Particle Size Distribution and Deposition Velocity Investigations at WTP

1. Particle Size Distribution and Deposition Velocity Investigations at WTP Jorge Schulz jschulz@bechtel.com Bechtel National Inc. 10 May 2012

2. Introduction • Background leading to the deposition velocity investigation • Particle size distributions investigated • Determination of deposition velocity distributions • Calculation of atmospheric dispersion factors • Effects of WPT processes on particle size distributions • Conclusions

3. What is deposition velocity? • Dry deposition velocity (Vdd) is an empirical function of: • Particle size distribution • Wind speed • Surface roughness • Atmospheric stability class • Vdd is used to account for plume depletion as plume travels downwind

4. Background • At WTP initially a value of 1 cm·s-1 for Vdd was used for unmitigated releases • Based on DOE guidance for MACCS2 • DOE-STD-1189-2008 Appendix A • Subsequently the Defense Nuclear Facility Safety Board (DNFSB) concluded that 0.1 cm·s-1 for Vdd was appropriate • Based on an average particle size of 2 μm • Responding to the DNFSB, DOE recommended a value of 0.3 cm·s-1 for Vdd

5. Investigation at WTP • Due to the differing opinions of DOE and the DNFSB, WTP launched an investigation to: • Obtain particle sized distributions (PSD) for the incoming waste from Tank Farms • Develop Vdd distributions • Determine depleted atmospheric dispersion factors (χ/Q) based on the incoming waste PSDs • Determine a single value that results in a 95th percentile depleted χ/Q • Investigate the effects of particle densities and respirable fractions on the depleted χ/Q

6. Sources of Data • WTP-RPT-153 • Extensive Review of Hanford waste PSDs • Composite PSDs developed representing waste in 19 Hanford Tanks • WTP-RPT-048 • Ongoing investigation of waste form qualification for tank 241-AZ-101 • BNFL-RPT-038 • Investigated the effects of caustic leaching and/or water washing waste before vitrification • Data for tanks AZ-101 and AZ-102 from Tank Waste Information Network System (TWINS)

7. Particle Size Distributions

8. Particle Size Distributions

9. Particle Size Distributions - Respirable

10. Particle Size Distributions - Respirable

11. What’s Next? • PSDs are very spread out – little consistency between sources • A Monte Carlo simulation was created • Vdd distributions developed • Resultant χ/Q distributions developed

12. Monte Carlo Simulation • Spreadsheet based on Regulatory Guide 1.145 Gaussian Model • 10 years of meteorological data • Uses particle size distributions previously determined

13. Vdd Cumulative Distribution

14. Vdd Results and Observations • Deposition velocities from 0.1 to 1,500 cm·s-1 • Mean from 0.65 to 61 cm·s-1 • Particles with Vdd greater than a few cm·s-1 are not in the respirable range • Further investigation on respirable range (<10 μm AED)

15. Vdd Cumulative Distribution - Respirable

16. 95th Percentile χ/Q and Resultant Vdd • Using the respirable fraction PSDs, the 95th percentile χ/Q was determined • The single-value Vdd that would result in the 95th percentile χ/Q was back-calculated • Vdd is in the range of 0.32 to 0.47 cm·s-1

17. Depleted χ/Q Distribution - Respirable

18. Depleted χ/Q Distribution - Respirable

19. Effects of WTP Processing on PSDs and χ/Qs • WTP pretreatment of Tank Farm waste includes: • Ultrafiltration • Dilute caustic washing • Elevated temperature caustic leaching • Thus pretreatment of the waste changes the PSDs • Mean particle diameter decreases from 3.8 to 1.2 μm during pretreatment operations • Vdd that yields the 95th percentile χ/Q is in the range of 0.29 to 0.40 cm·s-1

20. Conclusions • Full range PSDs as reported have large variations • Limiting PSDs to the respirable range (<10 μm AED) indicates that the Vdd and χ/Qs are not very sensitive to differences • A Vdd of 0.3 cm·s-1 is reasonable from the work performed • Conservatively, WTP selected a Vdd of 0.1 cm·s-1 for unmitigated releases and 0.0 cm·s-1 for mitigated releases (HEPA filtered)