Transcript No Slide Title

Isotopic Composition, Speciation and Mobility of actinides in the Groundwater at DOE Savannah River and Hanford
Sites
K.O. Buesseler (1), M.H. Dai(1), J.M. Kelley(2), S. Pike(1), J. Andrews(1), T.C. Maiti(2), and J.F. Wacker(2)
(1) Woods Hole Oceanographic Institution, MS 25, Woods Hole, MA 02543; (2) Pacific Northwest National
PO Boximportant
999, Richland, for
WA 99352
C.Lab,
Issues
accurate
B. Groundwater sampling and
processing Well water
Prior studies have revealed that speciation and/or complexation
chemistry have dramatic effect on the mobility of many elements in
aquifers because sorption onto any solid phase will depend upon
the speciation in solution (Choppin, 1988; Choppin, 1992; Moulin
and Ouzounian, 1992; Marley et al., 1993; Cooper et al., 1995).
Less well understood, is how interactions between source
characteristics (i.e. Pu from fallout, underground test debris, liquid
vs. vitrified waste) and ambient geochemistry and hydrology
interact to change speciation leading to enhanced or retarded
actinide migration in groundwater. Total radionuclide activity data
are not particularly revealing since speciation, not total activity
levels, are needed to predict mobility. Extreme care must be taken
not to alter the ambient geochemistry and colloid abundances
during sampling. Finally, isotopic information is needed to identify
Pu sources which can be linked to the physical-chemical form of Pu
and hence its mobility.
multiprobe (O2,
Unfiltered
pH, turbidity etc.)
0.2 mm
prefiltration
Permeate (<1 kD)
Pu Isotopic
composition
with TIMS
Retentate
On-site
Cross-flow
ultrafiltratio
n
(> 1 kD)
On-site oxidation
state separations
E. Hanford Site
N2 purged and
sealed
Oxidized and reduced
forms
100
Water Retention
Basins K-32A
(atom ratio)
240Pu/239Pu
16.0
12.0
0.4
0.3
0.2
0.1
0.0
Aug. 97
May 98
Filtrate
Perm eate
Colloid al
Unfiltered
8.0
4.0
239
78
103C
108D
92D
78
Well #
79
Pu (atom/kg)
Percent oxidized 240Pu in filtrate (<0.2µm), Permeate
(<1kD) and colloidal (1kD-0.2 µm) size fractions.
0.008
0.006
0.004
K-E reactor (N-reactor signal)
upstream
Global Fallout
K-W reactor
downstream
0.002
241
1e+5
108D103C92D 93D 94C 78 110D 79
Well #
Well #
Unfiltered
Filtrate
Permeate
Colloidal
79
Well #
0.010
110A
27
240Pu
(3a) and 239Pu (3b) atom abundances in filtrate (<0.2µm), Permeate (<1kD) and colloidal
(1kD-0.2 µm) size fractions.
We attribute the highest 240Pu/239Pu ratios to samples that have been impacted by the decay of 244Cm (t½ = 18.1 yrs.) to 240Pu in the seepage basin wastes.
A low 240Pu/239Pu ratio in background well (108D) signifies a source other than global fallout and is most likely due to weapons grade Pu waste of some local
origin.
A low colloidal abundance is consistent with the higher oxidation states, and with overall low natural colloidal organic carbon levels at this site.
For 240Pu, we find that >75-95% of the Pu is in the oxidized form in all of the size classes.
I. Acknowledgments: This work was supported by the Department of Energy under Grant #DOE DE-FG07-96ER14733. We are grateful for the kind assistance
from James Haffener and Keith Johnson from the Savannah River Site and Shannon Goodwin, Evan Dresel, Scott Conley, Teresa Wilson, Debi Morgan, Mike Thomson,
Stuart Luttrel, Loni Peurrung, Dennis Brooks from the Hanford site .
