Geochemical Modeling of Radionuclide Mobility in

Natural and Engineered Systems

Brian A. Powell*,†, Abdullah Al Mamun*, Nathan Conroy*, Mine Dogan*, Melody

Maloubier*, Kathryn Peruski*, Stephen Moysey*, Timothy A. DeVol*, Hilary

Emerson, Daniel I. Kaplan†, Mavrik Zavarin#, Annie Kersting#

*Clemson University Florida International University

†Savannah River National Laboratory#Lawrence Livermore National Laboratory

Interagency Steering Committee on Performance and Risk Assessment

Community of Practice (P&RA CoP) Annual Technical Exchange Meeting

Theme: Risk-Informed Approach for Defining End State for Closure of Remediated

Sites

October 30 –November 1, 2018

Savannah River National Laboratory

• Chemical and physical transformations of solid

Np(IV), Np(V), Pu(IV), and Pu(V) sources exposed to

natural conditions

– Utilizing RadFLEx (Radiological Field Lysimeter

Experiment) at SRS

– Comparison with mini-lysimeter experiments from 1980’s

• Real time monitoring of Tc transport through

heterogeneous redox environments

Presentation overview

Field lysimeter facilities

• Field lysimeter:

essentially a large

soil column left

exposed to

natural

environmental

conditions

RadFLEx (SRS) RadFATE (Clemson)

Lysimeter source materials

PuO2 source (left) and autoradiography image (right)

Lysimeter destructive sampling

Pu(V)-NOM

Lysimeter

Pu(V)

Lysimeter

• Deploy Pu and Np sources in a variety of different

initial forms, including soil amendments with organic

matter

– Complimentary comparison of Np(VI)/Pu(IV) and

Np(V)/Pu(V) sources

• Lysimeters deployed in triplicate to allow sampling at

multiple times, to date lysimeters after 2-5 years have

been recovered and analyzed

• Pre and post-experimental observations of solid phase

transformations using SEM/TEM, XAS, and batch

desorption

Experimental approach

Lysimeter Source Materials

• Materials synthesized and

characterized at SRNL ▪ Pu(V)O2NH4(CO3) (6)*

▪ Pu(III)2(C2O4)3 (3)

▪ Pu(IV)(C2O4)2 (6)**

▪ Pu(IV)O2-colloids (3)

▪ Np(V)NO3 (2)

▪ Np(IV)O2 (2)

– * Three sources were amended with natural

organic matter to examine reducing ability and the

effect on Pu mobility

– ** Grass was added to three lysimeters to see

effect of vegetation on mobility

• ⁓ 2-10 mg of solid

• A set of sources were kept in an

inert atmosphere as references

2 978 kBq 239Pu

760 kBq 240Pu

26 427 kBq 241Pu

Roberts et al., SRNL-STI-2012-00603, 2012.

Effluent and Soil SamplesOn Site

• Quarterly sampling

• Monthly monitoring

Laboratory measurements

• pH and dissolved oxygen (DO)

measurements

• Effluent collection bottles

acidified to 2% HNO3

Analytical Techniques

• Direct effluent and acid digested

soil analysis for Pu and Np

• Inductively coupled plasma

mass spectrometry

(ICP-MS)

• Gamma spectroscopy using a

high purity germanium detector

(HPGe)

• Liquid Scintillation Counting

(LSC) using a Hidex 300SL

• Chemical and physical transformations of solid

Np(IV), Np(V), Pu(IV), and Pu(V) sources

exposed to natural conditions

• Peruski, K., Maloubier, M., Kaplan, D.I., Almond, P.M. and

Powell, B.A., “Mobility of aqueous and colloidal neptunium

species in field lysimeter experiments,” Environmental Science and

Technology, 52(4), 1963-1970, 2018.

Working hypothesis:

1. All Pu sources will convert to a PuO2+x(s) phase over

time; NpO2(s) will oxidize to soluble NpO2+

2. Dissolution of polycrystalline phases occurs via

alteration of phases along grain boundaries and formation

of mobile colloids or polynuclear aqueous species

Influence of Redox Cycling and PuO2 Dissolution

Batuk et al., Multiscale Speciation of U

and Pu at Chernobyl, Hanford, Los

Alamos, McGuire AFB, Mayak, and Rocky

Flats, Environ. Sci. Technol., 2015, 49

(11), pp 6474–6484

Model of PuO2 dissolution by Neck et al. (2007)

Neck et al., Radiochim. Acta 95, 193–207 (2007)

