Single phase melt processed powellite (Ba,Ca)MoO4 for the immobilization of Mo-rich nuclear waste

Article abstract of DOI:10.1016/j.jallcom.2012.09.049

Crystalline and glass composite materials are currently being investigated for the immobilization of combined High Level Waste (HLW) streams resulting from potential commercial fuel reprocessing scenarios. Several of these potential waste streams contain elevated levels of transition metal elements such as molybdenum (Mo). Molybdenum has limited solubility in typical silicate glasses used for nuclear waste immobilization. Under certain chemical and controlled cooling conditions, a powellite (Ba,Ca)MoO₄ crystalline structure can be formed by reaction with alkaline earth elements. In this study, single phase BaMoO₄ and CaMoO₄ were formed from carbonate and oxide precursors demonstrating the viability of Mo incorporation into glass, crystalline or glass composite materials by a melt and crystallization process. X-ray diffraction, photoluminescence, and Raman spectroscopy indicated a long range ordered crystalline structure. In situ electron irradiation studies indicated that both CaMoO₄ and BaMoO₄ powellite phases exhibit radiation stability up to 1000 years at anticipated doses with a crystalline to amorphous transition observed after 1 × 10¹³ Gy. Aqueous durability determined from product consistency tests (PCT) showed low normalized release rates for Ba, Ca, and Mo (<0.05 g/m²).

Full text of DOI:10.1016/j.jallcom.2012.09.049

Journal of Alloys and Compounds 551 (2013) 136–142
Contents lists available at SciVerse ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
Single phase melt processed powellite (Ba,Ca)MoO for the immobilization
4
of Mo-rich nuclear waste
a,
⇑
a
a
a
b
c
Kyle Brinkman , Kevin Fox , James Marra , Jason Reppert , Jarrod Crum , Ming Tang
a
Savannah River National Laboratory, Aiken, SC 29808, USA
Pacific Northwest National Laboratory, Richland, WA 99352, USA
Los Alamos National Laboratory, Los Alamos, NM 87545, USA
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 June 2012
Received in revised form 10 September
Crystalline and glass composite materials are currently being investigated for the immobilization of com-
bined High Level Waste (HLW) streams resulting from potential commercial fuel reprocessing scenarios.
Several of these potential waste streams contain elevated levels of transition metal elements such as
molybdenum (Mo). Molybdenum has limited solubility in typical silicate glasses used for nuclear waste
2
012
Accepted 11 September 2012
Available online 2 October 2012
immobilization. Under certain chemical and controlled cooling conditions, a powellite (Ba,Ca)MoO
talline structure can be formed by reaction with alkaline earth elements. In this study, single phase
BaMoO and CaMoO were formed from carbonate and oxide precursors demonstrating the viability of
4
crys-
4
4
Keywords:
Waste form
Nuclear materials
Radiation damage
Chemical durability
Mo incorporation into glass, crystalline or glass composite materials by a melt and crystallization process.
X-ray diffraction, photoluminescence, and Raman spectroscopy indicated a long range ordered crystalline
structure. In situ electron irradiation studies indicated that both CaMoO
4 4
and BaMoO powellite phases
exhibit radiation stability up to 1000 years at anticipated doses with a crystalline to amorphous transi-
1
3
tion observed after 1 ꢀ 10 Gy. Aqueous durability determined from product consistency tests (PCT)
2
showed low normalized release rates for Ba, Ca, and Mo (<0.05 g/m ).
Ó 2012 Elsevier B.V. All rights reserved.
1
. Introduction
reprocessing [7]. This has led to the development of synthetic rock
or SYNROC as coined by Ringwood et al. in 1979 [8,9]. In addition,
Efforts being conducted by the United States Department of En-
ergy (DOE) under the Fuel Cycle Research and Development
FCR&D) program are aimed at making the U.S. Fuel Cycle more
recent work has been increasingly focused on glass composite
materials (GCM), intermediate between completely amorphous
and fully crystalline materials. In these systems, the crystalline
content and elemental partitioning may be controlled by glass
forming additives and cooling rate [10–12]. Current work is aimed
at developing a high throughput, reliable process for waste form
processing. GCM waste forms may be tailored to the projected
combined fission product waste stream from commercial nuclear
fuel reprocessing where actinides are removed via separations pro-
cesses have the potential to meet the requisite waste loadings, ease
of processing, radiation stability, chemical flexibility, and resis-
tance to aqueous dissolution that are required for long term geo-
logic storage.
