Transuranic Air Filter Analysis Techniques

Transcription

1 Transuranic Air Filter Analysis Techniques S. Joseph Cope CNEC Fellow, PhD Student Advisor: Dr. Robert Hayes Consortium for Nonproliferation Enabling Capabilities (CNEC) Department of Nuclear Engineering North Carolina State University

2 Outline Scope and background Methods and materials Conservative TRU estimator model Results (Kernel density estimator) Gaussian superposition and deconvolution Next individual filter predictions Discussion and implications Conclusions and future work 2 Transuranic Air Filter Analysis Techniques S. Joseph Cope

3 Nuclear Assay in Radiological Emergency Response via Air Monitoring Goal: Graded approach for rapid, defensible TRU activity estimates Hours and days vs weeks for full radiochemistry Method: Field Deployable Portable Air Samplers with various single filter detection suites Gross alpha/beta, spectroscopic, and ROI Gas Proportional Counter PIPS detector (silicon) Phoswich Liquid Scintillation Radeye Handheld Probe Portable HPGe 3 Transuranic Air Filter Analysis Techniques S. Joseph Cope

4 Research Snapshot Rapid, defensible, conservative method for TRU activity estimation (Master s work) Graded Approach minutes hours days Handheld probe PIPS/Phoswich/LSC HPGe Truck/mobile lab analysis prioritize samples of interest for additional analysis or radiochemistry 4 Transuranic Air Filter Analysis Techniques S. Joseph Cope

5 Nonproliferation and Emergency Response Go/no-go decision levels with technical basis Cognizant to the technician and end user decision maker Introduce TRU check source to NORM background filter experiment Variations in geographic region, seasonal, diurnal and local weather conditions Goal: Continuing to engage more students and pursue mission critical data with national security implications 5 Transuranic Air Filter Analysis Techniques S. Joseph Cope

6 Scope A rapid, defensible, and conservative TRU activity estimate with an emergency response decision level for clearing air filter samples Radon and thoron are known interferents to TRU determination on air filters; concentrations are not constant over time or easily forward predicted Samples containing no TRU content compared to the expected value of zero activity Quantifies the bias of the long-lived thoron progeny to estimate the TRU activity on the filter rapidly 6 Transuranic Air Filter Analysis Techniques S. Joseph Cope

7 Naturally Occurring Radioactive Material 7 Transuranic Air Filter Analysis Techniques S. Joseph Cope

8 Anthropogenic and TRU Sources Planned releases (universities, power plants, labs) Detonations RDDs Accidents 8 Transuranic Air Filter Analysis Techniques S. Joseph Cope

9 Challenges to Radon Concentration Diurnal and seasonal variations Seftelis et al. Diurnal variation of radon progeny. Journal of Environmental Radioactivity Transuranic Air Filter Analysis Techniques S. Joseph Cope

10 Challenges to Radon Concentration Dependency on meteorological conditions Seftelis et al. Diurnal variation of radon progeny. Journal of Environmental Radioactivity Transuranic Air Filter Analysis Techniques S. Joseph Cope

11 Materials and Methods Grab sampling, 02 Dec Jan 2017 Gross alpha, 2 hr counting times in 5 min increments 23 paired experiments (46 filters total) Outside Research Building II, NCSU Centennial Campus Approximately 0.5 m between samplers, nominal flow rate 29.2 ± 1.6 LPM 11 Transuranic Air Filter Analysis Techniques S. Joseph Cope

12 Methods and Materials F&J Specialty Products Portable Air Samplers (Model DF-AB-75L and DF-AB-40Li) Bladewerx SabreISC (integrated sample counter) with 47 mm solid-state ion-implanted silicon detector FP47M glass fiber, 47 mm circular discs from F&J Specialty Products 12 Transuranic Air Filter Analysis Techniques S. Joseph Cope

13 Time and Length of Grab Sampling 23 dual (paired) experiments considered Samples of note for attribution of the 4 th Gaussian curve 13 Transuranic Air Filter Analysis Techniques S. Joseph Cope

