Direct Experimental Evidence for Differing Reactivity Alterations of Minerals following Irradiation: The Case of Calcite and Quartz

Abstract

Concrete, used in the construction of nuclear power plants (NPPs), may be exposed to radiation emanating from the reactor core. Until recently, concrete has been assumed immune to radiation exposure. Direct evidence acquired on Ar+-ion irradiated calcite and quartz indicates, on the contrary, that, such minerals, which constitute aggregates in concrete, may be significantly altered by irradiation. More specifically, while quartz undergoes disordering of its atomic structure resulting in a near complete lack of periodicity, calcite only experiences random rotations, and distortions of its carbonate groups. As a result, irradiated quartz shows a reduction in density of around 15%, and an increase in chemical reactivity, described by its dissolution rate, similar to a glassy silica. Calcite however, shows little change in dissolution rate - although its density noted to reduce by ≈9%. These differences are correlated with the nature of bonds in these minerals, i.e., being dominantly ionic or covalent, and the rigidity of the mineral’s atomic network that is characterized by the number of topological constraints (nc) that are imposed on the atoms in the network. The outcomes have major implications on the durability of concrete structural elements formed with calcite or quartz bearing aggregates in nuclear power plants.

Rate controls on silicate dissolution in cementitious environments

“…In general, dissolution rates were quantified whereby: (i) a collection of (fly ash) particles were embedded in an inert substrate, or (ii) a planar mineral/synthetic glass surface that is partially covered with an inert silicone film (i.e., "masked", see Fig.1(a) are submerged in a static drop or fixed volume of solution for a prescribed time interval [16,32,[35][36][37][38]. In all cases, a high liquid-to-solid mass ratio (l/s, ≥ 500) is used with contact times ranging on the order of minutes (glasses) to hours (albite) depending on the solid's aqueous dissolution rate.…”

“…Vertical scanning interferometry (VSI) for measuring aqueous dissolution rates: The average dissolution rates of the fly ash, mineral, and glass samples were measured at room temperature (298 K) using vertical scanning interferometry (VSI) [31,32]. VSI offers the ability to acquire three dimensional-visualizations of reacting surface topographies with nanoscale vertical resolution (≈1-2 nm) over sample areas on the order of 10s of mm 2 .…”

Review of the Current State of Knowledge on the Effects of Radiation on Concrete

“…Irradiated-amorphous silica also shows, to a lesser extent, a greater susceptibility to dissolution (Ichikawa and Koizumi 2002). Conversely, irradiationinduced density change in calcite is essentially caused by rotations and distortions of the carbonate groups with respect to the Ca atom positions leading to minor change of the dissolution rate (Pignatelli et al 2016). The increasing reactivity of irradiated aggregate is one factor driving the formation of alkali-silica reaction gels.…”

“…Ion-implantation-induced disorder (amorphization) of the three-dimensional framework silicates, α-quartz (Ichikawa and Koizumi 2002;Pignatelli et al 2016) and plagioclase (Ichikawa and Kimura 2007) results in an increase by several orders of magnitude of the dissolution rate in contact with a highly alkaline solution close to that of unirradiated amorphous silica (Pignatelli et al 2016). Irradiated-amorphous silica also shows, to a lesser extent, a greater susceptibility to dissolution (Ichikawa and Koizumi 2002).…”

“…Amorphization is predominantly observed in silicatebased minerals. For example, while quartz presents strong long-order radiation-induced disordering, irradiation of calcite causes primarily the rotation of the carbonate groups (Pignatelli et al 2016). The critical CA dose in silicates depends on several factors: (1) the melting temperature; (2) a structural factor (e.g., degree of SiO 4 polymerization, elastic properties); and (3) the proportion of Si-O bonding (Eby et al 1992).…”