Burial Effects on Nuclear Waste Glass
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BURIAL EFFECTS ON NUCLEAR WASTE GLASS LARRY L. HENCH*, LARS WERME** AND ALEXANDER LODDING*** *Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, USA; **SKBF/KBS, Stockholm, Sweden; ***Chalmers University of Technology, Gothenburg, Sweden.
INTRODUCTION The purpose of this experiment was to evaluate the effects of various components of the SKBF/KBS nuclear waste storage system on the leaching of the vitreous waste form. Two cohfigurations of nuclear waste glasses, canisters, overpacks, and backfill mate-7ial were inserted into 5.6 cm x 3 m deep boreholes located at the 350 m level in the STRIPA mine. Some were maintained at 90 0 C. The others were allowed to equilibrate at the ambient temperature of the mine, approximately 80 C.
Two borosilicate
nuclear waste glass compositions (termed ABS 39 and ABS 41) compatible with the French AVM process containing 9 percent by weight of simulated fission products were compared. The two compositions ( Table 1) bracket the range of Si02/Na 2O/B2 0 3 ratios likely to be selected for commercial vitrification operations at La Hague. Table 1 Glass composition (weight %) lassSiO2B20 AI23 oxide gls i 23A23N2
N20
F203ZnO e0
Li20
U02 simulated fission products
ABS 39
48.5
19.1
3.1
12.9
5.7
0
0
1.7
9
ABS 41
52.0
15.9
2.5
9.9
3.0
3.0
3.0
1.7
9
One configuration tested (called "pineapple slices") involved thin, right circular discs of glass with a central hole for a heater rod. The sequence of interfaces are shown in Fig. 1. One side of each sample was polished to 600 grit SiC, the standard used for correlative lab tests. The alternate side was left rough in order to avoid mixing interfaces during disassembly. The second configuration, called minicans, 2 cation.
is described in another publi-
Static leaching laboratory experiments were also conducted at 90 0 C to compare with the in-situ burial results and to isolate the interfacial variables. A procedure similar to MCCI was used.
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The variables investigated
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included:
glass composition ratio of glass surface area to volume of
leachant solution (SA/V=cm-
1
);
presence or absence of compacted bentonite 3
3
exposed to the leachant solution; ratio of cm
bentonite to cm water;
presence of granite together with compacted bentonite, 3
ratio of cm
3
granite to cm water.
glass, and water;
Detailed results from this extensive
series of tests are presented in another publication.
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EXPERIMENTAL METHODS Surface analyses of the samples were made using both infrared reflection spectroscopy (IRRS)
5 7
'
ion beam profiling. '
6
and secondary ion mass spectroscopy
8
(SIMS) with
Areas of samples used for IRRS were photographed
using reflection optical microscopy at 120X magnification.
From 4-8 spots
were analyzed per sample with IRRS and the spectra reported represent the range of changes observed. for the 1120 cm-
1
All spectra were normalized to a value of 80
Si-O-Si molecular stretching vibration of vitreous SiO2
by use of a shutter in the re
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