Radiation-Induced Changes in Single Crystal Calcite and Dolomite: Mineral Analogues of Light Water Reactor, Nuclear Power Plant Concrete Aggregates

Two
analogues of aggregates (calcite and dolomite) found in nuclear
power plant (NPP) concrete have been neutron irradiated to fluences
up to 2 × 1020 n/cm2 at 52 °C and
4 × 1019 n/cm2 at 95 °C (E > 0.1 MeV). X-ray diffraction studies showed that these aging
conditions
affected crystallography of both calcite and dolomite, with both showing
a growth in their unit cells compared to that of the unirradiated
samples. Only dolomite samples showed a continuous increase of its
lattice parameters with the increase in irradiation. In calcites,
the lattice growth with irradiation dissipated after a fluence of
5 × 1018 n/cm2. Radiation-induced disordering
of the crystal structure was observed in both materials, while a healing
effect of irradiation temperature was mainly observed in calcites.
Dislocation densities calculated by using XRD data also supported
these observations. Insights made into the unit cells of both minerals
by using Fourier synthesis showed that the Mg sites are more prone
to the neutron irradiation than the Ca sites, resulting in larger
radiation effects and higher disruption in the crystal structure of
dolomite than that of calcite. Other than the polycrystalline characteristics
observed by using TEM, these minerals did not show complete amorphization
or significant structural decomposition at the studied irradiation
fluences.