The diffusion rates of Na+ and Cs+ in two types of hydrous titanium(IV) oxide, precipitated at pH 6 (exchanger A) and pH 13 (exchanger B), were determined radiochemically. The rate of Cs+ in exchanger A is faster than that of Na+; diffusion coefficients are 4.9xl0-11 and 1.9xl0-11 m2 s-1 for Cs+ and Na+, respectively (pH 12, 5.0 °C). The activation energy for Cs+ diffusion is 21 kJ mol-1 and slightly smaller than that for Na+ diffusion, 29 kJ mol-1. The rates of these ions in exchanger B are much slower than those in exchanger A, and can be explained by assuming the existence of two kinds of independently diffusing ions (fast and slow species) in the exchanger. The diffusion coefficients are of the order of 10-12 and 10-13 m2 s-1 for the fast and the slow species, respectively. The activation energies are 48–60 kJ mol-1 for Na+ diffusion and 32–33 kJ mol-1 for Cs+ diffusion (pH 12). The marked difference in kinetics between two exchangers was interpreted in terms of the difference in the acid-base property and in the microstructure of the matrix.

The shaft furnace equipped with plasma-fuel burners for high temperature slagging treatment has been developed in State Corp.»RADON». A slag is considered as final wasteform. From this point of view a slag formation mechanism, radionuclides immobilization and basic slag properties have been studied. A chemical and phase compositions of institutional and nuclear power station waste slags were determined. Some details of slags structure were investigated by infra-red spectroscopy. A study of radionuclides distribution has shown that caesium and strontium are concentrated in the silicate slag constituent while iron and cobalt enter the metal fraction.

A demonstration test using radio-isotope(RI) tracers during the manufacturing of inner drum shielding material from the recycling of operating reactor scrap metal was completed and the following results were obtained. The behaviour of five radionuclides (Mn-54. Co-60. Zn-65. Sr-85 and Cs-137) was established. The time-dependent behaviors of the radionuclides in molten steel and in slag were investigated. The radioactivity distributions in metal products were homogeneous. Dose equivalent rates in the working area were below background levels and radioactive dust concentrations in the air were below detection limits.

The reducing reactions of platinum metal oxides and the formation of the complex oxides were studied to estimate the process at high temperatures. Heat treatment of Re207 with TiN causes reduction up to the sublimation point of Re207 and exhibits the highest value of the recovery among the reducing agents used in the present study. Reducing reactions of the platinum metal oxides with the reducing agents lower the melting temperature. The simplified complex oxides contain the complex oxides of the representative elements of FP and the metallic elements of the reducing agents, which contribute to a decrease of melting temperature, neodymium zirconium oxides and neodymium barium oxide which may transform to the other phases during heating. Uranium may dissolve in the phases in which uranium is identified by EPMA but cannot detected by X-ray diffraction.

Photochemical redox reaction tests were corried out where the experimental variables were irradiation rate using a Hg lamp light and molarity of nitric acid containing different reductant reagents such as hydroxylamine(HAN), hydrazine(HDZ) and urea. Based on these tests, we confirmed that the valences of Pu and Np were easily photochemically adjusted to two conditions of Pu(IV,VI)-Np(V) and Pu(IV,VI)-Np(VI), indicating that photochemical valence adjustment for the separation and co-extraction of Pu and Np has excellent potential as an advanced process technology.

The dissolution behavior of actinide and fission product metals into THF with 10 vol% Br2 was examined in this study. The solubilities of niobium, ruthenium, rhodium, zirconium and molybdenum in both aerated and nitrogenated THF solutions with 10 vol% Br2 are negligible. On the other hand, the solubilities of lanthanum, neodymium, samarium and strontium in aerated and nitrogenated THF solutions with 10 vol% Br2 are large. Among metals examined in this study, uranium had the largest solubility in nitrogenated THF with 10 vol% Br2 and under this condition uranium will be separated from other metals. In the nitrogenated organic solution U(IV), U(V) and UO22+ (VI) coexist, while only UO22+ (VI) exists in the aerated organic solution.

Regional characterisation studies of two potential host rocks for a HLW repository - the crystalline basement and the Opalinus clay of Northern Switzerland - have now been completed and documented. Application is now proceeding for the legally required federal, cantonal and communal drilling permits to initiate parallel local investigations in both these formations. The decision to continue with work in both formations is a departure from previously published plans which is intended to maximise the probability that the next major milestone in the HLW programme - demonstrating the feasibility of siting for a deep geological repository in Switzerland - can be reached by the year 2000. This paper reviews the current status of the Swiss HLW programme and outlines the planned “Phase II” site characterisation of the two chosen sites.

This study focused on developing the tracer method using the dissolved natural noble gases. The method measures precisely helium and neon dissolved in groundwater for dating. Since the dissolved helium consists of three different components (Atmospheric He, Radiogenic He and Mantle He), if it is possible to separate total dissolved helium into each component, the mixing rate between young groundwater and ancient will be predicted in in-situ groundwater. Then, dating of young groundwater is determined by measuring tritium and tritiogenic 3He in a groundwater sample. On the other hand, the dating method for old groundwater is not still verified. In this study, the old groundwater age is predicted by the accumulating rate of radiogenic helium through the alpha decay of uranium and thorium contained in rock.

