Effect of Overpack Materials on Glass Leaching in Geological Burial
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EFFECT OF OVERPACK MATERIALS ON GLASS LEACHING IN GEOLOGICAL BURIAL LARS WERME*, L. L. HENCH** AND ALEXANDER LODDING*** *SKBF/Div. KBS, Stockholm (Sweden); **University of Florida, Gainesville, Florida (USA); ***Chalmers University of Technology, Gothenburg (Sweden) INTRODUCTION This is one of two papers discussing the findings in an in situ-burial experiment, presently being performed in the Stripa mine in Sweden.
The purpose of the experiment is to evaluate the effects of various components in the SKBF/KBS waste storage system on the leaching of the vitreous waste form. Two configurations of glass, canister, overpack and buffer/backfill materials were designed (Figs. 1 and 2). Both configurations were inserted into 56 mm diameter boreholes in the Stripa mine and maintained at 90*C. One of the configurations (Fig. 2) was also kept at ambient temperature, 8*C. In the experiments two glass types were used, ABS 39 and ABS 41 (Table 1). These glasses, developed by Dr. T. Lakatos of the Swedish Glass Research Institute, contain 9% simulated fission products by weight and are compatible with the French AVM process. One configuration, Fig. 1, is deTABLE 1
signed to simulate closely a waste
GLASS COMPOSITION (WEIGHT %)
package in a disposal hole, as described in the KBS concept 2. The small "minicanisters" contained ABS 39 or ABS 41
Oxide
ABS 39
ABS 41
SiO2
48.5
52.0
B2 03
19.1
15.9
Al203 Na 20
3.1 12.9
2.5 9.9
Fe 20 3
5.7
3.0
ZnO
0
3.0
Li20
0
3.0
UO2
1.7
1.7
Simulated fission products
glass cast into chromium-nickel steel cylinders.
Upper and lower surfaces
of the minicanisters were polished to a 600 grit surface finish after a concentric center hole was bbred for a center heater rod.
The minicanisters
were then arranged to provide glassglass or glass-betonite interfaces (Fig. 2).
Sleeves of lead and titanium
or copper overpacks were placed around 9
9
the steel wall of the minicanister, and a bentonite buffer sleeve separated the waste package from the walls of the borehole in the granitic rock.
136
In
the second configuration, described in detail in ref.
of glass,
granite,
1, circular discs
bentonite and various overpack metals are stacked around
a central tube containing a heater rod, to maximize the number of interfaces between glass and other materials (Fig. 3).
This configuration is
also
referred to as the "pineapple slice" configuration, due to the shape of the discs. Both configurations provide interfaces between the glass and the other components in
the SKBF/KBS waste storage system.
However,
the "pineapple slice" configuration (28 vs 8)
maximized in
most experiments were performed using that configuration.
the interfaces are and consequently In this paper only
interactions between the glass and the metallic overpacks are discussed.
Other
burial effects are described elsewhere. EXPERIMENTAL METHODS For the characterization of the glass surfaces, have been used:
three different metho
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