Particle Size Distribution and Deposition Velocity Investigations at WTP
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Transcript of Particle Size Distribution and Deposition Velocity Investigations at WTP
Particle Size Distribution and Deposition Velocity
Investigations at WTPJorge Schulz
[email protected] 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
Introduction
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
What is deposition velocity?
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
Background
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
Investigation at WTP
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)
Sources of Data
Particle Size Distributions
ParameterComposit
e PuO2
AZ-101 AZ-101
AZ-102 No
Sonication
AZ-102 Sonicatio
n
Source WTP-RPT-153 TWINS WTP-RPT-048 TWINS
Mean (μm) 11 10 125 6.2 38 33
5 Percentile (μm) 0.69 0.69 3.7 0.5 2.4 1.4
Median (μm) 4.1 4.1 37 4.0 7.2 6.3
95 Percentile (μm) 32 32 555 20 187 164
Respirable Fraction 69% 45% 23% 84% 52% 57%
Particle Size Distributions
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.1 1 10 100 1000
Cum
ulat
ive
Fra
ctio
n
Particle Size (mm)
AZ-101 TWINS
AZ-101 WTP-RPT-048
AZ-102 no Sonication
AZ-102 Sonication
Composite
PuO2
Particle Size Distributions - Respirable
ParameterComposit
e PuO2
AZ-101 AZ-101
AZ-102 No
Sonication
AZ-102 Sonicatio
n
Source WTP-RPT-153 TWINS WTP-RPT-048 TWINS
Mean (μm) 3.1 1.7 5.8 3.5 4.6 4.0
5 Percentile (μm) 0.69 0.53 1.6 0.5 1.9 1.2
Median (μm) 2.5 1.5 5.5 3.0 4.8 4.2
95 Percentile (μm) 6.9 3.6 9.5 9.0 7.2 7.2
Particle Size Distributions - Respirable
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.1 1 10
Cum
ulat
ive
Fra
ctio
n
Particle Size (mm)
AZ-101 TWINS
AZ-101 WTP-RPT-048
AZ-102 no Sonication
AZ-102 Sonication
Composite
PuO2
PSDs are very spread out – little consistency between sources
A Monte Carlo simulation was created◦ Vdd distributions developed◦ Resultant χ/Q distributions developed
What’s Next?
Spreadsheet based on Regulatory Guide 1.145 Gaussian Model
10 years of meteorological data Uses particle size distributions previously
determined
Monte Carlo Simulation
Vdd Cumulative Distribution
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03
Cum
ulat
ive
Fra
ctio
n
Deposition Velocity(cm . s-1)
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)
Vdd Results and Observations
Vdd Cumulative Distribution - Respirable
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.0E-01 1.0E+00 1.0E+01
Cum
ulat
ive
Fra
ctio
n
Deposition Velocity(cm . s-1)
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
95th Percentile χ/Q and Resultant Vdd
Depleted χ/Q Distribution - Respirable
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.00E-10 1.00E-09 1.00E-08 1.00E-07 1.00E-06 1.00E-05 1.00E-04
Cum
ulat
ive
Fra
ctio
n
c/Q (s . m-3)
Depleted χ/Q Distribution - Respirable
0.8
0.85
0.9
0.95
1
1.0E-06 1.0E-05 1.0E-04
Cum
ulat
ive
Fra
ctio
n
c/Q (s . m-3)
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
Effects of WTP Processing on PSDs and χ/Qs
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)
Conclusions