(
effective by the development of next generation waste manage-
ment technologies. Some fuel cycles being developed include the
reprocessing of commercial used fuel in the U.S. The envisioned
fuel reprocessing technology would separate the fuel into several
fractions, thus, partitioning the waste into groups with common
chemistry [1]. Immobilization of the High Level Waste (HLW) frac-
tion may be achieved by chemical incorporation into the structure
of a suitable matrix, typically a glass, glass–ceramic composite, or
crystalline ceramic such that it is captured and unable to escape
[
2]. High level waste has been incorporated into borosilicate glass
waste forms at the industrial scale for several decades and is an
established technology [3–6].
Typically, crystalline materials for HLW immobilization have
been densified via hot isostatic pressing [8]. However, recent work
has shown that they can also be produced from a melt process
analogous to GCM processing. For example, demonstrations have
been completed using the Cold Crucible Induction Melter (CCIM)
technology to produce several crystalline ceramic waste forms,
including murataite-rich ceramics [13,14], zirconolite/pyrochlore
ceramics [15], Synroc-C (zirconolite, hollandite, perovskite)
[16,17], aluminotitanate ceramics, and zirconia [18]. This produc-
tion route is advantageous since melters are already in use for
Ceramic (or crystalline) phases incorporate the waste radionuc-
lides as part of their crystal structure. Tailoring of ceramic phases is
based on the knowledge that there are many naturally produced
minerals containing radioactive and non-radioactive species very
similar to the radionuclides of concern in wastes from fuel
⇑
Corresponding author. Tel.: +1 803 725 9843.
E-mail address: kyle.brinkman@srnl.doe.gov (K. Brinkman).
0
925-8388/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jallcom.2012.09.049

K. Brinkman et al. / Journal of Alloys and Compounds 551 (2013) 136–142
137
commercial and defense High Level Waste (HLW) vitrification in
several countries, and melter technology greatly reduces the po-
tential for airborne contamination as compared to processes
involving extensive powder handling operations. Production of
GCM waste forms would be expected to be straightforward using
the CCIM technology and demonstrations to this effect are cur-
rently underway.
(ii) examine the durability of Mo containing powellite phase to
aqueous environments, and (iii) evaluate the radiation stability of
powellite crystalline phases.
2. Experimental
4 4
The materials synthesis focus was to prepare single phase CaMoO and BaMoO
The structure/property relations of individual phases within the
multi-phase assemblage of GCM or ceramic waste forms are partic-
ularly important for the incorporation of challenging elements,
such as molybdenum, which have low solubility in typical HLW
glasses. These elements have concentrations in excess of 13 wt.%
in the projected reprocessing waste streams. GCM waste forms
are advantageous for the immobilization of these species since
they form a stable phase within a glassy matrix [11]. A primary
Mo containing crystalline phase that forms during GCM processing
from a melt process using oxide and carbonate precursors for subsequent structure/
property investigations. Powders of 99.5% pure calcium carbonate (CaCO ), barium
carbonate (BaCO ) and molybdenum oxide (MoO ) from Aldrich (Milwaukee, WI)
3
3
3
were used as precursors for powellite material synthesis. The powders were
weighed in stoichiometric ratios and were ball milled in ethyl alcohol in an alumina
jar with alumina milling media for four hours followed by drying overnight at 70 °C.
Samples of each of the batch materials were melted in an electric resistance heated
furnace to simulate melter production. The blended and dried powders were placed
into Pt/Rh alloy crucibles and melted at 1500 °C for 20 min. Power to the furnace
was then turned off with the crucibles remaining inside to cool slowly (furnace
cooling) to roughly approximate the slow cooling conditions experienced by a
waste form poured from a melter into a canister. The phase development of the
samples prepared from melts was compared with the crystalline phases formed
from powder batches calcined at 900–1100 °C for four hours. Representative sam-
4
has been found to be a (Ba,Ca)MoO powellite phase [5,11]. These
phases have been observed and studied as a component of a mul-
tiphase waste form system. However, little work has been per-
formed on the melt processing and structure/property relations
of single phase powellite materials from oxide and carbonate pre-
cursors. A systematic examination of single phase powellite mate-
rials including structure, radiation stability and aqueous durability
provides a strong basis for understating current and future multi-
phase waste form systems.
ples were ground and analyzed by XRD from 10° to 80° two theta using CuK
1.5418 Å) on a PANalytical X-ray diffractometer (Almelo, The Netherlands).
