Radiation effects on zeolite-NaY have been investigated by irradiation with a 500 keV H+ beam. The crystalline-to-amorphous transition occurs at a total dose equivalent to an ionizing energy deposition of 3×1010Gy and a displacement damage level of 0.05 dpa. The ion exchange capacity of the irradiated zeolite-NaY with 10 mN SrCl2 or 10 mN AgNO3 solutions varies with the extent of the damage to the crystalline structure. After 25 hours of exchange, the Sr concentration in the amorphous region is nearly zero. This result shows that radiation-induced amorphization can cause a significant loss in ion exchange capacity. The data also suggest that the radiation damage by proton radiation in zeolite-NaY is through both ionizing and displacement processes. The result from Ag-exchange reaction with the irradiated zeolite suggests that higher radiation dose is required to block the penetration of Ag into the supercages. The Ag concentration (∼3 at.%) in the fully damaged region suggests that the cations in the small cages are still exchangeable even when amorphization has been achieved.

A Gd-rich crystalline phase precipitated in a sodium gadolinium alumino-borosilicate glass during synthesis. The glass has a chemical composition of 45.4-31.1 wt% Gd2O3, 28.8-34.0 wt% SiO2, 10.8-14.0 wt% Na2O, 4.3-5.9 wt% Al2O3, and 10.8-14.9 wt% B2O3. Backscattered electron images revealed that the crystals are hexagonal, elongated, acicular, prismatic, skeletal or dendritic, tens of μm in size, some reaching 200 μm in length. Electron microprobe analysis confirmed that the crystals are chemically homogeneous and have a formula of NaGd9(SiO4)6O2 with minor B substitution for Si. The X-ray diffraction pattern of this phase is similar to that of lithium gadolinium silicate apatite. Thus, this hexagonal phase is a rare earth silicate with the apatite structure. We suggest that this Gd-silicate apatite in a Gd-borosilicate glass is a potential glass-ceramic nuclear waste form for actinide disposition. Am, Cm and other actinides can easily occupy the Gd-sites. The potential advantages of this glass-ceramic waste form include: 1) both the glass and apatite can be used to immobilize actinides, 2) silicate apatite is thermodynamically more stable than the glass, 3) borosilicate glass-bonded Gd-silicate apatite is easily fabricated, and 4) the Gd is an effective neutron absorber.

The solubilities of Hf and Gd in sodium alumino-borosilicate glasses based on the target compositions were examined and confirmed by electron microprobe analysis. The measured compositions of essentially crystal-free glasses are generally homogeneous and close to the target compositions. Therefore, the solubilities of Gd and Hf in sodium alumino-borosilicate glasses based on the target glass compositions are valid. However, for glasses containing precipitates (crystals grown from the melt) and undissolved HfO2 with overgrowths, the chemical compositions are often heterogeneous and may be significantly different from the target compositions. Precipitated crystalline phases include a rare earth silicate with the apatite sructure (NaGd9(Si5.25B)O26) in a gadolinium sodium alumino-borosilicate glass and a HfO2 phase in hafnium sodium alumino-borosilicate glasses.