One aspect of the leachability of actinide bearing glass which has not been adequately addressed is the effect of radiolysis of the system (glass-water) on the amount of actinides liberated from the glass. In the present study, we have investigated the leaching of plutonium and americium from 76–101 glass samples (containing 2 mole % plutonium) in the presence of a one megaRad/hour gamma radiation field. The presence of the radiation field was found to increase the leaching rate of both plutonium and americium by a factor of five. Speciation studies of the plutonium in the leachate indicate that the plutonium is present predominantly in the higher oxidation states, Pu(V) and Pu(VI) and that it is significantly associated with colloidal particles. Examination of the glass surfaces with X-ray photoemission spectroscopy, XPS, both before and after leaching was carried out; these studies showed lower surface concentrations of plutonium in the samples of glass leached in the radiation field.

The first observations of physical and chemical changes induced by lead implantation damage and leaching are reported for two proposed U.S. nuclear waste forms (PNL 76–68 borosilicate glass and Sandia titanate ceramics) for commercial wastes. To simulate the effects of recoil nucleii due to alpha decay, the materials were implanted with lead ions at equivalent doses up to approximately 1 × 1019 a decays/cm3 . In the titanate waste form, the zirconolite, perovskite, hollandite, and rutile phases all exhibited a mottled appearance in the transmission electron microscope (TEM) typical of defect clusters in radiation damaged, crystalline solids. One titanate phase containing uranium was found by TEM to be amorphous after implantation at the highest dose. No enhanced leaching (deionized water, room temperature, 24 hours) of the irradiated titanate waste form, including the amorphous phase, was detected by TEM, but Rutherford backscattering (RBS) suggested a loss of cesium and calcium after 21 hours of leaching. The RBS spectra also indicated enhanced leaching from the PNL 76–68 borosilicate glass after implantation with lead ions, in general agreement with the observations of Dran, et al. [6,7] on other irradiated materials. Elastic recoil detection spectroscopy (ERD), used to profile hydrogen after leaching, showed penetration of the hydrogen to several thousand angstroms for both the implanted and unimplanted materials. These basic studies identified techniques to follow the changes that occur on implantation and leaching of complex amorphous and crystalline waste forms. These studies were not designed to produce comparisons between waste forms of gross leach rates.

At the Savannah River Plant, the reference process for the immobilization of defense high-level waste (DHLW) for geologic storage is vitrification into borosilicate glass. During geologic storage for 106y, the glass would be exposed to ∼3 × 1010 rad of β radiation, ∼1010 rad of γ radiation, and 1018 particles/g glass for both α and α-recoil radiation. This paper discusses tests of the effect of these radiations on the leachability and density of the glass. No effect of the radiations was detected that reduced the effectiveness of the glass for long-term storage of DHLW even at doses corresponding to 106 years storage for the actual glass. For the tests, glass containing simulated DHLW was prepared from frit of the reference composition. Three methods were used to irradiate the glass: external irradiations with beams of ∼200 keV or Pb ions, internal irradiations with Cm–244 doped glass, and external irradiations with Co–60 γ rays. Results with both Xe and Pb ions indicate that a dose of 3 × 1013 ions/cm2 (simulating >106 years storage) does not significantly increase the leachability of the glass in deionized water. Tests with Cm–244 doped glass show no increase in leach rate in deionized water up to a dose of 1.3 × 1018 α and α-recoils/g glass. The density of the Cm–244 doped glass has decreased by 1% at a dose of 1018 particles/g glass. With γ-radiation, the density has changed by <0.05% at a dose of 8.5 × 1010 rad. Results of leach tests in deionized water and brine indicated that this very large dose of γ-radiation increased the leach rate by only 20%. Also, the leach rates are 3 to 4 times lower in brine.