This tracing method was applied to a confined aquifer in the Kumamoto plain (10km × 20km ), where the groundwater flow and the geohydrological formation of aquifer was investigated in detail in the past. The groundwater in the area consists of mixture of young groundwater (less than 20 yrs old) and ancient isolated groundwater (more than 1000 yrs old). Furthermore, the drastic change in the helium isotopic ratio revealed unexpectedly the existence of active faults covered in groundwater basins. Consequently, the method using the dissolved noble gases is practicably available for investigating the geohydrologic formation of aquifer at the early stage of the site characterization.

The geological investigations necessary for the HLW underground disposal site selection were udertaken on the contaminated territory mostly covered by vegetation and water-bodies. For lack of availiable outcrops, special attention was given to detailed petrological and geochemical studies for more reliable extrapolations. As a result, models of structure, geochemical background, and rock basement origin scenario provided general criteria for selection of geological blocks suitable for HLW deep burial.

Site restoration activities at DOE facilities and the permanent disposal of nuclear waste generated at the same DOE facilities involve working with and within various types and levels of radiation fields. Radionuclide decay and the associated radiation fields lead to physical and chemical changes that can degrade or enhance material properties. This paper reviews the impact of radiation fields on site restoration activities and on the release rate of radionuclides to the biosphere from nuclear waste forms.

An accelerated experiment using the actinide doping technique was performed to investigate the effects of alpha decay on the properties of actual nuclear waste glass at high radiation doses. A fully radioactive borosilicate waste glass, containing the actual high-level radioactive liquid waste generated from the Tokai Reprocessing Plant of PNC, was prepared by JAERI, and a powder mixture of the ground fully radioactive glass and 244CmO2 was melted at 1200°C for 2 hrs. The radioactivity concentration of 244Cm was 1.0 } 1010 Bq/g-glass at the date of preparation. The homogeneity of curium-doped glass samples was confirmed by the density measurement, heat load measurement and alpha autoradiography. The properties of the irradiated samples were investigated by the mass spectrometer for helium determination, the optical microscope, the electron probe microanalyzer, the densitometer, the Soxhlet and MCC-1 leach testing apparatus. By measuring the amount of helium released from the curium-doped glass samples, more than 99% of helium remained in the matrix at room temperature. The density of the sample slightly decreased with the increase of cumulative alpha decays and the decrease of 0.77% was observed at a dose of 1.55 } 1018 alpha decays/g, corresponding to an equivalent age of 150000 yrs. Optical and scanning electron micrographs showed that no cracks were observed on all samples having up to a dose of 1.5 } 1018 alpha decays/g. The leach rates, based on weight loss, in both the Soxhlet (100°C, 7 days) and MCC-1 (90°C, 28 days) tests did not significantly change with alpha decay dose.

Curium-doped perovskite slurry, which had the nominal composition of Ca0.98919(Cm, Pu)0.0108l Al0.0108l Ti0.98919O3, was calcined at 750°C for 2 h and then hot-pressed at 1250°C and 29MPa for 2 h. The hot-pressed cylinder samples had the specific 244Cm activity of 22.3 GBq·g−l on 31 March 1993. Their average density was 4.083 g·cm−3 after the samples got a cumulative dose of 0.7}1017 α decays·g−l. Change in density of Cm-doped perovskite reached 0.8% at a dose of 5}1017 α decays·g−l. The rate of density change was slightly larger in the present perovskite material than in Cm-doped Synroc reported previously. Half-disk perovskite specimens, which had accumulated doses of 1.6}1017 and 4.0}1017 α decays·g−l, were MCC-1 leach tested in pH˜2 solution at 90°C for two months. The leach rates of these specimens derived from weight losses were 1.7 and 2.3 g·m−2·day−l, respectively. These high leach rates caused a significant increase in pH in the later stage of the leaching runs. As-leached surfaces of Cm-doped perovskite showed the formation of anatase (TiO2). For the first 28 days, the Ca and Cm leach rates at the two different doses increased with leach time. More damaged specimens tended to give higher leach rates. In the final 28-day leaching run, both leach rates at the two different doses converged on each lower values although the Cm leach rate was lower than the Ca leach rate by a factor of >20. Nonradioactive perovskite material showed similar changes in Ca leach rate and pH to the Cm-doped one although the as-leached surfaces of the former material showed much higher degree of alteration of perovskite to anatase.

A transmission electron microscope investigation was made of zirconolites and perovskites irradiated to amorphization with 1 MeV krypton ions using the HVEM-Tandem Facility at Argonne National Laboratory. Three specimens were examined - a prototype zirconolite CaZrTi2O7, a gadolinium doped zirconolite Ca0.75Gd0.50Zr0.75Ti2O7and a uranium doped zirconolite Ca0.75U0.50Zr0.75Ti2O7. The critical amorphization dose Dc was determined at several temperatures between 20K to 675K. Dc was inversely proportional with temperature. For example, pure zirconolite requiring 10x the dose for amorphization at 475K compared with gadolinium zirconolite. Using an Arrhenius plot, the activation energy Ea for annealing in these compounds was found to be 0.129 eV and 0.067 eV respectively. The greater ease of amorphization for the gadolinium sample is probably a reflection of this element’s large cross section for interaction with heavy ions. Uranium zirconolite was very susceptible to damage and amorphised under 4 keV argon ions during the preparation of microscope specimens. In each sample, zirconolite coexisted with minor perovskite, reduced rutile (Magneli phases) and zirconia. These phases were more resistant to ion irradiation than zirconolite. Even for high gadolinium loadings, perovskite (Ca0.8Gd0.2TiO3) was 3-4 times more stable to ion irradiation than the surrounding zirconolite crystals.