Determination of the Forward Rate of Dissolution for SON68 and PAMELA Glasses in Contact With Alkaline Solutions

Abstract

In the new Belgian disposal design, the nuclear waste glass will be surrounded by a 3 cm thick carbon steel overpack and a 70 cm thick concrete buffer. An initially high pH is expected after water intrusion in the concrete buffer and this may have an effect on the radionuclide release from the waste glass. This study was performed in order to determine the forward rate of dissolution for SON68 and PAMELA glasses (SM513 LW11 and SM539 HE 540-12), conducting dynamic tests at 30°C in contact with alkaline solutions. In these experiments, the silicon concentration in solution was determined by UV/Visible spectrophotometry according to the blue β-silicomolybdenum method. The forward rates of dissolution were quite similar for the three glasses except at the highest pH for which a slightly higher value was found for SM539 glass. For SON68 glass, a good agreement with the previously established interpolation law was observed until pH 11.5, but at higher pH, the interpolation law slightly overestimates the dissolution rate [1].

Determination of the Forward Dissolution Rate for International Simple Glass in Alkaline Solutions

“…In KOH solutions, we observe a general increase of the forward dissolution rate with the increase of the pH, as previously observed in literature [1,4,[8][9][10][11][12][13][14] and especially for SON68 glass in similar tests [4]. Figure 2 shows a comparison between the forward dissolution rates obtained for the first series of data obtained for ISG and SON68 in KOH solutions: a good agreement of the results is obtained for moderately alkaline pH values.…”

“…For this reason, the forward rates measured with our setup at pH 11.5-14 are probably not biased by Si resorption. The test with SON68 at pH 9 [4] did not show a clear deviation from the first-order rate law, but it cannot be excluded that the resulting forward rate was also to some extent decreased by Si resorption. It nevertheless fits with the forward rate equation found in [16], so the possible bias is probably small.…”

“…In the long term, perforation of the steel overpack will nevertheless occur, and bring the vitrified waste in contact with the highly alkaline cement pore water, causing release of the radionuclides. To better understand the waste glass dissolution kinetics in these conditions, the dissolution rates for the SON68 and the PAMELA glasses [3] were determined in alkaline media [4]. Similar tests were performed with the ISG.…”

The Interaction Between Nuclear Waste Glass and Ordinary Portland Cement

“…With 7.5 g of cement, the glass dissolution rates are higher than with 2.14 g of cement and equal to 0.038 g/m 2 /day for SON68 and 0.27 g/m 2 /day for SM539. Similar (average) rates of 0.061 g/m 2 /day for SON68 and 0.39 g/m 2 /day for SM539 were determined in dynamic leach tests previously described in with YCWCa (without cement) meaning that for both glasses, the presence of cement triggers the glass dissolution rate toward the maximum rate. Unexpectedly, the addition of 22.5 g of cement does not lead to this maximum dissolution rate.…”

“…The value of −0.32 for the pH dependence exponent was derived from dynamic leach tests in KOH solutions following the method described in . Considering the change of the glass surface area using a shrinking core model assuming spherical glass particles, the overall rate term for glass dissolution can be written as Eq.…”