To evaluate the dissolution rate of radionuclides from hull waste under geological disposal conditions, corrosion tests using a coupon type of Zircaloy 4 specimen were conducted in deoxidized deionized water at 80, 100 and 120°C by a hydrogen gas generation rate method. The corroded depth of Zircaloy was proportional to the cubic root of corrosion time at each temperature. The corrosion rate constants obtained in the present study fell on the same line on the Arrhenius plot as those at a higher temperature of around 300°C that had been obtained in material research for light water reactors. These results indicate that the corrosion mechanism of Zircaloy at 80 120°C is the same as that at the higher temperature and that an empirical corrosion rate model at the higher temperature may be applicable to a temperature below 100°C that is likely under geological disposal conditions.
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 À4 mol/L cesium iodide aqueous solution were measured with 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 À3 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 the organic 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.
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 À4 mol/L cesium iodide aqueous solution were measured with 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 À3 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 the organic 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.
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