Radiation effects in Zr and Hf containing garnets

Abstract

a b s t r a c tGarnets have been considered as host phases for the safe immobilisation of high-level nuclear waste, as they have been shown to accommodate a wide range of elements across three different cation sites, such as Ca, Y, Mn on the a-site, Fe, Al, U, Zr, and Ti on the b-site, and Si, Fe, Al on the c-site. Garnets, due to their ability to have variable composition, make ideal model materials for the examination of radiation damage and recovery in nuclear materials, including as potential waste forms. Kimzeyite, Ca 3 Zr 2 FeAlSiO 12 , has been shown naturally to contain up to 30 wt% Zr, and has previously been examined to elucidate both the structure and ordering within the lattice. This study examines the effects of radiation damage and recovery using in-situ ion beam irradiation with 1 MeV Kr ions at the IVEM-TANDEM facility, Argonne National Laboratory. The complementary Hf containing system Ca 3 Hf 2 FeAlSiO 12 was also examined, and found to have a different response to irradiation damage. A sample of irradiated Ca 3 Zr 2 FeAlSiO 12 , at 1000 K, was characterised using aberration corrected (S)TEM and found to contain discreet, nano-sized, crystalline Fe rich particles, indicating a competing process during recovery is occurring.

Facile incorporation of technetium into magnetite, magnesioferrite, and hematite by formation of ferrous nitratein situ: precursors to iron oxide nuclear waste forms

“…[24][25][26][27][28] In addition, yttrium iron garnet (YIG) has been suggested as a single-phase nuclear waste form due to its ability to accommodate ions with varying charges and radii. 29,30 The similarity of the ionic radius of six-coordinate Tc(IV), 0.645 Å, to that of Fe(III), 0.645 Å, 31 respectively, suggests that Tc(IV) can replace Fe(III) in an iron oxide provided that the difference in charge is balanced. 23 Under reducing conditions, trivalent iron oxides like α-Fe2O3 are unstable towards reduction; however, 99 Tc migration is significantly slower under such conditions.…”