14 Simplified Progeny Decay Equation yt ( ) = mexp( mt) + m m 1 estimates the radon progeny initial activity on the filter (Bq) m 2 estimates the effective decay constant folding in all of the radon progeny (min -1 ) Effective radon progeny t 1/2 ~ 30 min (NCRP 1988) m 3 estimates the TRU content on the filter (Bq) Expected value is zero ignoring thoron contributions 14 Transuranic Air Filter Analysis Techniques S. Joseph Cope

15 Conservative TRU Estimator (m 3 ) Among the short time scale of counting (~2 hrs), the thoron contribution, when present, is relatively unchanged (t 1/2 thoron ~ 10.6 hrs) The conservative m 3 folds in the thoron activity to the long-lived TRU estimate Thoron contribution builds up over sample duration compared to radon which saturates within 1-2 hours Samples known to be CLEAN (no TRU content) 15 Transuranic Air Filter Analysis Techniques S. Joseph Cope

16 Kernel Density Estimator (KDE) for m 3 Utilizing a KDE removes error associated with incorrect binning of mean values with known uncertainty and creates a continuous distribution for statistical analysis n 1 e KDE( x) = n σ i= 1 ( x µ ) 2 1 i 2 σi i 2π 16 Transuranic Air Filter Analysis Techniques S. Joseph Cope

17 Gaussian Fit and Deconvolution of the KDE Superposition of multiple Gaussian distributions Levenberg-Marquardt fitting provides error estimate 3 Gaussian Fit 4 Gaussian Fit 17 Transuranic Air Filter Analysis Techniques S. Joseph Cope

18 Gaussian Deconvolution of the KDE Previous work has attributed each Gaussian curve to a specific component of the experiment based on center and spread statistics rather than amplitude Novel fit of a 4 th Gaussian curve to account for positively biased anomaly in the KDE 0.18 Bq. 18 Transuranic Air Filter Analysis Techniques S. Joseph Cope

19 What is potentially a radical advance? Histogram of upper 95% confidence level for all individual TRU activity estimates using the fitted LM uncertainty for each filter All upper 95% TRU estimates are greater than zero; potentially a method for strictly conservative TRU activity estimates contained in a relatively small bias (<1.5 Bq) Two outliers omitted 19 Transuranic Air Filter Analysis Techniques S. Joseph Cope

20 Discussion Upper 95% estimate applied individually for each filter based on LM fitting; projected screening decision level for any individual filter, above which, a TRU activity hit is considered for the sampled times and region; Filters considered to be absent of abnormal TRU activity Results for TRU activity and Gaussian attributions match expectations from known physics and dispersion of radon and thoron progeny; The 4 th fitted Gaussian accounts for longer sampling periods and trends with the radon progeny concentration Higher thoron buildup over sampling time along with radon peaks in the morning hours due to temperature inversions 20 Transuranic Air Filter Analysis Techniques S. Joseph Cope

21 Emergency Response and Nonproliferation Rigorous uncertainty determination, even if large, allows for defensible emergency response decisions (evacuation) Rapid NDA screening technique to reduce the burden of throughput placed on limited radiochemistry resources Helps to prioritize samples for analysis before arrival to the lab Initial proliferation indicators screened quickly with quality Deconvolution of the KDE into Gaussians for each variability allows for hypothesis testing on individual contributions Discrimination of radionuclides with grossly different decay constants 21 Transuranic Air Filter Analysis Techniques S. Joseph Cope

22 Conclusions and Future Work Rapid filter counting methods allow defensible estimates Good for proliferation and emergency response screening Conservative 95% upper confidence level for a single filter at 0.4 Bq for seasonal and geographic interests with two locally disturbed samples omitted Assuming a representative characterization of the spread in radon/thoron concentrations, these results would be reproducible in similar geographical regions and times of year Seek to artificially introduce Pu-239 onto a filter counting experiment to simulate TRU content masked by the NORM buildup; analysis of alpha energy ROI for Pu Transuranic Air Filter Analysis Techniques S. Joseph Cope

23 Special thanks to Questions? See me at the poster session! S. Joseph Cope, This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number(s) DE-NA Transuranic Air Filter Analysis Techniques S. Joseph Cope