-2

0

2

4

6

8

10

12

14

16

18

20

1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01

Dis

tan

ce f

rom

seg

men

t ce

nte

r to

so

urc

e (c

m)

[Pu]soil / [Pu]soil@source

L41 NH4Pu(V)O2CO3 L21 NH4Pu(V)O2CO3 +OM

Pu soil concentration profiles

Source

Pu(V) sources: Maloubier et al., in preparation, 2018

-2

0

2

4

6

8

10

12

14

16

18

20

1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01

Dis

tan

ce f

rom

seg

men

t ce

nte

r to

so

urc

e (c

m)

[Pu]soil / [Pu]soil@source

L41 NH4Pu(V)O2CO3 L21 NH4Pu(V)O2CO3 +OM

Pu soil concentration profiles

Source

Pu(V) sources: Maloubier et al., in preparation, 2018

Things I would like

you to remember:

Pu transport from

NH4PuO2CO3 + OM

retarded relative to

OM free lysimeter

-2

0

2

4

6

8

10

12

14

16

18

20

1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01

Dis

tan

ce f

rom

seg

men

t ce

nte

r to

so

urc

e (c

m)

[Pu]soil / [Pu]soil@source

L41 NH4Pu(V)O2CO3 L21 NH4Pu(V)O2CO3 +OM Pu(VI)O2(NO3)2

Pu soil concentration profiles

Pu(VI)O2(NO3)2(s): Kaplan, D. I et al., Environ. Sci. Technol. 2006, 40, (2), 443-448.

Pu(V) sources: Maloubier et al., in preparation, 2018

Things I would like

you to remember:

Pu transport from

NH4Pu(V)O2CO3 +

OM retarded relative

to OM free lysimeter

Pu transport from

Pu(VI) source (1980s)

was further than both

NH4Pu(V)O2CO3

sources

Source

-2

0

2

4

6

8

10

12

14

16

18

20

1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01

Dis

tan

ce f

rom

seg

men

t ce

nte

r to

so

urc

e (c

m)

[Pu]soil / [Pu]soil@source

L41 NH4Pu(V)O2CO3 L21 NH4Pu(V)O2CO3 +OM

Pu(VI)O2(NO3)2 Pu(IV)(NO3)4

Pu soil concentration profiles

Pu(VI)O2(NO3)2 and Pu(NO3)4: Kaplan, D. I et al., Environ. Sci. Technol. 2006, 40, (2), 443-448.

Pu(V) sources: Maloubier et al., in preparation, 2018

Things I would like

you to remember:

Pu transport from

NH4Pu(V)O2CO3 +

OM retarded relative

to OM free lysimeter

Pu transport from

Pu(VI) source (1980s)

was further than both

NH4Pu(V)O2CO3

sources

Pu transport from

NH4Pu(V)O2CO3 +

OM source was most

comparable to

Pu(IV)(NO3)4 (1980s)

Source

Speciation changes in the sources (XANES)

Archived source analyzed 3 years after the synthesis :

No pure Pu(V)

Mixture of Pu(V) and Pu(IV) confirmed by solvent

extraction and linear combination fit

18040 18060 18080 18100 18120

fit

experimental

No

rma

lize

d A

bso

rba

nce

Energy (eV)

65% PuO2, 35% Pu(V)

Sources Pu(IV) Pu(V)

NH4PuO2CO3 archived 65 % 35 %

NH4PuO2CO3 from

lysimeter

93 % 7%

NH4PuO2CO3 from

lysimeter with OM

85 % 15 %

0 2 4 6 8 10 12

NH4PuO

2CO

3 source/OM; 3 yr in lys.

NH4PuO

2CO

3 source; 3 yr in lys.

EX

AF

S a

mp

litu

de

in

k2.

(k)

Wave number k (Å-1)

0 2 4 6

NH4PuO

2CO

3 source/OM; 3 yr in lys.

FT

am

plit

ud

e k

2.

(k)

Non phase shift corrected distance(Å)

NH4PuO

2CO

3 source; 3 yr in lys.

1

Speciation changes in the sources (EXAFS)

8 Pu-O at 2.30(1) Å, σ2=0.012 Å2

3.9 Pu-Pu at 3.79(1) Å, σ2=0.0033 Å2

S02 = 1.0, e0 = -3.29 eV, R-factor = 0.9%

8 Pu-O at 2.33(1) Å, σ2=0.012 Å2

4.5 Pu-Pu at 3.82(1) Å, σ2=0.0043 Å2

S02 = 1.0, e0 = -3.29 eV, R-factor = 1.6%

PuO2 Crystal structure

8 Pu-O at 2.337 Å

12 Pu-Pu at 3.816 Å

24 Pu-O at 4.474 Å

(I)

(II)

(I) (II)

Conradson, S. D.; et al., J. Am. Chem. Soc. 2004, 126, 13443-13458.

