1 / 32

SRNS-F3200-2012-00019 Comparison of Parameters for Modeling Tritium Dispersion

This study compares the impact of MACCS2 input parameters on Tritium dispersion. The objective is to characterize the responses of these parameters, not to justify any particular value. The methodology involves establishing a baseline result and varying one parameter at a time. The study examines parameters such as plume depletion/deposition velocity, dispersion coefficients, and resuspension coefficients.

cbillings
Download Presentation

SRNS-F3200-2012-00019 Comparison of Parameters for Modeling Tritium Dispersion

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. SRNS-F3200-2012-00019 Comparison of Parameters for Modeling Tritium Dispersion Eric Hope Accident Analyst Nuclear & Criticality Safety Engineering Savannah River Nuclear Solutions, LLC April 18, 2012 2012 EFCOG Safety Analysis Workshop Santa Fe, New Mexico

  2. Savannah River Nuclear Solutions SRNS is the M&O contractor for DOE’s Savannah River Site in Aiken, S.C. The primary initiatives for SRNS are national security, clean energy and environmental stewardship. • We provide nuclear materials management to support national defense and U.S. nuclear nonproliferation efforts. • We support the National Nuclear Security Administration by extracting tritium and delivering products to military and weapons design agencies. • We develop and deploy environmental cleanup technologies. • We conduct technology R&D on national energy independence initiatives.

  3. Objective: Characterize the impact of MACCS2 input parameters on the result for a unit release of Tritium

  4. Objective: This comparison is intended to look at responses of parameters, not as justification for any particular value

  5. Methodology • Establish a baseline result • Vary one parameter at a time • Use a range that reflects current and anticipated requirements • Some parameters are essentially step functions

  6. Methodology • Baseline facility has large tritium inventory, small amounts of other species • Some activation products • No significant quantities of alpha emitting material

  7. Input Parameters MACCS2 requires user input of parameters – some are: • Plume Depletion/Deposition Velocity • Sigma Z adjustment for surface roughness • Sigma Y adjustment for time basis/plume meander • Dispersion Coefficients • Resuspension Coefficient

  8. Baseline for MACCS2 Calculations Conditions and parameters used in existing analysis: • Dry deposition with 0.5 cm/sec deposition velocity • Offsite receptor at 11.5 km from release • 95th dose quantile • Tadmor-Gur dispersion coefficients (far field) • Sigma Z adjusted for site specific surface roughness of 100 cm using 3 cm as basis • Sigma Y adjusted for plume meander (3 minute and 20 minute releases) using 3 minute time basis

  9. Baseline for MACCS2 Calculations Conditions and parameters used in existing analysis • Source term assumes 100% instant conversion from elemental tritium to tritium oxide • ICRP72 IDCF for elemental tritium – 1.8E-15 Sv/Bq • ICRP72 IDCF for tritium oxide - 1.8E-11 Sv/Bq • Oxide IDCF adjusted by 1.5x accounting for skin adsorption ( = 2.7E-11 Sv/Bq)

  10. Tritium in Several Forms ICRP72 IDCF Values for various forms of Tritium • Organically Bound Tritium – 4.1E-11 Sv/Bq • Elemental Hydrogen – 1.8E-15 Sv/Bq • Tritiated Methane – 1.8E-13 Sv/Bq • Tritiated Water (Oxide) – 1.8E-11 Sv/Bq • Tritiated Water (1.5x Oxide) – 2.7E-11 Sv/Bq • Type F Tritium Compounds – 6.2E-12 Sv/Bq * • Type M Tritium Compounds – 4.5E-11 Sv/Bq * • Type S Tritium Compounds – 2.6E-10 Sv/Bq * *1u AMAD- Influenced by particle size distribution

  11. Methodology Establish baseline parameters and results

  12. Baseline for MACCS2 Calculations Baseline result is 3.25E-10 Sv/Ci tritium oxide • Dry deposition 0.5 cm/sec deposition velocity • 20 minute release duration – 180 second time basis • 100 cm surface roughness – 3 cm basis • Tadmor-Gur far field dispersion coefficients • Ground level (0 meter) release • 11.5 km offsite receptor • 1.5x ICRP72 IDCF (2.7E-11 Sv/Bq) • 1E-04 m-1 Resuspension Coefficient • 95th Dose Quantile

  13. Methodology Vary parameters to determine impact on results

  14. Sensitivity to Dry Deposition Velocity • Plume depleted as it travels downwind • Larger effect as distance from source increases • Base case has 11.5 km offsite receptor

