Current Understanding and Remaining Challenges in Modeling Long‐Term Degradation of Borosilicate Nuclear Waste Glasses

Abstract

Chemical durability is not a single material property that can be uniquely measured. Instead, it is the response to a host of coupled material and environmental processes whose rates are estimated by a combination of theory, experiment and modeling. High‐level nuclear waste (HLW) glass is perhaps the most studied of any material yet there remain significant technical gaps regarding their chemical durability. The phenomena affecting the long‐term performance of HLW glasses in their disposal environment include surface reactions, transport properties to and from the reacting glass surface, and ion exchange between the solid glass and the surrounding solution and alteration products. The rates of these processes are strongly influenced and are coupled through the solution chemistry, which is in turn influenced by the reacting glass and also by reaction with the near‐field materials and precipitation of alteration products. Therefore, those processes must be understood sufficiently well to estimate or bound the performance of HLW glass in its disposal environment over geologic time scales. This article summarizes the current state of understanding of surface reactions, transport properties and ion exchange along with the near‐field materials and alteration products influences on solution chemistry and glass reaction rates. Also summarized are the remaining technical gaps along with recommended approaches to fill those technical gaps.

A comparative review of the aqueous corrosion of glasses, crystalline ceramics, and metals

“…The resistance of glass to aqueous corrosion, termed glass durability, is not solely an intrinsic property of the glass, but is rather the response of glass to a range of environmental factors. 2 The reactions between alkali-boro-silicate waste glass and water include: (1) ion exchange between ionic species in water (particularly H + ) and ionic components in the glass (primarily alkali); (2) hydrolysis of network forming species (e.g., silica, boria, and alumina tetrahedra); and (3) dissolution of hydrolyzed species into solution. Through these three primary reactions, glass components are released to solution and/or are incorporated into alteration products (amorphous and crystalline phases) on the reacting glass surface.…”

Effect of thermally induced structural disorder on the chemical durability of International Simple Glass

“…Glass alteration far and close to saturation Two types of experiments were performed on the as-received and annealed fibers to investigate their initial and long-term alteration behavior, namely when the alteration process in aqueous solutions is governed by hydrolysis of the silicate network, and after by the formation of a passivating layer. 19,[39][40][41] The first series of experiments were performed under forward dissolution rate conditions at 90°C and pHs of 6, 7.5, and 9. The dissolution rates obtained from the measured silicon release rates are summarized in Table 2 and compared in Fig.…”

Impact of alkali on the passivation of silicate glass

“…However, at higher reaction progress, i.e. in conditions close to saturation, network hydrolysis is not the rate-limiting mechanism anymore, 17,18 yet the effect of alkalis on glass alteration in those conditions has not been studied.…”