Representative samples of select compositions were characterized to confirm
a
(
that the as-fabricated powellite ceramics met the targeted compositions and to as-
sess the potential volatility issues. The samples were prepared using lithium-
metaborate fusions followed by acid dissolution. The resulting solutions were
analyzed by Inductively Coupled Plasma
– Atomic Emission Spectroscopy
(
ICP-AES). Two measurements were taken for each element of interest, and the
Powellite is a molybdate mineral with a chemical formula of
average of these two measurements was taken as the measured value.
Most of the self-irradiation in a waste form incorporating fission products is due
to beta particle and gamma emission. These emissions cause radiation damage pri-
marily via radiolytic processes, because both beta and gamma particles induce sub-
stantial electronic excitations in a target material. Electrons provide a useful means
to examine radiolysis effects because electrons deposit nearly all of their energy in
solids via electronic loss processes. In this study, the researchers used electron irra-
diations to simulate the self-radiation damage that occurs in a material incorporat-
ing nuclides undergoing radioactive decay. In situ electron irradiations were
performed using 300 keV electrons generated in a FEI Tecnai F30 transmission elec-
tron microscope (TEM) (FEI Company, Hillsboro, OR). Powellite samples were
crushed and suspended on a holey-carbon film supported by copper grids. Electron
irradiation experiments were carried out by focusing the electron beam onto small
regions of electron transparent material (a typical irradiated region was ꢂ100 nm
4 4
CaMoO or BaMoO , and a tetragonal structure. Due to its struc-
tural variability, powellite can accommodate considerable chemi-
cal substitutions including trivalent actinides and lanthanide
elements [19]. Lanthanide-doped CaMoO
been studied for their luminescent optical properties [20]. Barium
molybdate (BaMoO ) is a promising catalyst for oxidation of soot
particulates [21], and an additive for corrosion inhibiting pigments
22]. Due to Mo–O and Mo–Mo bonds in the structure, it is also of
4
single crystals have
4
[
interest for electronic properties such as phosphor-converted light
emitting diodes (LEDs) [23,24]. It is noted that luminescence spec-
troscopy of waste forms may also reveal elemental partitioning in
distinct phases by measuring UV stimulated visible emissions from
rare earth elements (Nd, Sm, Gd) as well as molybdate structures
diameter). During these electron beam irradiation experiments, the incident elec-
tron flux, measured using a faraday cup, was approximately 1.6 ꢀ 1024 e/m2 s. Irra-
diations were performed up to a fluence of 1 ꢀ 10 e/m2 (corresponding to a dose
27
2
4
ꢁ
13
(
MoO ). The latter has been performed to investigate what hap-
of 1.5 ꢀ 10 Gy).
Raman spectra were recorded using a Renishaw InVia Raman spectrometer
pens after dissolution of a primary waste form containing Eu and
Cm. Results indicated the feasibility of re-incorporation into natu-
(
Gloucestershire, United Kingdom) equipped with a 532 nm laser light source and
ꢁ1
using a spectral resolution of 3 cm . Each sample was scanned for 20 s using a laser
power of ꢂ5 mW. For photoluminescence measurements (JY FluoroMax-4, HORIBA
Jobin Yvon Inc., Edison, NJ), a xenon light source was used to excite the samples in
the UV region (260–390 nm). Each spectrum was recorded with a 0.5 s integration
time in 1 nm intervals.
ral occurring minerals such as aragonite, a metastable CaCO
quently found in nature [25]. Raman spectroscopy has been used
in borosilicate glasses containing MoO to track the alkali and alka-
line earth molybdate crystallization during melt cooling and exam-
3
fre-
3
The ASTM C1285 Product Consistency Test (PCT) Method B was used to provide
a preliminary measure of the chemical durability of the ceramic waste forms [31].
Samples of each waste form were ground to less than 100 mesh using a tungsten
carbide grinder. All of the fine particulates were used in the PCT due to the small
quantities of material available. The surface areas of each individual sample were
determined using Brunauer–Emmett–Teller (BET) analysis (Micromeritics ASAP
2ꢁ
ine the variation of MoO4 environment in the glass structure [26].
