Geochemical Modeling of Radionuclide Mobility in Natural ...time; NpO 2 (s) will oxidize to soluble...
Transcript of Geochemical Modeling of Radionuclide Mobility in Natural ...time; NpO 2 (s) will oxidize to soluble...
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)
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1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01
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rom
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t ce
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urc
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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
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[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
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1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01
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seg
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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
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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
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seg
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nte
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urc
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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
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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
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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