• Similar FT indicating all sources exposed in field lysimeters became disordered

PuO2+x-y(OH)2y.zH2O*

*Conradson, S. D.; et al., J. Am. Chem. Soc. 2004, 126, 13443-13458.

EXAFS comparison of all Pu sources

Effluent analysis of Pu source lysimeters

Lysimeter

Sampling Date –

March 2015

Measured Pu (M)

Sampling Date -

Oct-Dec 2015

Measured Pu (M)

Sampling Date –

March 2016

Measured Pu (M)

Pu(IV)(C2O4)2 8 ± 1 x 10-15 < 5 x 10-15 < 5 x 10-15

Pu(III)2(C2O4)3 9 ± 2 x 10-13 < 1.1 x 10-14

Pu(III)2(C2O4)3 8.6 ± 1.0 x 10-15

Pu(IV)(C2O4)2 3.8 ± 0.5 x 10-13

Pu(IV)O2 2.6 x ± 0.4 x 10-14 1.6 x 0.2 x 10-14

Pu(IV)O2 9 ± 2 x 10-13

239/240Pu Analysis via coprecipitation, ion exchange separation, and alpha spectroscopy

Breakthrough of 237Np from Np(V) source Lysimeters

• Sources:

– Np(IV)O2 (31, 32)

– Np(V)nitrate (29, 30)

• +IV, +V, and +VI dominate in

terrestrial environments

• Soluble Np(V)O2+ is mobile at

relevant pH values

• Np(IV) is more common

under reducing conditions

– less soluble than NpO2+

– higher tendency to sorb to

solid surfaces and form

aqueous complexesLysimeter

Initial Activity

in source (uCi)

Cumulative

activity in

effluent

Fraction of total

activity in

effluent

29 1.24 0.05 0.03

30 1.24 0.34 0.27

0

2000

4000

6000

8000

10000

12000

14000

0 5000 10000 15000 20000C

um

mu

lati

ve

Acti

vit

y i

n t

he

Eff

leu

nt

(Bq

)Cumulative Volume Collected (mL)

Lys 29 Lys 30

• Sources:

– Np(IV)O2 (31, 32)

– Np(V)nitrate (29, 30)

• +IV, +V, and +VI dominate in

terrestrial environments

• Soluble Np(V)O2+ is mobile at

relevant pH values

• Np(IV) is more common

under reducing conditions

– less soluble than NpO2+

– higher tendency to sorb to

solid surfaces and form

aqueous complexesLysimeter

Initial Activity

in source (uCi)

Cumulative

activity in

effluent

Fraction of total

activity in

effluent

29 1.24 0.05 0.03

30 1.24 0.34 0.27

1.0E-12

1.0E-11

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

0 5000 10000 15000 20000 25000

Aq

ue

ou

s N

p C

on

ce

ntr

ati

on

(m

ol/

L)

Cumulative Volume Collected (mL)

Lys 29

Lys 30

Lys 32

Breakthrough of 237Np from Np(V) source Lysimeters

Solid phase analysis of lysimeters containing

Np(IV) and Np(V) sources

-33

-30

-27

-24

-21

-18

-15

-12

-9

-6

-3

0

3

6

9

12

15

18

21

24

27

0.001 0.01 0.1 1 10

Dis

tance f

rom

Sourc

e(c

m)

Concentration of Np-237 in soil (Bq/g)

Np(IV) Source

MDC

Np(V) Source

Source

1.0E+00

1.0E+01

1.0E+02

1.0E+03

1.0E+04

0.5 cm

below

source

2.5 cm

below

source

15 cm

below

source

5 cm

above

source

15 cm

below

source

25 cm

below

source

Kd

(m

L/g

)

Np(IV) Lysimeter

Np(V) Lysimeter

𝐾𝑑 =[𝑁𝑝]𝑠𝑜𝑙𝑖𝑑[𝑁𝑝]𝑎𝑞𝑢

Higher Kd values for Np near the NpO2 source

indicate the presence of a less mobile species

• Field lysimeter experiments have noted marked

differences in NpO2(s) and NpO2NO3(s) sources.

