Modeling Atmospheric Releases of Molecular Tritium

1. Modeling Atmospheric Releases of Molecular Tritium 2005 RETS/REMP Workshop Jim Key Key Solutions, Inc. www.keysolutionsinc.com

2. Keep It? High Plant Inventories Worker Exposure Problem Increased Risk of Adverse Environmental Impact from Accidental Releases of High Concentrations TRITIUM Tritium Woes

3. Release It? Via Liquid Effluents? Lowest Dose Impact High Political Impact for Some Sites Via Gaseous Effluents? Higher Dose Impact Not ALARA Tritium Woes

4. Reg. Guide 1.109 and NUREG 0133 Models Indicate Significant Increase in HTO Dose for Atmospheric vs. Liquid Releases Exact Dose Increase is Site Specific but Typically 10 Times or Greater Significant Risk of Site Contamination (condensation on build surfaces, etc.) Dosimetric Impact of Liquid vs. Gaseous Releases of HTO

5. Why Not Release to Atmosphere as HT? Significantly Lower Dose Impact Canadian Technology – Electrolytic Decomposition of HTO to HT and O2 Canadians Release ~ 10 x More Tritium to Environment than U.S. A Different Idea

6. Radiotoxicity of HTO ~ 20,000-25,000 Times that of HT (ICRP-30) Only Significant Dose Impact Occurs Following Oxidation of HT to HTO and Subsequent Exposure Dosimetric Impact of HT vs. HTO

7. Need Ability to Predict Environmental Concentrations for Decision Making. If Tritium is Released Atmospherically as HT, then ODCM Must be Revised to Model Doses. Reg. Guide 1.109 and NUREG 0133 Assume Tritium Released in the Form of Tritiated Water – HTO Why Model Molecular Tritium?

8. AECL – Chalk River Laboratory, Canada 1986 – 18.5 Ci of HT Released Pure HT Release Savannah River Site, USA 1974 – 479,000 Ci of HT Released 1975 – 182,000 Ci of HT Released Estimated 99% HT, 1% HTO Short Term Releases Field Studies of AtmosphericHT Releases

9. IAEA Tritium Working Group Report - 2003 - “Modeling the Environmental Transport of Tritium in the Vicinity of Long Term Atmospheric and Sub-Surface Sources” Provides Comparison of Numerous Tritium Models Against Field Measurements BIOMASS-3

10. Models Atmospheric Releases of Molecular Tritium (HT) as well as Tritiated Water (HTO) These are all screening models and as such result in very conservative estimates of Tritium exposure. BIOMASS-3

11. AECL – Canada BEAK – Canada ANDRA – France CEA – France FZK – Germany ZSR – Germany JAERI – Japan NIPNE – Romania VNIIEF – Russia SESAB – Sweden LLNL – USA BIOMASS-3Examines Models Used By:

12. Oxidation in Atmosphere is Very Slow Process with Half Life of > 5 Years Most Significant Oxidation Occurs at the Atmosphere-Soil Interface HT HTO Oxidation of HT to HTO

13. Result of Bacterial Action in Soil Oxidation Efficiency is Highly Dependant on Organic Content of Soil Sterilized Clay Loam ~ 3.4% Natural Clay Loam 100% Occurs Very Quickly ~ hours Oxidation of HT to HTO in Soil

14. Described by “Deposition Velocity” - Vd Typical Values: 0.00003 to .00034 m/sec Allows Determination of Ground Plane Concentration (activity/m2) of HTO Resulting from Oxidation of HT Oxidation of HT in Soil

15. HT Has Approximately 6% Density of Air Might Seem that HT Would Quickly Diffuse Out of Plume Field Studies Have Shown that HT Remains Entrapped in Plume in the Near Field BIOMASS-3 Models All Model HT Dispersion Using Standard Gaussian Plume Model Atmospheric Dispersion of HT

16. Effective Ground Plane Deposition

17. Effective Ground Plane Deposition Rate

18. Soil Moisture Deposition of HT onto ground plane with subsequent oxidation to HTO. Airborne Concentration from Soil Re-Emission Emission of HTO (oxidized HT) into air from soil moisture. Physical TransportPathways Considered

19. Special Thanks to Ring Peterson at LLNL NEWTRIT Model Described in HPS Journal, Feb. 2002. Screening Model – Unrealistically Conservative DCART Model (unpublished internal LLNL report, Sept. 2004). Incomplete Model But Rather a General Approach More Realistic Assumptions Methodology Development

20. Methodology Presented Here Makes Use of DCART Strategy for Predicting Environmental Concentrations of HTO Due to Atmospheric Releases of HT Methodology Designed to be Compatible with Reg Guide 1.109 and NUREG 0133 Approaches Easily Incorporated into Current ODCM Methodology Methodology Development

21. Soil Moisture Concentration Where:   CSW,dep annual mean concentration of HTO in soil water deposition of HT.   3.15104 is 3.15107 sec/yr  10-3 m3/L. fr fraction of HTO retained in soil for plant root uptake (0.3). annual release rate of HT. Precip annual precipitation [m/yr].

22. Described in terms of HTO in air to HT in air based on field measurements. Specified in units of m3/L (e.g. pCi/L of HTO in air to pCi/m3 of HT in air) Note must multiply by: to get pCi/m3 HTO in air Airborne Concentration Due to Re-Emission

23. Defined for two heights above soil surface: grVeg 20 cm for vegetation uptake - typical value ~ 6 m3/L grInh 1.5 m for inhalation exposure - typical value ~ 4 m3/L Airborne Concentration Due to Re-Emission

24. Airborne Concentration Due to Re-Emission – Plant Exposure Where:   CR-air concentration of HTO in air due to re-emission of HTO in soil.   grVeg concentration ratio of HTO in air to HT in air at height of vegetation (20 cm) [m3/L]. HA absolute atmospheric humidity [kg/m3]. Water density of water [kg/L]

25. Concentration in Vegetation Where:   0.75 fraction of vegetation what is water [L/Kg].  ratio of vapor pressure of HTO and H2O (1.1).   HR relative humidity.

26. Airborne Concentration Due to Re-Emission – Inhalation Exposure Where:   airborne concentration of HTO in air at 1.5 m due to re-emission from soil. grInh concentration ratio of HTO in air to HT in air due to re-emission.

27. /Q = 110-6 sec/m3 Q = 1000 Ci/yr HA = 8 gm/m3 HR = 70% Precipitation = 30 inches/yr Dose Comparison Scenario

28. HTO vs. HT Predicted Dose

29. Both Appear to Have the Same Dose Impact Exact Comparison Requires Site Specific Analysis Obviously Is Not Cost Beneficial If Liquid Discharge is an Option Possible Option Where Liquid Releases Are Not Viable Liquid Release of HTO ofAtmospheric Release of HT?