Formation of secondary phases after long-term corrosion of simulated HLW glass in brine solutions at 190 °C

Abstract

The behavior of rare earth elements (REE) as chemical analogues for actinides during glass corrosion was studied with static long-term batch experiments (7.5 years) at 190 • C. Corrosion tests were carried out using a simulated inactive high level waste (HLW) glass powder. Two different highly concentrated salt solutions (NaCl-rich and MgCl 2 -rich) have been used to simulate the potential corrosion by aqueous solutions in geological salt formations. Samples with surface-to-volume ratios (S/V) of 1000 m −1 and 10 000 m −1 were investigated. The chemical composition of the aqueous solution and the formation of secondary phases at the glass/solution interface as well as their elemental composition, especially with respect to the behavior of REE was studied. The glass corrosion behavior and secondary phase formation was significantly different in the two brines. In the MgCl 2 -rich salt solution, with a final pH < 3.5, hydrous Mg-silicates and (Ba,Sr)SO 4 solid solutions with considerable amounts of Sr (up to 15 wt. %) have been observed. Further, REE-sulfates and REE-molybdates with an indication of dissolution (etch pits) as secondary phases could be identified. In the NaCl-rich solution with a final high pH, REE-containing hydrous silicates (up to 35 wt. %) and (Ba,Sr)SO 4 solid solutions with small amounts of Ce (up to 5 wt. %) have been observed. Frequently observed Ca-molybdates (powellite) did not contain detectable amounts of REE.

Am(III) coprecipitation with and adsorption on the smectite hectorite

“…In aqueous environments, a reaction layer will form at the surface of the glass, followed by an alteration layer. Various neoformed secondary phases have been identified in the alteration layer of glass corroded in laboratory experiments, such as powellite and sheet silicates (Zimmer et al, 2002;Jollivet et al, 2012). The formation of such phases represents a significant retention potential for long-lived and radiotoxic radionuclides (RN), including the actinides (An), that will be released upon waste matrix corrosion.…”

Characterization of powellite-based solid solutions by site-selective time resolved laser fluorescence spectroscopy

“…Powellite has also been shown to form as a secondary mineral upon corrosion of Mo-bearing high-level nuclear waste (HLW) borosilicate glasses. 1 During this process radionuclides may form thermodynamically stable solid solutions with powellite, and thus remain effectively immobilized after the initial failure of the technological barrier. [1][2][3][4][5][6] Powellite solid solutions have also recently attracted interest from materials scientists as materials with noteworthy dielectric and optical properties.…”

“…1 During this process radionuclides may form thermodynamically stable solid solutions with powellite, and thus remain effectively immobilized after the initial failure of the technological barrier. [1][2][3][4][5][6] Powellite solid solutions have also recently attracted interest from materials scientists as materials with noteworthy dielectric and optical properties. [7][8][9][10] Powellite crystallizes in the scheelite structure with the space group I4 1 /a in which the central Ca 2+ ion is coordinated by eight singly-bound molybdate groups (Fig.…”

Trivalent actinide coprecipitation with powellite (CaMoO4): Secondary solid solution formation during HLW borosilicate-glass dissolution

“…With increasing MoO 4 2− concentration the observed peaks may suggest the formation of a 1 : 1 (at 598 nm) and a 1 : 2 (at 601 nm) complexes form (Fig. 6).…”

“…Secondary alteration phases are formed during dissolution/corrosion of the waste matrix once their solubility limit has been reached. Radionuclides, which have been released from the waste matrix may coprecipitate with these secondary phases and form thermodynamically stable solid solutions [1][2][3][4]. Powellite (CaMoO 4 ) *Author for correspondence (E-mail: bosbach@ine.fkz.de).…”