This present work uses Raman spectroscopy to investigate the
4 4
structure of melt processed single phase BaMoO , CaMoO , and
demonstrates the potential utility to map molybdate content in
combined waste forms [27].
Powellite CaMoO has been investigated in aqueous environ-
4
ments in order to better understand the fate and behavior of
molybdenum in spent oil shale disposal environments [28]. It
2020, Norcross, GA) with nitrogen or krypton as the analysis gas prior to performing
the PCT. No washing steps were performed since the removal of fine particles would
invalidate the BET results. The PCT Method-B was performed on the selected sam-
ples in two sets. Also included were samples of the Approved Reference Material
(
ARM) glass, the Environmental Assessment (EA) glass, and blanks from the vessel
4
was found that CaMoO does not control molybdenum concentra-
cleaning batches. Stainless steel vessels were used with 15 ml of Type-I ASTM water
and 1.5 g of the ground sample. The vessels were sealed placed in an oven at 90 °C
for 7 days. Once cooled, the resulting solutions were filtered and acidified, then ana-
lyzed by ICP-AES. Normalized release rates were calculated based on the measured
compositions using the averages of the common logarithms of the leachate concen-
trations measured against the amount of exposed sample surface area using the BET
surface area measurements.
tions in spent oil suggesting the potential for good aqueous dura-
bility with respect to Mo leaching; however there has not been
extensive testing with standard corrosion tests used in waste form
characterization. The radiation effects in multiphase ceramic and
GCM waste forms have been initiated, however little is known
regarding the behavior of crystalline molybdate materials such as
powellite [29,30].
This work aims to (i) investigate BaMoO
4
and CaMoO
4
powellite
3. Results and discussion
single phase formation and morphology produced from a melt and
crystallize process which simulates expected processing conditions
of fully crystalline and composite glass/ceramic waste forms,
Fig. 1. The calcium containing powellite structure CaMoO
more negative enthalpy of formation (ꢁ1542 kJ/mol versus ꢁ1507
4
has a

1
38
K. Brinkman et al. / Journal of Alloys and Compounds 551 (2013) 136–142
also been observed in both ceramic and glass ceramic waste
forms [33]. In addition, there is a solid solution present in the
Ba1ꢁxCa MoO system, which makes the study of the single phase
CaMoO and BaMoO powellite end members a worthwhile pursuit
34].
Fig. 2 displays the XRD pattern of BaMoO
x
4
4
4
[
4
4
and CaMoO fabri-
cated from carbonate and oxide precursors by melting at 1500 °C
for 20 min followed by furnace cooling. Single phase powellite
with the scheelite structure was observed with lattice parameters
a = b = 5.23 Å, c = 11.43 Å for CaMoO
for BaMoO . Figs. 3 and 4 display the TEM bright field (BF) image,
selected area electron diffraction (SAED) and Energy-dispersive
X-ray spectroscopy (EDS) spectrum of CaMoO and BaMoO
respectively indicating the single phase nature and appropriate
stoichiometry. The lattice parameter of CaMoO based on d-spac-
ing data from SAED were calculated as a = b = 5.27 Å, c = 11.49 Å
and the BaMoO SAED determined lattice parameters were calcu-
4
and a = b = 5.58 Å, c = 12.82 Å
4
4
4
4
4
lated as a = b = 5.61 Å, c = 12.83 Å. Both values TEM SAED values
agree well with structural parameters determined from XRD.
The single phase powellite materials fabricated in this study
had larger a = b and c lattice parameters than literature values
for powellite materials formed during multiphase waste form pro-
cessing in the presence of lanthanide elements [33]. This is be-
Fig. 1. Free energy (G kJ/mol) changes with reaction from carbonate and oxide
precursors for the formation of CaMoO and BaMoO versus temperature.
4
4
2
+
2+
lieved to be due to the partial substitution of Ca and Ba for
3
+
3+
smaller lanthanide series elements such as Tb , Gd and concom-
itant point defect compensation including the formation of nega-
0
0
tively charged barium vacancy (V ) required to compensate the
Ba
3
Ba
þ
(
M 2þ ) donor substitution [35].
