Corrosion Testing of Low-Activity Waste Glasses Fiscal Year 1998 Summary Report

Abstract

SummaryAnalytical results are presented on the chemical composition and other physical properties of a glass, given the identification BNFL-A-S98, made at Pacific Northwest National Laboratory' that is representative of the low-activity waste glass composition proposed by BNFL, Inc? for immobilization of envelope A double-shell tank wastes at the Hanford Site. This glass was prepared for use in a testing program to be conducted at Pacific Northwest National Laboratory and at Argonne National Laboratory for the purpose of characterizing its long-term corrosion behavior. Detailed examination of the glass microstructure using transmission electron microscopy showed structural features indicative of amorphous phase separation. A remelt was performed on a smaller batch (100 g) to ensure rapid cooling. The glass microstructure was reexamined and showed no evidence of phase separation.Selected long-term (some to 860 d) product consistency tests were terminated, and the leachates were analyzed on tests with three other representative low-activity waste glass formulations (L8-1, L8-3, and L8-7). The results showed no evidence of corrosion rate acceleration at three times the duration of tests where another well-studied glass, LD6-5412, had been completely altered under identical test conditions. These tests (and others not discussed in this report) provide clear evidence that low-activity waste glasses with at least 20 mass% Na20 can be made that have excellent long-term corrosion resistance. However, glass composition has a large impact on long-term behavior and so careful experiments with several different techniques are essential to ensuring that a particular glass will have good long-term corrosion resistance.For example, accelerated corrosion tests were performed on the BNFL-A-S98 glass using the pressurized unsaturated flow (PUF) technique at flow rates of 0.5, 1.0, and 2.0 mL/d at 99.5"C. After only 100 to 200 h, effluent pH and electrical conductivity increased sharply, indicating a rapid acceleration in the corrosion rate of the glass. An examination of the reacted glass showed that the grains were covered with a crystalline zeolite precipitate, sodium aluminosilicate hydrate, and a thick amorphous gel layer. Crystallization of the zeolite is thought to be the cause of the observed corrosion rate acceleration because this phase acts as sink for removal of Si and A1 from the aqueous phase, which increases the chemical potential difference between the glass and solution. Measurements of alteration rinds provided an estimate of the glass corrosion rate at between 2 to 5 g/m*-d. This measurement was found to be consistent with corrosion rates calculated from chemical analysis of effluent samples and is near the expected forward rate of reaction for this glass at the test temperature and the estimated pH of pore waters in the PUF tests.A unique combination of PUF equipment and the ultracentrifugation apparatus (UFA) was developed for the quantitative assessment of changes in hydraulic properties (water retention and ...

Waste Form Release Data Package for the 2001 Immobilized Low-Activity Waste Performance Assessment

“…Because the sensor data are noisy, the data were smoothed using a bisquare weighting method where the smoothed data point, y s , is given by . The interested reader should consult McGrail et al [39] for description of the formula used to calculated normalized release rate in PUF tests. Also note that the dissolution rate of LAWABP1 glass in the PUF test is essentially identical to the dissolution rate measured in SPFT experiments in solutions near saturation with respect to amorphous silica (see Figure 8).…”

Near-field Hydrology Data Package for the Immobilized Low-Activity Waste 2001 Performance Assessment

“…Although the results reported in McGrail et al (1998) were limited, they indicate that the material behaved similarly to a fairly well-graded loam or sandy loam soil with an air-entry matric potential less than 50 cm.…”

“…The glass samples prepared by McGrail et al (1998) were packed to a porosity of approximately 0.55. Water retention and unsaturated hydraulic conductivity were measured using centrifuge methods.…”

“…Corrosion testing of potential low-activity waste glasses is discussed in McGrail et al (1998). As discussed in Section 4.2.3, this testing was performed on crushed glass samples, whereas the actual glass waste form is expected to be a highly fractured material.…”

Near-Field Hydrology Data Package for the Immobilized Low-Activity Waste 2001 Performance Assessment

“…As discussed in Section 4.2.3, this testing was performed on crushed glass samples, whereas the actual glass waste form is expected to be a highly fractured material. As discussed in McGrail et al (1998), corrosion of their crushed glass sample resulted in pronounced changes in the sample's water retention characteristic. The changes appeared to be related to the onset of precipitation of zeolitic alteration phases.…”