Yusa Muroya

Sequential radiation chemical reactions in aqueous bromide solutions: pulse radiolysis experiment and spur model simulation

Pulse radiolysis experiments were carried out to observe transient absorptions of reaction intermediates produced in N2O- and Ar-saturated aqueous solutions containing 0.9–900 mM NaBr. The most important species among the reaction intermediates are BrOH˙− and Br2˙−, which commonly have absorption peaks around 360 nm. The experimental results were compared with the results of simulation based on a spur diffusion model. Each of several complicated sequential radiation-induced chemical reactions was carefully considered, optimizing its rate constant within a range of reported values, including experimental uncertainty. All the experimental results, covering a wide variety of conditions, were able to be universally reproduced by the simulation, assuming a reaction not yet reported, 2BrOH˙− → Br2 + 2OH−, with a rate constant of 3.8 × 109 M−1 s−1, which is significant only within 10 μs for rather high bromide concentrations (>10 mM). Primary G values, which are yields after sufficient diffusion from the spur to the perimeter region during 100 ns, of major water decomposition products, as well as of the reaction intermediates, were calculated for N2O- and Ar-saturated conditions as a function of NaBr concentration. Such comprehensive information on primary G values allows one to predict radiation-induced chemical change by considering only homogeneous chemical kinetics.

Analysis of the relaxation process of electron–hole pairs in α-Al2O3 using transient absorption spectroscopy

We measured transient absorption in α-Al2O3 after pulsed electron beam irradiation to analyze the relaxation process of excited states. We used two measurement systems to obtain transient absorption in nanosecond and picosecond time scales. In the nanosecond time scale, we observed a band at 610xa0nm in addition to a shoulder at 420xa0nm. This observation is consistent with that in a previous paper, and these bands are attributed to Al interstitials according to the paper. The decay behavior of these bands was significantly different in the picosecond time scale. The difference in the decay kinetics strongly suggests that the band at 610xa0nm and the shoulder at 420xa0nm are attributed to two kinds of Al interstitials.

Chemical repair activity of free radical scavenger edaravone: reduction reactions with dGMP hydroxyl radical adducts and suppression of base lesions and AP sites on irradiated plasmid DNA

Reactions of edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) with deoxyguanosine monophosphate (dGMP) hydroxyl radical adducts were investigated by pulse radiolysis technique. Edaravone was found to reduce the dGMP hydroxyl radical adducts through electron transfer reactions. The rate constants of the reactions were greater than 4 × 108 dm3 mol−1 s−1 and similar to those of the reactions of ascorbic acid, which is a representative antioxidant. Yields of single-strand breaks, base lesions, and abasic sites produced in pUC18 plasmid DNA by gamma ray irradiation in the presence of low concentrations (10–1000 μmol dm−3) of edaravone were also quantified, and the chemical repair activity of edaravone was estimated by a method recently developed by the authors. By comparing suppression efficiencies to the induction of each DNA lesion, it was found that base lesions and abasic sites were suppressed by the chemical repair activity of edaravone, although the suppression of single-strand breaks was not very effective. This phenomenon was attributed to the chemical repair activity of edaravone toward base lesions and abasic sites. However, the chemical repair activity of edaravone for base lesions was lower than that of ascorbic acid.

Material–Coolant Interactions

Basic understanding of material–coolant interactions in subcritical and supercritical water is of great importance for verifying the sustainability of supercritical water cooled reactors (SCWRs); these include such interactions as elution and corrosion of nuclear structural materials, and transportation and deposition processes along the cooling circuit. Although elution and corrosion properties in general light water reactors (at conditions from room temperature up to 300 °C) have been intensively investigated, those above 300 °C are still not well known. Thus, in the work described in this chapter, some structural materials such as type 304 and 316 stainless steels (SUS 304, SUS 316), Alloy 625 (Inconel 625) were used and model elution and corrosion experiments were conducted to obtain fundamental water chemistry data in subcritical and supercritical water (temperature range from 250 to 550 °C at 25 MPa, and in various atmospheres (deaerated and dissolved H2 or O2 conditions)).