The End Of 3 He As We Know It

Transcription

1 The End Of 3 He As We Know It Richard Kouzes Pacific Northwest National Laboratory BES Detector Workshop August 1-3, 2012 PNNL-SA-89037

2 3 He Applications 3 He is a rare isotope with important uses in: Neutron detection " science " national security " safeguards " oil/gas exploration " Industrial applications Low-temperature physics Lung imaging Missile guidance Laser research Fusion 2

3 Current 3 He Supply By-product of nuclear weapons program Tritium decays with 12.4-year half-life to 3 He Tritium was produced for nuclear weapons in reactors U.S. tritium production ended in weapons needs met through recycling and reductions in the weapons stockpile Tritium production restarted in U.S. at Watts Bar reactor in 2007 only to support a smaller weapons stockpile U.S. 3 He made available through DOE Office of Science Russia is only other supplier of 3 He U.S. accumulated 200,000 liters of 3 He by the end of 1990s Demand was ~65k liters/year in 2009 Decay produces ~8,000 liters/year of 3 He in U.S. 3

4 U.S. Government Decisions (2010) Reduce Demand Evaluate performance standards - can 3 He per device be reduced Random movement of existing detectors Accelerate development and deployment of alternative technologies Manage Demand Suspend deployment of 3 He detectors in portal monitors Highest priority to uses that depend on unique properties Priority to uses taking advantage of major investments (e.g., SNS) Increase Supply Encourage 3 He recycling and reuse Increase 3 He extraction efficiency 3 He supply from other countries Russia, Canada, Korea, India? Investigate dedicated 3 He production from natural sources 4 Information from Steve Fetter, OSTP

5 CANDU Reactors New Supplies of 3 He? Discussions with Canada about possible supply from Ontario Power Generation CANDU (like) reactors: Canada (17+3), South Korea (4), India (15+3) Romania (2+3), China (2), Argentina (1), Pakistan (1) 3 He not currently extracted from natural supplies Primordial abundance of 3 He: 4 He was ~ 140 ppm Atmospheric abundance of 3 He: 4 He is ~1.4 ppm by volume About 1/500 fissions releases tritium Natural-gas has % He with 3 He: 4 He of ppm by volume (fission product + primordial) Solar wind is 4% He with 3 He: 4 He of ~480 ppm Lunar soil ( ppm of 3 He)? 5

6 3 He Demand Forecast In 2011 New supply from CANDU and/or Natural Gas? 6 Plot From Julie Bentz, National Security Staff

7 Workshops " Problem recognized in 2007 " NNSA (SRNL) " IEEE Nuclear Science Symposium " AAAS " IAEA " Safeguards " Science 7

8 Homeland Security Applications of Neutron Detection

9 Homeland Security Applications " Neutron Detection primarily for plutonium " Neutron background low; few sources of significant neutrons " Portal Monitors: one of largest users of 3 He " No further allocation for 3 He, must use alternatives 9

10 The Challenge: U.S. Ports of Entry Over 98% of all containerized cargo is now screened for radiation 307 Ports of Entry representing 621 border sites to protect Mail/ECCF Land Border Maritime Air Cargo " 332,622 vehicles per day " 57,006 trucks/containers per day " 2,459 aircraft per day " 580 vessels per day 10

11 11 Border Security Examples

12 RPM Concept of Operations Detect Confirm Isolate Primary Detection Secondary Detection Isolation Gamma Detectors Poly-Vinyl Toluene (PVT) Plastic Scintillators Neutron Detectors Moderated Helium-3 Gas Tubes 12 Identify Respond Identification of Isotope Seize/Arrest or Release Neutron Scan

13 13 Alarms and Nuisance Alarms Few sources of Neutron Alarms (~1/10,000) Troxler gauges, well logging sources, nuclear fuel, yellowcake Nuisance alarms: large gamma ray sources and ship effect Gamma Ray Nuisance Alarms (~1/100) agricultural products like fertilizer kitty litter ceramic glazed materials aircraft parts and counter weights propane tanks road salt welding rods ore and rock smoke detectors camera lenses televisions medical radioisotopes Troxler Gauge

14 Requirements for Neutron Detection for National Security " Plutonium emits detectable quantities of neutrons " Neutron alarms initiate a special Standard Operating Procedure " Neutron background arises from cosmic ray produced secondaries times smaller than gamma ray background " Physically fit in the volume currently occupied by the neutron detection assembly in existing systems " Fast and slow neutron detection required with flat response " Absolute efficiency per panel: є abs = 0.11% or 2.5 cps/ng 252 Cf " Minimum gamma ray discrimination ratio of better than 10-6 " Maintain neutron detection efficiency in presence of gamma rays: gamma absolute rejection ratio (0.9 < GARRn < 1.1) " Meet or exceed all ANSI N42.35/N42.38 requirements 14

15 Alternatives to 3 He for Neutron Detection

16 16 Alternative Neutron Detectors Proportional Counter Alternatives BF 3 filled proportional counters Boron-lined proportional counters Scintillator-based Alternatives Coated wavelength shifting fibers/paddles Scintillating glass fibers loaded with 6 Li Crystalline: LiI(Eu), LiF(W), Li 3 La 2 (BO 3 ) 3 (Cr), CLYC Liquid scintillator Semiconductor Neutron Detectors High efficiency, but limited in size Gallium arsenide, perforated semiconductor, boron carbide, boron nitride, pillar-structured detectors Other: doped glasses, Li-foil ion chamber, Li phosphate nanoparticles, fast neutron detectors

