Particle Size Distribution and Deposition Velocity

Investigations at WTPJorge Schulz

jschulz@bechtel.comBechtel 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 TWINSMean (μm) 11 10 125 6.2 38 335 Percentile (μm) 0.69 0.69 3.7 0.5 2.4 1.4Median (μm) 4.1 4.1 37 4.0 7.2 6.395 Percentile (μm) 32 32 555 20 187 164Respirable 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

Frac

tion

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 TWINSMean (μm) 3.1 1.7 5.8 3.5 4.6 4.05 Percentile (μm) 0.69 0.53 1.6 0.5 1.9 1.2Median (μm) 2.5 1.5 5.5 3.0 4.8 4.295 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

Frac

tion

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

Frac

tion

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

Frac

tion

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

Frac

tion

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

Frac

tion

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