The metamict transformation under electron irradiation has been studied in α-quartz using transmission electron microscopy (TEM) and convergent-beam electron diffraction (CBD). The transformation occurs in two stages: heterogeneous nucleation of discrete disordered inclusions and a slower homogeneous loss of crystalline order in the surrounding matrix. Both features are attributable to solidstate radiolysis, a mechanism for which is proposed. Ultrahigh resolution TEM structure images and information from zeroth and high order Laue zones in CBD confirm that shortrange correlations are the first to be lost and that longerrange correlations persist well into the metamict transformation. A transformation model is advanced in which progressive disorder evolves from small displacements of individual [SiO4] coordination units, made possible by lowered connectivity, within a framework of long-range ordered material.

The radiation damage of a nuclear waste glass is shown to be associated with enhanced phase decomposition, oxygen bubble formation, and, when the glass is exposed to air saturated water, enhanced leaching.

The minerals belonging to the montmorillonite group were studied. Under irradiation werp air-dry minerals as well as those in solutions containing 90Sr, which gave us an opportunity to study the irradiation influence on the soprtion accumulation of radionuclides. The analysis of the diffractograms of irradiated and nonirradiated minerals shows that the structure of the minerals belonging to the montmorillonite group remains unchanged, while alumosilicate layers converge which results in a decrease in interplane distance.

The results of previous optical absorption experiments aiming to investigate the behaviour of atomic defects in silica based glasses irradiated with various types of particles have been extended to examine the effects of multiple irradiations which take place during long term storage of glasses containing HLW. In addition, point defect clustering phenomena have been investigated by means of high voltage transmission electron microscopy. It has been found that due to the large number of defects already present in amorphous silica prior to irradiations, the contributions of different bombarding particles to the total damage cannot be considered fully additive in terms of the relative number of displaced atoms, but some consideration has to be made of defect interactions and ionization damage. Clustering effects, while being absent in pure silica, are present in borosilicates at large dose rates (≳1022 electrons m−2 sec−1 ). At lower beam current densities and doses comparable to those achieved after 10–100 years of HLW storage, phase separation into a microcrystalline compound has been detected by transmission electron microscopy.

New results on the etchability of lead implanted silicate glasses are presented which are satisfactorily accounted for by a Monte Carlo Model of etching. These results strongly support the radiation damage origin of the ion-induced modification of the chemical reactivity of glass. Major artefacts of ion implantation are then discarded as possible causes of the observed effects and consequently this technique is shown to be a valuable tool for the study of α-recoil aging in H.L.W. glasses.

The leaching behavior of a sintered Modified SYNROC-B ceramic waste form containing l0wt% simulated high level radioactive waste, under the influence of γ-irradiation, has been investigated. Similar leaching experiments have been carried out in the absence of γ-irradiation, and the leach rates of Ba and Cs are presented for comparison studies. Acid/Base formation has been monitored through pH measurements of the leachants. A decrease in pH is found with γ-irradiation due to radiolytic nitric acid generation. Higher initial leach rates with a more pronounced subsequent drop in the case of Ba and Cs were observed with γ-irradiation than without irradiation. The results of the study are presented and discussed.

Since its first R & D programme on radioactive waste management in 1973, the European Community has been contributing a steadily increasing share of the European research effort in this field. A major part of the programme is devoted to the investigation and evaluation of management concepts for high-level and TRU wastes from the backend of the fuel cycle. Risk analysis studies for the assessment of multi-barrier terminal isolation systems currently have high priority.

Nuclear fuel waste disposal research in Canada is concentrating on hard-rock disposal. The research programs concerned with the man-made components of the disposal system are reviewed. Irradiated fuel and solidified reprocessing wastes are both being researched, as are durable containers, and buffer and backfill materials. This review concentrates mainly on the more scientific aspects of the research, which contribute to the selection of preferred options for the various components of the system, and which support directly or indirectly the safety analysis of the disposal concept. Some technology development is included in the program now, and this is expected to expand as confidence in the acceptability of the disposal concept grows.

This paper describes the materials related activities of the Nuclear Regulatory Commission's (NRC's) staff in the area of high-level waste licensing of a geologic repository for nuclear waste. It frames these activities in the context of existing draft regulations for high-level waste disposal.