Quality Assurance (QA) of OBT Quality Assurance (QA) of OBT Measurement in Environmental Samples Measurement in Environmental Samples September 12, 2011 Sang Bog Kim, Ph.D. Research Scientist Environmental Technologies Branch Chalk River Laboratories Chalk River, Ontario Canada 1 UNRESTRICTED / ILLIMITÉ
Outline 1. Background 2. Analytical Procedure 3. Previous OBT Inter-Laboratory Comparisons 4. CRL’s Experiments 5. Discussions UNRESTRICTED / ILLIMITÉ 2
1. Background • Environmental tritium pathways • Release and measurement • Recent tritium conferences • Lessons learned from Fukushima in Japan • Difference between HTO and OBT • HTO measurement • OBT history and definition • OBT classification • OBT measurement UNRESTRICTED / ILLIMITÉ 3
Environmental Tritium Pathw ays CNSC (2010) Tritium in the biological cycle of water UNRESTRICTED / ILLIMITÉ 4
Release ≠ Measurement • Environmental release forms are HT and HTO • Environmental measureable forms are HTO and OBT • HT → HTO → OBT • HTO measurement is relatively simple and straightforward • OBT behaviour in the environment is relatively complicated and has a higher uncertainty than HTO behaviour - OBT measurement is useful for normal operations - OBT prediction is useful for accidental situations UNRESTRICTED / ILLIMITÉ 5
Lessons Learned from Fukushima • Earthquake: Natural disaster • Tsunami: Natural disaster • Radiation: Man-made disaster • Are public very conservative or generous? • It is a time to reinforce environmental safety! UNRESTRICTED / ILLIMITÉ 6
Recent Tritium Conferences • EMRAS II in Vienna (2009 and 2010) • “Tritium 2010” in Japan (2010) • ICRER in Hamilton (2011) • OBT is a rising topic! UNRESTRICTED / ILLIMITÉ 7
Differences betw een HTO and OBT • Dose conversion factors (DCF) from ICRP HTO = 1.4 x 10 -11 Sv/Bq OBT = 4.2 x 10 -11 Sv/Bq • Retention time in biota • Half-life in humans • OBT/HTO ratios in environmental samples • Chemical forms • Dose contribution • Regulation guideline UNRESTRICTED / ILLIMITÉ 8
HTO Measurement • HTO and TFWT or THO (H 2 O form) • IAEA’s Inter-Laboratory Comparison (TRIC2008) • Certified Standard Material (Multi-Media RadCheMTM Assessment Program (MRaD) by Environmental Resource Associates (ERA)) • Drinking Water Guideline (7,000 Bq/L for Canada) UNRESTRICTED / ILLIMITÉ 9
OBT History and Definition • 70’s and 80’s : Tissue Bound Tritium (TBT) • Health Physics (1993) Special Issue : - Organically Bound Tritium (OBT) - Exchangeable Tritium - Non-exchangeable Tritium • EMRAS I and II : On-going topic - Carbon bound tritium (CBT) - XBT (X=N,O,S) - Buried Tritium • USA : Soluble and non-soluble OBT UNRESTRICTED / ILLIMITÉ 10
OBT Classification • Total OBT = Non-exchangeable OBT + Exchangeable OBT (Diabate and Strack, 1993) • OBT - Soluble OBT: Dissolved organic tritium (DOT) Tritiated organic (TO) Non-exchangeable OBT Exchangeable OBT - Insoluble OBT: Non-exchangeable OBT Exchangeable OBT - Buried tritium: Exchangeable OBT Non-exchangeable OBT • Biogenic (early metabolism) and abiogenic (late metabolism) UNRESTRICTED / ILLIMITÉ 11
Exchangeable and Non-exchangeable OBT UNRESTRICTED / ILLIMITÉ 12
OBT Measurement • Total tritium = Tissue free water tritium (TFWT) + OBT (Canada, France) TFWT TFWT OBT OBT • OBT = Total Tritium – TFWT (UK) - Wet combustion (?) UNRESTRICTED / ILLIMITÉ 13
2. Analytical Issues • OBT measurement scheme • HTO extraction • OBT measurement methods • Critical steps • Where we are! UNRESTRICTED / ILLIMITÉ 14
OBT Measurement Scheme UNRESTRICTED / ILLIMITÉ 15
TFWT Extraction • Freeze-drying system (Lyophilization) Laboratory design Commercial brand UNRESTRICTED / ILLIMITÉ 16