• Potential rate limiting steps of surface oxidation examined

in sources and controlled laboratory testing (future work)

• EXAFS analysis of Np(IV) source indicates significant

disorder from NpO2

NpO2 Oxidative Dissolution Under Field Conditions

Original source NpO2(s)

NpO2(s) after 4y in field lysimeter

Peruski et al., Environmental Science and Technology, 2018, 52(4), 1963-1970

• Field lysimeter experiments have noted marked

differences in NpO2(s) and NpO2NO3(s) sources.

• Potential rate limiting steps of surface oxidation examined

in sources and controlled laboratory testing (future work)

• EXAFS analysis of Np(IV) source indicates significant

disorder from NpO2

NpO2 Oxidative Dissolution Under Field Conditions

Original source NpO2(s)

NpO2(s) after 4y in field lysimeter

Peruski et al., Environmental Science and Technology, 2018, 52(4), 1963-1970

• Field lysimeter experiments have noted marked

differences in NpO2(s) and NpO2NO3(s) sources.

• Potential rate limiting steps of surface oxidation examined

in sources and controlled laboratory testing (future work)

• EXAFS analysis of Np(IV) source indicates significant

disorder from NpO2

NpO2 Oxidative Dissolution Under Field Conditions

Original source NpO2(s)

NpO2(s) after 4y in field lysimeterAutoradiography of soil below NpO2 lysimeter source

Peruski et al., Environmental Science and Technology, 2018, 52(4), 1963-1970

Successive Autoradiography

Removed circled area of

sediment onto new

autoradiography plate to isolate

area of highest activity

Ultimate goal would be to

reduced sediment to single

grains that could be

mounted on an SEM stub

for analysis27

New Lysimeter NpO2(s) Source Analysis

New NpO2(s) sources buried in

RadFATE faciltity at three locations

within the lysimeter

Cubic crystals have surface alteration

(small granules on the surface)28

Conceptual model of Np transport

Np(IV) Source

Dissolved NpO2+

Colloidal Np

Oxygenated Rainwater

Oxidation

Np(V) Source

Dissolved NpO2+

Oxygenated Rainwater

4D SPECT/CT and 1D Gamma Scanning

imaging of flow and reactivity in porous media

• Dogan, M., Moysey, S.M., Ramakers, R. M., DeVol, T. A., Beekman, F. J.,

Grown, H. C., Powell, B. A., “High-resolution 4D pre-clinical SPECT/CT

imaging of technetium transport within a heterogeneous porous media,”

Environmental Science and Technology, 51, 2864–2870, 2017. (DOI:

10.1021/acs.est.6b04172)

• Highlighted by DOE Office of Science

– https://science.energy.gov/bes/highlights/2017/bes-2017-11-d/

Capillary tubes(ID=1.1mm, OD=1.5mm)

Goal:

Evaluate capabilities of

SPECT for 4D imaging

of transport phenomena.

SPECT/CT Imaging of Porous Media

filter paper

Optical image of the column packed for the experiment.

High-resolution CT data rendered for the volume representation.

X-Ray Computed Tomography (CT) Imaging

silica flour 0.25 mm 0.5 mm soil 1 mm 2 mm 3 mm 4 mm

Unique object detection to about 200mm

X-Ray Computed Tomography (CT) Imaging

SPECT Imaging Study

Injection:NaCl + 3.12 MBq/ml of 99mTcO4

- @ 1.5 mL/min

SPECT Imaging Protocol:Static: pump stopped every 20min (10min detection time)Time-lapse: continuous while pump on (2 or 5min detection time)Decay: activity monitored with pump off for 36hrs (2hr detection time)

flow direction

Comparison of Structure and 99mTc Activity

Norm.

Activity

1

6

5

8 4

3

1 7

2

6

5

8 4

3

1 7

2

(1) Filter paperGrains (low activity): (2) 4mm grain

(3) 2mm grainPores (high activity): (4) Large pore

(7,8) Capillary tubesAnomalous: (5) High activity

(6) Low activityUnique object detection to about 2mm.

Time-lapse Imaging of 99mTc Activity

A

B

E

D

C

Time-lapse Imaging of 99mTc Activity

(A) Low flow zone

(B) Preferential flow

(C) Preferential flow (gravity driven?)

(D) Non-uniform flow

(E) Filter papers

High activity from sorption?

Time-lapse Imaging of 99mTc Activity99mTc Breakthrough Curves

@ 60 mm @ 110 mm

3D view of the 99mTc saturated media

• A tracer experiment was conducted and SPECT images were collected throughout the transport experiment.

• Technetium-99m sorption was observed under anoxic conditions.• Sorption capacities of three cylinders were significantly different.

