Results from a One-Year Leach Test: Long-Term Use of MCC-L
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RESULTS FROM A ONE-YEAR LEACH TEST: LONG-TERM USE OF MCC-l*
D. M. STRACHAN Pacific Northwest Laboratory, P.
0. Box 999,
Richland, Washington,
99352,
USA
INTRODUCTION The Nuclear Waste Materials Characterization Center at Pacific Northwest Laboratory is barriers,
developing standard tests to obtain data on nuclear waste forms,
and backfills.
mal, radiation, mechanical,
These tests include performance measurements of therand chemical properties.1
Five tests have been de1
veloped to determine the chemical durability of waste forms ' static
(MCC-IP and MCC-2P) or flowing
(MCC-4S and MCC-5S)
Maximum credible release by waste forms is
2
under either
leaching environments.
determined using powders and stirred
solutions (MCC-3S). This paper presents results from the long-term use of the MCC-lP Static Leach 3
4
5
Test Method which has already been used for short-term testing ' ' and for 3,6 comparing waste forms. Data were obtained on the leaching behavior of PNL 76-68 glass over a 1-year period.
Complete solution analyses coupled with selec-
ted solid state analyses gave further insights into the mechanism of leaching for this glass and show that the MCC-lP test method can be used for periods up to at least 1 year.
EXPERIMENTAL METHODS
1 The MCC-lP Static Leach Test Method has been well documented elsewhere.
Briefly, the test requires the use of monolithic specimens leached in leachants in Teflon® PFA leach vessels under static conditions.
three
The three leach-
ants are pure water; a silicic acid/sodium bicarbonate solution; and a K, Mg, Na chloride brine.
Three temperatures may be used: 0
sults at 400C and 90 C are reported here. periodically for error analysis.
40*C,
70*C,
and 90*C.
Triplicate specimens are required
The test performed in the work for this paper
deviated slightly from the now-approved procedure but without any significant impact on the results (for example, washed in
and
Re-
specimens were cut in an organic fluid and
acetone, whereas the approved procedure calls for cutting in water).
The glass studied was the PNL 76-68 composition * This work was supported by the U.S. DE-AC06-76RLO 1830.
(Table 1).
Department of Energy under contract
182
TABLE 1. COMPOSITION OF PNL 76-68 GLASS Constituent A1 2 0 3 B2033 BaO CaO Ce02 Cr 0 23 Cs 0 Fe 200 Gd 232 0 La 2 03 MnO 2 MgO
Mass % 0.46 8.52 0.52 2.15 1.03 • 0.49 0.84 10.80 0.07 0.49 0.04 ---
Constituent
Mass %
MoO 3 Na 20 Nd2O3 NiO P 250 Ru0 Si02 SrO TeO TiO2 ZnO ZrO2
1.89 15.00 4.12 0.25 0.70 0.78 42.80 0.36 0.21 3.05 4.76 1.66
Although the Teflon® vessels used in this test were thick walled (0.26 mm) and had tight fitting lids with an internal valve, after 182 d and after 365 d in the oven.
some mass loss was noted
Since the assembled leach vessels were
not weighed at the start of the experiment,
the mass loss was estimated from the
concentration of the brine and silicate water blanks and from the known initial mass of leachant and specimen.
These estimates yielded correction factors for
the water and
Data Loading...