17 n Proportional Counters t p e 3 He 7 Li e Boron-lined n α

18 10 B Based Alternatives " Neutrons captured by 10 B yields α + 7 Li " BF 3 " Equivalent or better gamma discrimination than 3 He " Cross-section ~70% that of 3 He " Operates at low pressure (~1 atm) for reasonable HV " Requires multiple tubes for 3 He replacement " BF 3 is corrosive (hazardous gas): shipping regulations " Boron-lined proportional/straw tubes " Thin layer on tube wall to collect reaction products in proportional gas " Surface area limited, lower (<0.5) efficiency per tube than BF 3 " Requires configuration with many tubes " Safe, operates at low pressure (<1 atm) 18

19 Boron-Based Detectors Straw tube designs (Proportional Technology) Boron lined (Reuter Stokes) Multi-chamber boron lined approaches (LND) (Centronic) BF 3 (LND)

20 3 He and BF 3 Gamma Ray Sensitivity Pulse height spectra of 3 He tube in the presence of a large gamma source for five-minute integration period Multichannel analyzer limited to 1280 counts in each channel, cutting off noise peaks. BF 3 3 He Counts in 300 seconds Closed 10 mr/hr 20 mr/hr 40 mr/hr 100 mr/hr 200 mr/hr 400 mr/hr Counts Closed 10 mr/hr 20 mr/hr 40 mr/hr 100 mr/hr 200 mr/hr 400 mr/hr Channel Number Channel

21 Boron-Lined Gamma Ray Sensitivity Insensitive to 60 Co gammas (~10-8 ) Good neutron efficiency with gamma discriminating Alpha & Li Currents from B-lined Tube w/ threshold 252 Cf in Pig 2m from RSP Counts per emitted nerutron per 10keV 2.0E-06 Alpha Current Into Gas 1.8E-06 Li7 Current Into Gas 1.6E-06 Total Current Into Gas 1.4E E E E E E E E Energy Bins (MeV) 3 He

22 6 Li Based Alternatives " Neutron capture by the 6 Li yields α + 3 H " Glass fibers " 6 Li-enriched lithium silicate glass fibers doped with cerium which fluoresces (Bliss et al. 1995, PNNL) " Good efficiency (per unit surface area or neutron module) " Gamma-ray sensitive: discrimination with PSD " Coated wavelength shifting fibers " ZnS scintillator material mixed with 6 Li coating " Good efficiency (per unit surface area or neutron module) " Coating gamma-ray sensitive: Good discrimination with PSD 22

23 ZnS Plus 6 Li PMT t photons α plastic light guide ZnS+ 6 Li plastic light guide n Concept of layers of light guide and scintillator

24 ZnS + 6Li-coated Light-guide Detectors Paddles or fibers coated with ZnS scintillator mixed with 6Li Advantage Comparable performance to 3He tube(s) Disadvantages Gamma-ray discrimination as tested required improvement for fiber version Possible significant change to electronics Coated Paddles (Symetrica) Coated Fibers (IAT) Coated Paddles (SAIC)

25 Testing

26 26 PNNL Neutron Detector Testing " Measurements of neutron efficiency have been carried out at PNNL for standard deployable RPM systems " Testing of alternatives: " 3 He at pressures of 1.0, 2.0, 2.5 and 3 atmospheres " BF 3 filled proportional counter tubes (LND) " Boron-lined proportional counters (GE RS, LND, Centronic, Proportional Technology) " ZnS- 6 Li coated wavelength-shifting plastic fibers/paddles (IAT, Symetrica, SAIC) " Glass fibers loaded with 6 Li (Nucsafe)

27 Testing At PNNL: Requirements " Absolute efficiency per neutron module: " є abs = order of 0.11% efficiency per emitted neutron " Equivalent to 2.5 cps/ng 252 Cf at 2 meter standoff " Minimum gamma ray discrimination ratio of 10-6 " Maintain neutron detection efficiency in presence of gamma-rays " GARRn: Gamma Absolute Rejection Ratio (neutron) " Neutron efficiency measured with gammas / without gammas " Value needs to be within 10% (0.9 < GARRn < 1.1) 27

28 Summary of Technology Testing All options will require hardware and software modifications 3 He Technology Efficiency -discrim. Comments Gold standard BF3 Boron-lined Coated Plastic Paddles /Fibers Glass Fiber Hazardous, high operating voltage, more space Meets requirements Meets requirements Issues with neutron and gamma ray efficiency

29 Modeling and Simulation " Simulation guides investigation into alternatives and optimized configurations " 3 He and BF 3 tubes straightforward to model (reaction counting) " Boron-lined tubes more complicated, reaction product tracking required for accurate simulations " Requires newer versions of MCNPX " Models developed and verified with different approaches " Reaction counting in LiF/ZnS appears to be consistent with measurements using a scaling factor 29

30 30 Modeled Pulse-Heights for B-Lined Tube Reaction Products

31 31 Measured Response of GE Reuter Stokes Detector

32 Conclusions 32 Applications for 3 He are diverse with demand > supply There are no known alternative for some applications Alternatives being deployed for national security A lot of work remains to be done Four alternative neutron detection technologies tested: " Boron lined tube technology meets requirements " BF 3 meets requirements but hazardous gas " LiF/ZnS coated material technology meets requirements " Glass fiber technology needs improved gamma ray separation Model and simulation has been applied to alternatives Focus shifting to other applications " Backpacks and handhelds " Safeguards

33 Acknowledgements " Support for this work came from: " US Department of Energy: NA-22 & NA-24 " The US Department of Defense " The US Department of Homeland Security " PNNL 33

34 34 Backup

35 3 He Demand Forecast In 2009 Projected demand ~65 kl/y - Projected Supply ~10-20 kl/y Supply 35 Data From Steve Fetter, OSTP

36 The Global View 20 foot Shipping Container Traffic Per Year Megaport Deployments 36