K-West
reactor
32A
2 x 10-4
pCi/l
K-East reactor
106
105
104
Filtrate (<0.2 mm)
Permeate (<1kD)
Colloidal (>1kD)
Total (1997 data)
103
0.05
0.10
0.15
0.20
0.25
Pu/ 239Pu (atom ratio)
0
78
107
1e+6
108D103C92D 93D 94C 78 110D 79
92D
36
Pu is primarily in reduced form near source, with
a trend towards more oxidized forms further
from source
240
1e+5
108D
20
Pu-isotopic composition
0.000
0.00
1e+7
1e+6
Oxidized 240Pu (%)
240
1e+8
1e+7
20
40
0
KE Filter
Plant
KW Reactor
Building
KW Filter
Plant
b.
Pu (atom/kg)
1e+8
40
K-36
Pu (atom/kg)
92D
atom ratio in unfiltered well samples collected in August 1997. b) size fractionated
240Pu/239Pu data from samples collected in May 1998. Note two of the well sites are the same, and that
for well 108D (b), 240Pu/239Pu ratio is only available for an unfiltered sample at this time.
60
60
Well #
240Pu/239Pu
Filtrate
Perm eate
Colloid al
80
KE Reactor
Building
K-106A
a.
80
K-30
K-107A
Well #
100
K-27
K-28
K-109A
Water Retention
Basins
K-110A
108D
a)
% oxidized 239Pu
Columbia
River
239
D. Savannah River Site
In-line
Pu speciation studies
Groundwater sampling
maintain and measure in-situ geochemistry; use low flow sampling to reduce colloid
formation
Cross-flow filtration for separation of colloids
maintain redox state & keep trace metal clean; demonstrate low sorptive losses and
negligible blanks; calibrate CFF with colloid standards
Redox speciation studies
performed immediately in field under nitrogen gas; lanthanium fluoride ppt w/244Pu and
242Pu spikes
Radiochemical purification (WHOI)
careful attention to blanks & yields prior to TIMS
Thermal Ionization Mass Spectrometry (PNNL)
subfemtogram detection limits (10-15 gm or 106 atoms); use 240Pu/239Pu to determine Pu
sources
Pu/ 239Pu (atom ratio)
A. Introduction
The likely source of high 241Pu/239Pu in wells K-109A and
K-27 is N-reactor waste (the K-East reactor basin is
currently being used to store irradiated fuel from the Nreactor).
The isotopic ratio in the other wells reflects the K-reactor
signal, possibly mixed with fallout
106A107A 36 110A 30 109A 28
27 32A
Well #
Pu from Hanford operations found in all groundwater samples from
100K area- low levels (fg/l, 10-4 to 10-6 pCi/l)
Colloidal Pu is minor fraction of total Pu in groundwater-<5-15%
colloidal
G. Summary
Overall, our data suggest that redox speciation can vary considerably at both SRS and HS. Most of the
Pu is in the form <1 kD in size at both sites. The highly varied 240Pu/239Pu ratio can only point to 240Pu
being enhanced downstream due to its production from the more mobile Cm precursor and its own
enhanced mobility in the oxidized form at SRS, and we note that the forms of Pu found at the SRS
would be significantly more mobile than standard models predict. Pu from Hanford operations is
observable from 100K area although the concentration is extremely low.
H. Significance to DOE EMSP
Migration of Plutonium in the Environment is a major problem at several DOE sites, and fundamental data
concerning the interactions between various chemical forms of plutonium with compounds in the environment
are essential to predicting environmental behavior. The results of our research program would: i) provide the
basis for accurate modeling and prediction of actinide transport; ii) allow for remediation strategies to be planned
that might use in-situ manipulations of geochemical variables to enhance (for extraction) or retard (for
immobilization) Pu mobility in the vadose/groundwater zone, and iii) identify specific Pu sources and the extent
of far field, or long-term migration of actinides in groundwaters. This new knowledge is essential to ensure
continued public and worker safety at the DOE sites and the efficient management of cleanup and containment
strategies.