Fig. 5 displays the results of a series of in situ electron irradia-
tions on single phase CaMoO and Fig. 6 displays the analogous re-
sults for BaMoO . The high resolution electron microscopy (HREM)
4
4
images along with its fast Fourier transformation (FFT) diffracto-
grams clearly show the microstructural evolution of an irradiated
area. The high resolution images indicate that a crystalline to
1
3
amorphous transition occurred after 10 Gy. These results suggest
that the powellite phase materials exhibit stability to 1000 years at
1
0
11
anticipated doses (2 ꢀ 10 –2 ꢀ 10 Gy) based on current com-
mercial HLW glasses [1]. The structural change was observed on
4 4
and BaMoO
after 1013 Gy
in-situ electron irradiated CaMoO
which suggests both powellite materials have similar radiation sta-
bility upon b-particles and -emissions. It is noted that actual self-
irradiation during waste form storage would come from b-particles
fluxes which are orders of magnitude lower than that used in TEM
irradiation experiments. Whether similar radiation damage and
defect generation processes occur with low flux, long duration
b-particles exposure as compared to high flux, short duration expo-
sure to electrons in TEM experiments requires careful studies and
is the subject of substantial current efforts.
Fig. 2. X-ray diffraction (XRD) patterns of single phase CaMoO
formed by melting carbonate and oxide precursors at 1500 °C.
4
and BaMoO
4
c
4
for BaMoO ) and a more negative free energy of formation, result-
ing in the preferred powellite structure. Multi-phase glass ceramic
compositions with high levels of Mo frequently demonstrate crys-
4 4
talline CaMoO formation upon cooling [11]. However, BaMoO has
4
Fig. 3. (a) TEM bright field image and SAED and (b) EDS of melt processed CaMoO .

K. Brinkman et al. / Journal of Alloys and Compounds 551 (2013) 136–142
139
4
Fig. 4. (a) TEM bright field image and SAED and (b) EDS of melt processed BaMoO .
12
Fig. 5. High resolution transmission electron microscopy image of CaMoO
and FFT indicating amorphous transition at 1.5 ꢀ 10 Gy.
4
(a) before electron irradiation including FFT diffraction (b) 5 ꢀ 10 Gy, (c) high resolution image
1
3
12
Fig. 6. High resolution transmission electron microscopy image of BaMoO
and FFT indicating amorphous transition at 1.5 ꢀ 10 Gy.
4
(a) before electron irradiation including FFT diffraction (b) 5 ꢀ 10 Gy, (c) high resolution image
1
3
The photoluminescence (PL) of molybdates such as BaMoO
4
between 425 and 470 nm confirming the presence of a crystalline,
ordered phase and concomitant energy levels associated with vis-
ible light emission. Addition of rare earth elements present in the
have been reported in thin film and powder form as a function of
structural disorder [36–38]. It has been observed that materials
which are structurally disordered possess defects such as oxygen
vacancies, lattice defects, impurities, and local bond distortions
which yield localized electronic levels in the band gap [39]. These
electronic levels are responsible for enhancing PL emission in dis-
2+
waste stream could lead to partial substitution on the Ca or
2
+
Ba site promoting disorder in the system and favoring PL emis-
sion [30]. Therefore, photoluminescent measurements may be a
relatively easy way to evaluate powellite formation and purity in
a multiphase GCM waste form.
4
ordered materials. Fig. 7 displays the PL spectra for CaMoO single
phase powders calcined at 1100 °C for 4 h. The excitation spectrum
Raman spectroscopy is an effective tool for examining the de-
gree of structural disorder. Disordered crystals exhibit deviations
including broadening and shifting of the peaks, the appearance of
peak splitting, and peaks normally forbidden by bulk crystal
in Fig. 7a shows distinct absorptions at the 375, 405 and 430 nm,
2
ꢁ
wavelengths characteristic of [MoO
4
]
tetrahedral absorptions.
The emission spectrum of the powders in Fig. 7b shows emissions

1
40
K. Brinkman et al. / Journal of Alloys and Compounds 551 (2013) 136–142
Fig. 7. Photoluminescence of CaMoO
4
(a) excitation spectrum and (b) emission spectrum.
Table 1
4
(Ba,Ca)MoO vibrational modes and Raman peaks.
Raman peaks (cm 1
ꢁ
)
Vibrational mode
CaMoO
879
848, 795
407, 393
324
4
BaMoO
892
838, 792
360, 347
325
4
v
v
v
v
v
1
3
4
2
1
(2A )
(2F
(2F
2
)
2
)
(2E)
f.r(2F
1
) free rotation
208
146, 114
190
142, 110
ext – external modes MoO and Ca2+/Ba2+ motion
2
ꢁ
v
4
Table 2
Targeted and measured compositions (wt.%) of the powellite phases fabricated by
melting and crystallizing.