• TiO2 is the highest (?)• Silica flour is the lowest (?)

• It is possible to extract quantitative information related to sorption/release mechanisms by using this kind of a column and pulse tracer tests.

Experimental column was packed under anoxic conditions with SRS soil 3 identical cylinders amended with (8wt%) silica flour (0-60 µm), (8wt%) anatase (TiO2), and (8wt%) titanium substituted magnetite and 1 layer amended with (8wt%) titanium substituted magnetite

Orthogonal slices showing amended soil cylinders and layer.

Frozen soil cylinder.

Imaging 99mTc Transport through Heterogeneously Reducing Porous Media

RATIONALE: The intent of this experiment is to: (1) test the efficiency of the SPECT system for analyzing radionuclide migration in the Savannah River Site (SRS) soil and titanium-substituted magnetite nanoparticles, and (2) monitor the in situ sorption of technetium-99m in soils and nanoparticles and relate this to soil structure and nanoparticle concentration.

Schematic showing the column design and dimensions.

Imaging 99mTc Transport through Heterogeneously Reducing Porous Media

-15

-10

-5

0

5

10

15

20

1 10 100 1000

Dis

tan

ce from

sou

rce (in

)

Activty per unit mass of soil (Bq/g)

Lysimeter 20

Lysimeter 8

MinimumDetectableConcentration

99Tc Soil Profile Distribution

• Triplicate samples were prepared

– Error is σ of measurements

• Collection time for lysimeter 8 was

2 months greater than lysimeter 20

• Total Activity Measured in soil:

– Lysimeter 8: 34.1 µCi

– Lysimeter 20: 99.1 µCi

31.7 %

62.1 %

35.1 %

65.0 %

2.6% 3.3 %

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

7 8 19 20

Cu

mu

lati

ve

fracti

on

of

init

ial

Tc

measu

red i

n e

fflu

en

t

Lysimeter number

FY13Q2b

FY13Q2a

FY13Q1

FY12Q4

• Notable spectral features

(arrows)

– TcO4- pre-edge feature

– White line splitting in

TcO2(s)

– Broad post-edge feature in

TcSx (Tc2S7)

• Using the reductive

elimination method,

proposed progression of

Tc speciation follows a

hydrolysis species

(Tc(IV)O(OH)2(H2O)3)

followed by partially then

fully sulfidized species.

Tc XAS Analysis

21000 21040 21080 21120 21160 21200

27D H2O

2 (0-10mm)

27D (334d) (0-10mm)

27C (281d) (11-15mm)

27C (281d) (0-6mm)

27B (117d) (15-17mm)

27B (117d) (0-8mm)

27E (453d) (0-3mm)

27E (453d) (3-7mm)

27E (453d) (7-9mm)

27E (453d) (12.5-16mm)

27E (453d) (16-19mm)

27E (453d) (19-21mm)

Tc2S

7(s)

Tc(IV)O2(am)

Tc(VII)O4

-(aq)

Norm

aliz

ed Inte

nsi

ty

Energy (eV)

Arai, Y., et al., Journal of Hazardous Materials, 342, 510-518, 2017.

Modeling Tc release from cementitious waste forms in

RadFLEx field lysimeters

• NpO2 source oxidation causes 1) significant disorder in the

NpO2 structure and 2) enhanced downward migration in field

lysimeters

– Appears to be influenced by colloidal transport

• Pu-oxalate and Pu-ammonium carbonate sources alter to a PuO2

type structure, rate enhanced by exposure to field conditions

• Downward migration appears to be impacted by colloidal

transport

– Potential change in conceptual model of Pu dissolution where

disaggregation of polycrystalline bulk materials creates colloids

• Migration of Tc approximated assuming leaching from reducing

grout source (using literature values) and dynamic flow

conditions

Summary

Acknowledgements

DOE EPSCoR Grant: This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Basic Energy Sciences and Office of Biological and Environmental Research under Award Number DE-SC-00012530

SRNL Joint Appointment: Support of Laboratory Research and Development

Lysimeter effluent analysis and Pu soil analysis is based upon work supported

by Savannah River Remediation under project SRRA021685SR.

• Faculty: Stephen Moysey, Larry Murdoch, Tim DeVol, Nishanth Tharayil, Nicole Martinez

• Postdocs: Mine Dogan, Vijay Santikari• Students: Kyle Barber, Bryan Erdmann, Rebecca Dozier, Dawn

Montgomery, Nimisha Edayilam, Brennan Ferguson, Kathryn Peruski, Abdullah Al Mamun