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The generation and decomposition behavior of nitrous acid is experimentally investigated during dissolution of unirradiated uranium dioxide (UO{sub 2}) pellets by a nitric acid solution. The nitrous acid is generated by the dissolution of UO{sub 2} and it then decomposes to nitrogen oxides through the solution surface. The generation rate is equal to the dissolution rate of the uranium pellet and it depends on the nitric acid concentration, solution temperature, and effective pellet surface area. The decomposition rate depends on the solution surface area and temperature. These findings allow prediction of changes in nitrous acid concentration during and after dissolution.

Experiments on cold nuclear fusion are performed on titanium deuteride (TiD{sub 2}) crystal warmed from liquid nitrogen temperature to room temperature. Fusion with an estimated thermal energy output much smaller than the expected level (10{sup 12} to 10{sup 13} fusion/s {circle dot} g{sup {minus}1}) is confirmed by neutron burst emission, but without excess heat production. In this paper by analyzing the temperature dependence of the neutron emission in the titanium-deuterium system, it is concluded that so-called cold nuclear fusion may actually be hot-spot fusion caused by a localized high voltage generated, along with fracture formation, in the TiD{sub 2} by lattice strain.

The mechanisms of radioactive corrosion product buildup on the stainless steel surface used for the primary cooling systems of boiling water reactors have been considered and the following conclusions obtained. Ionic species are taken into a spinel structure on the surface and the deposition rate is expressed as a function of exposure time and temperature of contact water. Crud is deposited on the oxide layers at a rate in proportion to the 0.82th power of the Reynolds number. Some ionic species are released from the crud on the oxide layers and are taken into a spinel structure as in item 1. Their contribution to the dose rate buildup is dominant at a dirty plant (which has a high iron content in the feedwater system). The spinel structure grows at the boundary between the oxide layers and the base metal as a result of dry corrosion of stainless steel, which involves ionic species diffusing through the oxide layers. The mechanism is supported by data from destructive measurements of the reactor water cleanup piping at Tsuruga Nuclear Power Plant.

To develop a convenient and simple low-level alpha contamination monitoring method for large quantities of radioactive wastes, a foil-type electret dosimeter was examined. For the electret material, fluoride polymer was used, and the polymer foils weer charged and polarized by applying a high voltage in air while heating at approx. =150/sup 0/C. The surface charge density of the electret foil before and after irradiation was measured by converting to a piezoelectret signal through use of a polyvinylidene fluoride. In the experiments, using a 2.5 kV/mm electric field in electret foils, an electron avalanche effect was produced, and surface charge decay was multiplied. The maximum multiplication factor obtained was approx. =200. The detection limit of alpha surface contamination was confirmed as 10/sup -6/ ..mu..Ci/cm/sup 2/ (3.7x10/sup 2/ Bq/m/sup 2/) for a 5-h irradiation time.

Melt refining as a means of uranium decontamination of metallic wastes by electroslag refining was examined. Electroslag refining was selected because it is easy to scale up to the necessary industrial levels. Various thicknesses of iron and aluminum cylinders with uranium concentrations close to actual metallic wastes were melted by adding effective fluxes for decontamination. Thin-walled iron and aluminum cylinders with a fill ratio (electrode/mold cross-section ratio) of 0.05 could be melted, and the energy efficiency obtained was 16 to 25%. The ingot uranium concentration of the iron obtained was 0.01 to 0.015 ppm, which was close to the contamination level of the as-received specimen, while for aluminum it was 3 to 5 ppm, which was a few times higher than the as-received specimen contamination level of --0.9 ppm. To melt a thin aluminum cylinder in a steady state, with this fill ratio of 0.05, instantaneous electrode driving response control was desired. Electroslag refining gave better decontamination and energy economization results than by a resistance furnace.

A low-temperature waste glass synthesis method for reducing the volatilization of radioactive high-level liquid waste (HLLW) components and the corrosion of furnace materials has been developed on a laboratory scale. This method is a sol-gel method, using the gel formation reaction of a sodium silicate solution in combination with calcination and sintering processes. Experiments to investigate the method's feasibility were conducted with nonradioactive simulated HLLW, and the glass obtained was characterized by infrared and Mossbauer spectroscopy. It was concluded that the radioactive waste glass synthesis was achieved by calcination at about 600/sup 0/C.

The mechanism of uranium adsorption from sea water by hydrous titanium(IV) oxide was investigated. The uranium adsorption experiments were conducted using a solution containing NaCl, NaHCO3, and uranium. Thermochemical calculation showed that the tris(carbonato)dioxouranate(VI) ion [UO2(CO3)3]4− found in sea water existed in the solution at pH 8 and 25 °C. The uranium uptake varied with the pH of the solution, exhibiting a minimum value at pH 8. The enthalpy change, ΔH, and the activation energy, E, of the uranium adsorption were found to be 23.6 kJ mol−1 and 52.7 kJ mol−1 respectively. The analysis of carbonate in the adsorbent showed that the carbonate ion in [UO2(CO3)3]4− was released into the solution during the uranium adsorption. On the basis of the present experimental results, the mechanism of uranium adsorption was discussed.

The adsorption of uranium from sea water with hydrous titanium(IV) oxide(HTO) was studied. HTO was prepared by mixing titanium(IV) chloride and aqueous ammonia at different pHs and temperatures. The fundamental property of HTO was investigated for apparent crystal size, specific surface area, and pore size. The uranium uptake of HTO was found to depend more strongly on the temperature than on the pH in the preparation. HTO prepared at higher temperatures exhibited larger pores and a higher uranium uptake. A kinetic study of the uranium adsorption revealed that the rate of adsorption was controlled by the particle diffusion. The diffusion coefficients were calculated.

Measurements were made of the extent of magnetization shown by composite hydrous titanium (IV)-iron (II) oxide adsorbents for use in uranium extraction from sea water. The possibility of removing the adsorbent by means of high-gradient magnetic separation was demonstrated by calculations based on a force balance model. Removal experiments were also carried out, which demonstrated that the composite hydrous oxide can be trapped effectively: A composite hydrous oxide with 1:1 Ti-to-Fe mole ratio, of 400–625 mesh particle size, proved to be removed to 99.9% by a magnetic field of 2.5 kOe, with the slurry flowing at 20 cm/s through a filter matrix 50 cm long packed to 90% void with 100 μm diameter nickel wire stuffing. Together with the evaluations made of the electric power consumed by the high-gradient magnetic separators, the experimental results indicated the possibility of economically extractng uranium from sea water using these separators in combination with magnetic adsorbents.