling predictions.