External irradiation with heavy ions of neodymium silicate apatite ceramics and glass-ceramics

Abstract

This work aims at comparing the damage induced in the Nd silicate apatite ceramic (Ca2Nd8(SiO4)6O2) by medium energy (ME) and swift heavy ion (SHI) irradiations to evaluate the effects of nuclear collisions and intense electronic excitations for ME ions and SHI ions respectively. The macroscopic induced changes were studied as a function of the fluence by swelling and hardness measurements, whereas structural modifications were followed by X-ray diffraction, Raman spectroscopy and grazing incidence EXAFS (Nd L3-edge). At ME (1.9-6.75 MeV Au ions), radiation-induced amorphization occurred above 6.22x10 13 Au/cm 2 associated with a volume expansion of about 8% and a drop of 37% in hardness. At SHI (90 MeV Xe ions or 35 MeV Ar ions), similar macroscopic and structural changes were observed. The electronic stopping power threshold of Nd silicate apatite for amorphization was assessed at about Se = 5 keV/nm. As apatite crystals containing actinides could be present in rare-earths rich nuclear glasses, SHI irradiation with Xe (995 MeV) ions was also used to damage the Nd silicate apatite crystals dispersed in a soda-lime aluminoborosilicate simplified nuclear glass over a depth of about 60 µm, to evaluate the possible formation of cracks in the residual glass due to crystals swelling. In spite of apatite crystals amorphization under SHI irradiation in the glass-ceramics, no cracking was observed in the glassy phase even close to the biggest crystals which could be explained by strain relaxation in the glass due to plastic deformation (creep) induced by SHI ion beam.

Pyrochlore glass‐ceramics fabricated via both sintering and hot isostatic pressing for minor actinide immobilization

“…Microcracking in waste forms can lead to severely increased leach rates due to the increase in surface area for water to interact. Titanate pyrochlore is known to become amorphous under alpha self‐irradiation with several vol% swelling, 63 whereas for glasses, the swelling is generally significantly lower 64 . In a GC waste form for minor actinide immobilization, the stress induced from the swelling of the pyrochlore crystals under alpha self‐irradiation could lead to localized glass cracking.…”

“…Titanate pyrochlore is known to become amorphous under alpha self-irradiation with several vol% swelling, 63 whereas for glasses, the swelling is generally significantly lower. 64 In a GC waste form for minor actinide immobilization, the stress induced from the swelling of the pyrochlore crystals under alpha self-irradiation could lead to localized glass cracking. However, such effects can be minimized by both reducing the crystal sizes, and controlling the volume of each individual waste form pellet/HIP canister to allow the relaxation of residual glasses 64 during the swelling of pyrochlore crystals under alpha self-irradiation.…”

“…64 In a GC waste form for minor actinide immobilization, the stress induced from the swelling of the pyrochlore crystals under alpha self-irradiation could lead to localized glass cracking. However, such effects can be minimized by both reducing the crystal sizes, and controlling the volume of each individual waste form pellet/HIP canister to allow the relaxation of residual glasses 64 during the swelling of pyrochlore crystals under alpha self-irradiation. In fact, a prime advantage of HIPing is to achieve theoretical density and phase formation with minimum temperature and therefore minimum grain size.…”

Hot isostatic pressed pyrochlore glass‐ceramics: Revealing structure insides at the reaction interface

“…observed in Y 2 Ti 2 O 7 pyrochlore. 48 Given some lanthanide silicates 32,49,50 have been proven to possess good structure stability and radiation tolerance, the formation of phase 2 (Eu 1.25 SiCr 0.8 Ti 1.2 O 7.5 ) in small amounts should not have obvious detrimental effect on the overall chemical durability of the HIPed pyrochlore GC waste forms.…”

Partitioning of rare earths in multiphase nuclear waste glass‐ceramics

“…The formation of an oxyapatite phase is highly desirable, due to the flexibility to accommodate various cations of many sizes, including large fission products, and the high chemical durability due to the high fraction of SiO 2 50 . However, because minor actinides present in waste solutions can be incorporated in RE sites of the oxyapatite crystals, 48 self‐irradiation effects, including swelling and amorphization due to energy deposition by alpha decay, should be considered for both the glass and ceramic phases separately and together, and has recently been pointed out 51 …”