  15. Sensitivity to Dry Deposition Velocity • MACCS2 Results for Sensitivity to various deposition velocity values • All other baseline inputs held constant • One Curie (3.7E+10 Bq) release • 2001 met data only

  16. Sensitivity to Time Basis Adjustment • Plume meander increases dispersion • Adjustment to Sigma Y based on power law • 180 seconds for prairie grass experiments specified in MACCS2 FGR • Time basis 600 seconds • Time basis equal to release duration (1200 seconds)

  17. Sensitivity to Time Basis Adjustment • MACCS2 Results for Sensitivity to various Time Basis Adjustment values • 20 minute release duration • All other baseline inputs held constant • One Curie (3.7E+10 Bq) release • 2001 met data only

  18. Sensitivity to Surface Roughness Adjustment • Vertical turbulence increases dispersion • Adjustment to Sigma Z based on power law • 3 cm for prairie grass experiments

  19. Sensitivity to Surface Roughness Adjustment • MACCS2 Results for Sensitivity to various surface roughness values • 3 cm basis • All other baseline inputs held constant • One Curie (3.7E+10 Bq) release • 2001 met data only

  20. Sensitivity to Resuspension • Depletion of the plume results in a ground concentration (Bq/m2) • Wind and traffic suspend deposited activity back into atmosphere • Resuspension Concentration Coefficient of 1E-04 is default value in MACCS2 FGR – Baseline Input • EARLY module input • CHRONC module calculates environmental collective population doses using 1E-05 after emergency response phase • 2007 paper by O’Kula and Thoman

  21. Sensitivity to Resuspension • MACCS2 Results for Sensitivity to various Resuspension Coefficients • All other baseline inputs held constant • One Curie (3.7E+10 Bq) release • 2001 met data only • 0.5 cm/sec dry deposition may influence magnitude

  22. Sensitivity to Dispersion Coefficients • Typically not practical to get site specific data (budget, schedule, technical hurdles, etc.) • Choices of default dispersion coefficients • Selection based on applicability to conditions (surface roughness, elevation, terrain, distance, time of release, etc.)

  23. Sensitivity to Dispersion Coefficients Default Sets of Dispersion Coefficients • Tadmor-Gur widely used for ground releases • Briggs typically used for elevated releases • Pasquill-Gifford discussed in MACCS2 documentation (T-G is an implementation of P-G) • Julich developed in Germany for elevated release from very tall stack

  24. Sensitivity to Dispersion Coefficients Software Quality Assurance Issues • HSS 2009-05 error in MACSS2 v1.13.1 and v2.4 • Error dependent on input form of dispersion coefficients • Other errors reported for “new” plume meander model • The results for the next slide generated using MACCS2 v2.5; all previous results based on “Toolbox” v1.13.1

  25. Sensitivity to Dispersion Coefficients • MACCS2 Results for Sensitivity to various dispersion coefficients • All other baseline inputs held constant - issues • 0 meter ground release • Sigma Z surface roughness adjustment to 100 cm from 3 cm basis • Sigma Y time basis adjustment • Distance to receptor

  26. Conclusion • The comparisons applicable only to facility where tritium is dominant release • Acute accident releases - Ground level only • Offsite receptor @ 11.5 km

  27. Conclusion • Tadmor-Gur dispersion coefficients appear to be a reasonable choice for ground level releases • All three evaluated dispersion coefficients gave roughly comparable results for 11.5 km receptor

  28. Conclusion • Changing the deposition velocity parameter from 0.5 to 0 cm/sec may increase the offsite dose to this receptor by about 17%

  29. Conclusion • Changes to other parameters besides deposition velocity might have an even larger impact on offsite dose

  30. Conclusion • Potential future technologies emphasizing tritium compounds may be impacted by filtered and unfiltered release parameters • Unlike current source term assumption of 100% instant conversion to oxide • Needed research publications into response of tritium compounds under thermal stress

  31. References • 2010, EFCOG SAWG Presentation by Kevin Brotherton, “Significant Sensitivities in Developing Radiological Dose Consequences When Using MACCS2” • 2007, Paper by O’Kula & Thoman, WSRC-STI-2007-00027, “Modeling Atmospheric Releases of Tritium from Nuclear Installations” • 2004, MACCS2 Computer Code Application Guidance for Documented Safety Analysis, DOE-EH-4.2.1.4-MACCS2-Code Guidance (MACCS2 FGR) • 1998, Code Manual for MACCS2: Volume 1, User’s Guide, NUREG/CR-6613 • 2001, ICRP Database of Dose Coefficients & ICRP 72

  32. Questions

More Related