In this work, we have studied the reaction between H 2 O 2 and UO 2 with particular focus on the nature of the hydroxyl radical formed as an intermediate. Experiments were performed to study the kinetics of H 2 O 2 consumption and uranium dissolution at different initial H 2 O 2 concentrations. The results show that the consumption rates at a given H 2 O 2 concentration are different depending on the initial H 2 O 2 concentration. This is attributed to an alteration of the reactive interface, likely caused by blocking of surface sites by oxidized U/surface-bound hydroxyl radicals. The dissolution yield given by the amount of dissolved uranium divided by the amount of consumed hydrogen peroxide was used to compare the different cases. For all initial H 2 O 2 concentrations, the dissolution yield increases with reaction time. The final dissolution yield decreases with increasing initial H 2 O 2 concentration. This is expected from the mechanism of catalytic decomposition of H 2 O 2 on oxide surfaces. As the experiments were performed in solutions containing 10 mM HCO − 3 and a strong concentration dependence was observed in the 0.2-2.0 mM H 2 O 2 concentration range, we conclude that the intermediate hydroxyl radical is surface bound rather than free.

Hydrogen production by g-radiolysis of the mixture of mordenite, a zeolite mineral, and seawater was studied in order to provide basic points of view for the influences of zeolite minerals, of the salts in seawater, and of rise in temperature on the hydrogen production by the radiolysis of water. These influences are required to be considered in the evaluation of the hydrogen production from residual water in the waste zeolite adsorbents generated in Fukushima Dai-ichi Nuclear Power Station. As the influence of the mordenite, an additional production of hydrogen besides the hydrogen production by the radiolysis of water was observed. The additional hydrogen can be interpreted as the hydrogen production induced by the absorbed energy of the mordenite at the yield of 2.3610 78 mol/J. The influence of the salts was observed as increase of the hydrogen production. The influence of the salts can be attributed to the reactions of bromide and chloride ions inhibiting the reaction of hydrogen with hydroxyl radical. The influence of the rise in temperature was not significantly observed up to 608C in the mixture with seawater. The results show that the additional production of hydrogen due to the mordenite had little temperature dependence.

Radiation-induced oxidative dissolution of uranium dioxide (UO2) is one of the most important chemical processes of U driven by redox reactions. We have examined the effect of UO2 stoichiometry on the oxidative dissolution of UO2 in aqueous sodium bicarbonate solution induced by hydrogen peroxide (H2O2) and γ-ray irradiation. By comparing the reaction kinetics of H2O2 between stoichiometric UO2.0 and hyper-stoichiometric UO2.3, we observed a significant difference in reaction speed and U dissolution kinetics. The stoichiometric UO2.0 reacted with H2O2 much faster than the hyper-stoichiometric UO2.3. The U dissolution from UO2.0 was initially much lower than that from UO2.3 but gradually increased as the oxidation by H2O2 proceeded. Increase in the initial H2O2 concentration caused decrease in the U dissolution yield with respect to the H2O2 consumption both for UO2.0 and UO2.3. This decrease in the U dissolution yield is attributed to the catalytic decomposition of H2O2 on the surface of UO2. The γ-ray irradiation induced the U dissolution that is analogous to the kinetics by the exposure to a low concentration (2 × 10–4 mol dm–3) of H2O2. The exposure to higher H2O2 concentrations caused lower U dissolution and resulted in deviation from the U dissolution behavior by γ-ray irradiation.

The radiation stability of the candidate An(III)/Ln(III) separation ligand hexa-n-octylnitrilo-triacetamide (HONTA) under envisioned process conditions was investigated using a combination of solvent test loop gamma and pulsed electron irradiation.

The absorption spectra of Br(2)(•-) and Br(3)(-) in aqueous solutions are investigated by pulse radiolysis techniques from room temperature to 380 and 350 °C, respectively. Br(2)(•-) can be observed even in supercritical conditions, showing that this species could be used as a probe in pulse radiolysis at high temperature and even under supercritical conditions. The weak temperature effect on the absorption spectra of Br(2)(•-) and Br(3)(-) is because, in these two systems, the transition occurs between two valence states; for example, for Br(2)(-) we have (2)Σ(u) → (2)Σ(g) transition. These valence transitions involve no diffuse final state. However, the absorption band of Br(-) undergoes an important red shift to longer wavelengths. We performed classical dynamics of hydrated Br(-) system at 20 and 300 °C under pressure of 25 MPa. The radial distribution functions (rdf's) show that the strong temperature increase (from 20 to 300 °C) does not change the radius of the solvent first shell. On the other hand, it shifts dramatically (by 1 Å) the second maximum of the Br-O rdf and introduces much disorder. This shows that the first water shell is strongly bound to the anion whatever the temperature. The first two water shells form a cavity of a roughly spherical shape around the anion. By TDDFT method, we calculated the absorption spectra of hydrated Br(-) at two temperatures and we compared the results with the experimental data.

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We have investigated the ultrasonic velocity-change (UVC) imaging method to detect unstable vessel plaques using the difference in the temperature coefficient of ultrasonic velocity between water and fat. Thus far, to obtain effective ultrasonic velocity changes in the UVC imaging method, a warming procedure using a laser or an ultrasonic wave has been used. In this study, we utilize a cooling procedure instead of the warming procedure for this imaging method. As a result, lipid areas inside a carotid artery phantom were more clearly identified in the UVC image obtained under cold exposure.

The role of intermediate phases in CeO 2 mesocrystal formation from aqueous Ce III solutions subjected to g-radiation was studied. Radiolytically formed hydroxyl radicals convert soluble Ce III into less soluble Ce IV .T ransmission electron microscopy( TEM) and X-rayd iffraction studies of samples from different stages of the process allowed the identification of several stages in CeO 2 mesocrystal evolution following the oxidation to Ce IV :(1) formation of hydrated Ce IV hydroxides,s erving as intermediates in the liquid-to-solid phase transformation;(2) CeO 2 primary particle growth inside the intermediate phase;( 3) alignment of the primary particles into "pre-mesocrystals" and subsequently to mesocrystals, guided by confinement of the amorphous intermediate phase and accompanied by the formation of "mineral bridges". Further alignment of the obtained mesocrystals into supracrystals occurs upon slow drying, making it possible to form complex hierarchical architectures.