OBT Measurement Methods • Parr Combustion (U.S.A.) : Only available for plant and animal samples Detection limit is approximately 7-10 Bq/L UNRESTRICTED / ILLIMITÉ 17
OBT Measurement Methods • Tube furnace system: Soil samples for CRL UNRESTRICTED / ILLIMITÉ 18
OBT Measurement Methods • Plasma combustion: Germany UNRESTRICTED / ILLIMITÉ 19
OBT Measurement Methods • 3 He Mass Spectrometer: University of Ottawa UNRESTRICTED / ILLIMITÉ 20
OBT Measurement Methods • Oxidizer: Packard brand UNRESTRICTED / ILLIMITÉ 21
Critical Steps Critical Step Process Step 1 - Freeze-dry (water residue) - Oven-dry (temperature, duration) - Azo-distillation (old fashioned) Step 2 - Rinse (volume, duration) or no rinse - Combustion (Parr bomb, tube furnace) - Distillation (remove impurities) Step 3 - Liquid scintillation counter (Quantulus, Packard, Aloka) - Cocktail (Ultima Gold series) - Counting condition (background, time) UNRESTRICTED / ILLIMITÉ 22
Where w e are! • No Certified Reference Materials (CRMs) • No Standard OBT Procedures • IAEA and National Institute of Standard and Technology (NIST) • Quality Assurance (QA) • Quality Control (QC) UNRESTRICTED / ILLIMITÉ 23
3. Previous OBT Inter-Comparisons • Canada (CRL) • Canada (CRL, OPG, UO) • France • Japan • UK UNRESTRICTED / ILLIMITÉ 24
Canada (CRL) - Fusion Science and Technology 48, 762-766 (2005) :1998-1999 - Sample : Lettuce (approximately 990 Bq/L) and Crabapple (approximately 37 Bq/L) - Blank sample: Polyethylene beads (Alathon 1145, DuPont, USA) - Seven labs (Canada, England, France, Romania, Russia) - Parr combustion system (3 labs) and Quartz combustion tube system (5 labs) - Better agreement at higher OBT concentrations than lower OBT concentrations UNRESTRICTED / ILLIMITÉ 25
Canada (CRL, OPG, UO) - COG-09-3015 (2009) - CRL and OPG; CRL and UO - CRL ‘s measurement was lower than OPG and UO - Rinsing process and 3 He-ingrowth mass spectrometry UNRESTRICTED / ILLIMITÉ 26
France (CEA) Grass sample (2009) Grass sample (2010) UNRESTRICTED / ILLIMITÉ 27
Japan Swain liver sample Polished rice sample - Radioisotopes, 39 (1990) - 6 laboratories (5 use Quartz combustion and 1 uses plasma reactor) - Aloka LSC-LB (Teflon 100 ml vial and quartz vial) - Variation coefficients were 68% for the polished rice and 35% for the Swine liver UNRESTRICTED / ILLIMITÉ 28
UK (NCAS) - National Compliance and Assessment Service, NCAS/TR/99/003 (1999) - 7 Laboratories (Total tritium, tritiated water and OBT) - Aliquot sample (added tritium labelled sucrose) - This was not an environmental sample! UNRESTRICTED / ILLIMITÉ 29
4. CRL’s Experiments • Water residue • Furnace temperature • OBT in plants • OBT in animals • OBT in fish • OBT in soil • OBT/HTO ratio UNRESTRICTED / ILLIMITÉ 30
Water Residue (1) - From a commercial brand (Labconco) UNRESTRICTED / ILLIMITÉ 31
Water Residue (2) Fresh weight % after Freeze- % after Oven- Sample (g) dry (3 days) dry (1 day) Tomato 212 98.3 99.8 198 98.8 100 Lettuce 205 99.8 99.9 210 100 100 Beet 209 98.2 99.9 203 95.6 99.9 Average 206 ± 5.2 98.5 ± 1.6 99.9 ± 0.1 CRL’s procedure = Freeze-dry + Oven-dry (at 55ºC) UNRESTRICTED / ILLIMITÉ 32
Furnace Temperature - Pickering soil (P-2) UNRESTRICTED / ILLIMITÉ 33
OBT in Plants - Environmental Monitoring Results in 2009 UNRESTRICTED / ILLIMITÉ 34
HTO and OBT in Animals - CRL site and sites greater than 50 km from CRL UNRESTRICTED / ILLIMITÉ 35
OBT in Fish - Yearly sampling - In order to develop “Eco-metabolic tritium model”, MOU is being prepared between CRL and Romania. UNRESTRICTED / ILLIMITÉ 36
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