Shinsuke Tashiro

Experiments on the Release of Gaseous Iodine from Gamma-Irradiated Aqueous CsI Solution and Influence of Oxygen and Methyl Isobutyl Ketone (MIBK)

Volatile iodine production due to radiation chemical effects is known to be an important uncertainty source in the evaluation of the source term for severe accidents of light water reactors (LWRs). The gaseous release fractions of molecular iodine and organic iodine from gamma-irradiated 10−4 mol/L cesium iodide aqueous solution were measuredwith the dose rate ∼ 7 kGy/h at room temperature. The solution was buffered with 0.1 mol/L boric acid and sodium hydroxide (pH ∼7) and contained up to 10−3 mol/L methyl isobutyl ketone (MIBK) as an organic additive. The concentrations of MIBK in the solution and oxygen in the sweep gas were changed as experimental parameters. The total iodine release fraction of the original aqueous inventory and the fraction released as organic iodine were 2–47 and 0.02–1.5%, respectively, at the end of 2 h of irradiation. They were dependent on both the aqueous MIBK concentration and oxygen concentration in the sweep gas. Under a constant cover gas condition, the total iodine release showed a decreasing trend and theorganic iodine release showed an increasing trend when the MIBK concentration increased. This behavior can be explained by the branching of the reaction path of radiolytic degradation of ketones depending on the availability of dissolved oxygen, and competition between iodine and organic compounds on the consumption of radicals produced by water radiolysis.

Characterization and storage of radioactive zeolite waste

For the safe storage of zeolite wastes generated by the treatment of radioactive saline water at the Fukushima Daiichi Nuclear Power Station, this study investigated the fundamental properties of herschelite adsorbent and evaluated its adsorption vessel for hydrogen production and corrosion. The hydrogen produced by the herschelite sample is oxidized by radicals as it diffuses to the water surface and thus depends on the samples water level and dissolved species. The hydrogen production rate of herschelite submerged in seawater or pure water may be evaluated by accounting for the water depth. From the obtained fundamental properties, the hydrogen concentration of a reference vessel (decay heat = 504 W) with or without residual pure water was evaluated by thermal–hydraulic analysis. The maximum hydrogen concentration was below the lower explosive limit (4%). The steady-state corrosion potential of a stainless steel 316L increased with the absorbed dose rate, but the increase was repressed in the presence of herschelite. The temperature and absorbed dose at the bottom of the 504 W vessel were determined as 60 °C and 750 Gy/h, respectively. Under these conditions, localized corrosion of a herschelite-contacted 316L vessel would not immediately occur at Cl− concentrations of 20,000 ppm.

Release of radioactive materials from high active liquid waste in small-scale hot test for boiling accident in reprocessing plant

The release behavior of radioactive materials from high active liquid waste (HALW) has been experimentally investigated under boiling accident conditions. In the experiments using HALW obtained through laboratory-scale reprocessing, the release ratio was measured for fission product (FP) nuclides such as Ru, Tc-99, Cs, Sr, Nd, Y, Mo, Rh and actinides such as Cm-242 and Am-241. As a result, the release ratio was 0.20 for Ru and was around 1×10−4 for the FP and actinide nuclides. Ru was released into the gas phase in the form of both mist and gas. For its released amount, weak dependency was found to its initial concentration in the test solution. The release ratio decreased with the increase in the initial concentration. For other FP nuclides and actinides as non-volatile, released into the gas phase in the form of mist, the released amount increased with the increase in the initial concentration. The release ratio of Ru and NOx concentration increased with the increase in the temperature of the test solutions. They were released together almost at the same temperature between 200 and 300 °C. Size distribution of particles like mist was measured. The data show that there was a difference between distributions at the temperatures below 150 °C and over 200 °C.

Experiment and Modeling for Solvent Leaching from Paint Matrix Considering Equilibrium

The leaching behavior of remaining solvent from an epoxy paint coating when it is submerged in water was experimentally studied. A leach kinetics model considering the equilibrium of the solvent concentration in the paint matrix and in water was developed. Three model parameters, equilibrium constant K, leaching rate kd , and initial concentration of the solvent in the paint C0 p, were evaluated based on the experimental results, and empirical correlation equations for them were obtained. The model showed good qualitative and quantitative agreement with the observed evolution of the leached solvent mass in the present experiment. Also, the model showed consistency with experimental data in a different configuration.