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Concentration of Tritium in Liquid Samples by Electrolysis

Concentration of Tritium in Liquid Samples by Electrolysis. 17 th Annual RETS – REMP Workshop Stan Morton, Ph.D. June 27, 2007 Philadelphia, PA June 27, 2007. HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS. problem solved. Tritium. Heavy Isotope of Hydrogen

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Concentration of Tritium in Liquid Samples by Electrolysis

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  1. Concentration of Tritium in Liquid Samples by Electrolysis 17th Annual RETS – REMP Workshop Stan Morton, Ph.D. June 27, 2007 Philadelphia, PA June 27, 2007 HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  2. Tritium • Heavy Isotope of Hydrogen • 12.3 year half-life • Beta Decays to Stable He-3 • Low-energy Beta Particle • 18.6 keV beta-max • 5.7 keV beta-avg • Hydrogen and Tritium interchangeable HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  3. Tritium Unit (TU) TU ≡ 0.118 Bq/L ≡ 3.19 pCi/L Or 1 Bq/L ≡ 8.47 TU 1TU ≡ Concentration of 10-18 HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  4. Sources of Tritium • Cosmogenic • Nuclear Weapons – Atmospheric detonation • By-Product Nuclear Power Reactors • Boron • Lithium • Fission Process HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  5. Cosmogenic • Spallation – Cosmic-rays interact with atomic nitrogen: 14N (n, 3H) → 12C • Reaction altitude from 11 to 16 km • Adds to Precipitation Level HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  6. Nuclear Weapons - Atmospheric • Testing 1940s through 1970s • Precipitation Levels peaked in 1963 • Additional 52 X 1018 Bq to Global Inventory • Estimated remnant of 100 – 400 pCi/L in precipitation HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  7. Precipitation Concentrations HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  8. Tritium Production from Boron • Boron-10 (19.9%) high thermal neutron cross section – 3835 barns • Control rods for BWRs and PWRs • Chemical shim and reactivity control in PWRs 10B(n,2α) → 3H 10B(n,α) → 7Li(n,nα) → 3H HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  9. Tritium Production from Lithium • Most acceptable hydroxide for pH control in some PWR primary coolant • 6Li (7.5%) 940 barns • Principle reactions: 7Li(n,nα) →3H 8Li(n,α) →3H HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  10. Tritium from Fission • Lesser extent from fission • Fission yield for 235U is ~0.01% HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  11. Tritium Inventory • Estimated normal releases 0.02 x 1018 Bq/year • Estimated off-normal releases 0.001 x 1018 Bq/year • Steady-state buildup 0.4 x 1018 Bq globally • Legacy release 0.4 x 1018 Bq/year • Steady-state buildup 7.4 x 1018 Bq globally HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  12. Tritium Global Inventory • Atmospheric detonations 50s & 60s: 185 to 240 X 1018 Bq • Legacy today: 52 X 1018 Bq • Combined natural and anthropogenic global inventory of approximately: 53 X 1018 Bq or ~ 10 Bq/L HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  13. Regulatory Limits • Weak beta and rapid elimination produce a minor constituent in dose evaluation • EPA 1976 Drinking Water Standard is 4 mrem/yr = 20,000 pCi/L • 1991 4 mrem/yr = 60,900; retained 1976 limit. HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  14. Dose Considerations • Human retention studies provide three-component half-lives • 6 to 12 days – turnover of pool of body water • 10 to 34 days – involved in carbon-tritium chemistry • 130 to 550 days – organic molecules with slow turnover rates HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  15. Perception vs. Risk • Braidwood – 1600 pCi/L ≡ 0.3 mrem/yr; Exelon Corporation bought the farm • Decatur Daily headline: …TVA, NRC are ‘flippant’ over tritium leaks • Morris Daily Herald: Dresden leak levels 25 times the allowable drinking water limits • Arizona Republic: Palo Verde’s tritium leak may impact the groundwater. • Harford Courant: Haddam a few gallons a day of tritium contaminated water breaches 6-foot thick concrete wall. HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  16. Concentration of Tritium by Electrolysis • 2006, GEL Labs recognized need • Quantitative below 150 – 200 pCi/L • Reliable method • Well defined turn-around-times • Quality driven • Customer service HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  17. Concentration of Tritium by Electrolysis • Exploits slight differences in physical properties between hydrogen and tritium • Molecule of water containing hydrogen more likely to dissociate by electrolysis than molecule of water containing tritium. HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  18. Overview • Aliquant of 500 mL sample screened for ‘high’ levels of tritium and extraneous emitters • Shipped to Richland Service Center (RSC) in Richland, Washington • Enrichment process • Returned in closed vial for LSC HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  19. Ambient and Environmental Considerations • All commercial analytical labs evaporate hundreds of liters of tritium laden water • May produce elevated levels of ambient tritium • Environmental concentrations vary by region • Eastern and Southern states highest levels • Mid-west and Western States lowest levels HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  20. Richland Service Center HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  21. Electrolysis Instrumentation HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  22. Electrolysis Cold-Water Bath HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  23. RSC Tritium Laboratory HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  24. Procedure • 300 mL distilled • 250 mL concentrated by electrolysis for maximum sensitivity • Batch size • 12 samples • 2 background • LCS containing NIST traceable tritium standard HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  25. Procedure (cont’d) • Cold water bath (~ 5°C) • Constant current until 25 mL remaining • Reduce current until 12 – 15 ml • Volume reduction and enrichment requires 12 – 14 days • Vacuum distillation to remove NaOH HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  26. Procedure (cont’d) • Volume determined by weight X = Vi / Vf • Enrichment determined from LCSs Y = Cf / Ci • Transferred to LSC vial • Returned to Charleston for beta counting HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  27. MARLAP Approach • Multi-Agency Radiological Laboratory Analytical Protocols (MARLAP) Manual • Nationally consistent approach to producing analytical data • Performance-based approach for selecting analytical protocol • Project specific criteria HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  28. MARLAP Method Validation HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  29. Newly Developed Methods • Newly developed use Level D or E • Increased number of replicates • Best estimate of precision and bias • Unique matrix HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  30. Determination of Uncertainty • Method validation determines method uncertainty • Sample uncertainty menu includes • Method uncertainty • Liquid-scintillation counting statistics • Background subtraction • NIST standards, decay time, half-life, etc. HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  31. Uncertainty Considerations • Uncertainty increases as activity approaches detection limit • Because of such effects, as analyte concentrations drop, the relative uncertainty associated with the result tends to increase, first to a substantial fraction of the result and finally to the point where the (symmetric) uncertainty interval includes zero. This region is typically associated with the practical limit of detection for a given method. HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

  32. Questions & Contact Information Contact Information: Stan Morton, Manager, Radiobioassay Programs 303.349.8345 stan.morton@gel.com Bob Wills, Manager, Nuclear Programs 843.556.8171 robert.wills@gel.com HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS problem solved

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