Oxide
CaMoO
4
BaMoO
4
Targeted wt.%
Measured wt.%
Targeted wt.%
Measured wt.%
BaO
CaO
MoO
Sum
–
–
51.6
–
48.4
100.0
48.3
–
46.1
94.4
28.0
72.0
100.0
26.5
68.0
94.5
3
4 4
Fig. 8. Raman spectra of CaMoO , and BaMoO .
symmetry. For the (Ba,Ca)MoO
4
system, vibrations within the
tetrahedral clusters give rise to internal vibrational
modes. External modes or lattice phonons arise from [BaO ] clus-
clusters. The Fig. 8
at 325, 792, 838 and 880 cm are indicative of internal MoO
vibrations in crystalline (Ba,Ca)MoO . The Raman peaks at 393
sitions. Of particular interest is that both powellite phases retained
approximately 95% of the targeted Mo concentrations after the
melt and crystallization process indicating relatively low volatility
of Mo from the melt. These composition measurements were used
in normalizing the PCT data. The sum of the measured oxide com-
position is less than 100% due to incomplete dissolution in the acid
solutions employed in PCT durability measurements. The constant
ratio of Ca/Mo and Ba/Mo in the targeted and measured values
indicates incomplete dissolution.
2ꢁ
[
4
MoO ]
8
2
ꢁ
4
ters and from rigid molecular unit [MoO ]
ꢁ1
4
4
ꢁ1
ꢁ1
and 407 cm in CaMoO
4
and 347 and 360 cm for BaMoO
4
are
associated with internal MoO
4
vibrations in the structure [40].
ꢁ1
Deviations from the peak center (>3 cm , the resolution of the
instrument) could be the result of different bond lengths and inter-
The PCT results for the single phase BaMoO
4 4
and CaMoO
actions between Ca, Ba and MoO
4
[41,42]. The peaks below
samples are shown in Table 3. The powellite phases had very low
ꢁ1
2
2
00 cm are indicative of external vibrations indicating a high de-
normalized release values for Ba, Ca, (<0.01 g/m ) and Mo
2
gree of crystallinity and long range order. Table 1 lists the vibra-
tional modes and Raman peaks as observed in this study These
results demonstrates the utility of vibrational spectroscopy in
monitoring molybdenum incorporation and powellite phase for-
mation nuclear waste forms.
The results of the chemical composition measurements for the
crystalline powellite phases are given along with their targeted
values in Table 2. The measured concentrations are reasonably
(<0.05 g/m ). Fig. 9 shows the calculated free energy of dissolution
2
+
2ꢁ
reaction of the powellite to M and MoO4 ions in aqueous
solution versus temperature [32]. The positive value for the free
energy change and increasing value with increasing temperature
indicate that the dissolution reaction is unfavorable. Fig. 9 also
+
+
displays the free energy of formation of Na and Cl from NaCl
showing known favorable thermodynamics for dissolution. This
behavior is similar to alkali molybdates such as Na
2 4
MoO
4 4
close to their targeted values for the CaMoO and BaMoO compo-
which are known to be water soluble. Multi-phase waste form

K. Brinkman et al. / Journal of Alloys and Compounds 551 (2013) 136–142
141
Table 3
Normalized release (g/m ) as measured by product consistency test (PCT).
Department of Energy. The authors would like to thank the Depart-
ment of Energy Office of Nuclear Energy (DOE-NE) for funding this
work under the Fuel Cycle Research and Development Program.
The authors would also like to thank J. Vienna (Pacific Northwest
National Laboratory), T. Todd (Idaho National Laboratory), and J.
Bresee (DOE-NE) for project oversight and guidance. A. Mendez-
Torres and D. Missimer gratefully acknowledged for processing
and characterization work.
2
Composition
Ba
Ca
Mo
CaMoO
BaMoO
4
4
–
0.01
0.00
–
0.01
0.05
Note: Both powellite phases retained 95% of the targeted Mo concentrations after
melting and crystallizing.
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[
[
the chemical durability of the individual BaMoO
phases is promising and melt processing of waste forms containing
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Single phase BaMoO and CaMoO were formed by melt pro-
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