Jorge Schulz Bechtel National Inc. 10 May 2012

 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

 Dry deposition velocity (V dd ) is an empirical function of: ◦ Particle size distribution ◦ Wind speed ◦ Surface roughness ◦ Atmospheric stability class  V dd is used to account for plume depletion as plume travels downwind

 At WTP initially a value of 1 cm·s -1 for V dd was used for unmitigated releases ◦ Based on DOE guidance for MACCS2 ◦ DOE-STD Appendix A  Subsequently the Defense Nuclear Facility Safety Board (DNFSB) concluded that 0.1 cm·s -1 for V dd 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 V dd

 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 V dd distributions ◦ Determine depleted atmospheric dispersion factors (χ/Q) based on the incoming waste PSDs ◦ Determine a single value that results in a 95 th percentile depleted χ/Q ◦ Investigate the effects of particle densities and respirable fractions on the depleted χ/Q

 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)

ParameterCompositePuO 2 AZ- 101 AZ-102 No Sonication AZ-102 Sonication SourceWTP-RPT-153TWINSWTP-RPT-048TWINS Mean (μm) Percentile (μm) Median (μm) Percentile (μm) Respirable Fraction69%45%23%84%52%57%

ParameterCompositePuO 2 AZ- 101 AZ-102 No Sonication AZ-102 Sonication SourceWTP-RPT-153TWINSWTP-RPT-048TWINS Mean (μm) Percentile (μm) Median (μm) Percentile (μm)

 PSDs are very spread out – little consistency between sources  A Monte Carlo simulation was created ◦ V dd distributions developed ◦ Resultant χ/Q distributions developed

 Spreadsheet based on Regulatory Guide Gaussian Model  10 years of meteorological data  Uses particle size distributions previously determined

 Deposition velocities from 0.1 to 1,500 cm·s -1  Mean from 0.65 to 61 cm·s -1  Particles with V dd greater than a few cm·s -1 are not in the respirable range  Further investigation on respirable range (<10 μm AED)

 Using the respirable fraction PSDs, the 95 th percentile χ/Q was determined  The single-value V dd that would result in the 95 th percentile χ/Q was back-calculated  V dd is in the range of 0.32 to 0.47 cm·s -1

 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  V dd that yields the 95 th percentile χ/Q is in the range of 0.29 to 0.40 cm·s -1

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