Study on Fundamental Processes of Formation, Conversion and Dissolution of Crud in Nuclear Reactor Environments.

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1) Formation and characterization of simulated crud : Magnetite with different composition was prepared by five different methods, and reactivities of various iron oxides and hydroxides with Ni(OH)_2 and Co(OH)_2 were investigated. The reactivity of gamma-FeOOH with Ni(OH)_2 and Co(OH)_2 was extremely high, and gamma-FeOOH formed NiFe_2O_4 and CoFe_2O_4 at 150-300ﾟC.The reactivities of alpha-FeOOH and alpha-Fe_2O_3 with Ni(OH)_2 were low, but fine alpha-FeOOH and alpha-Fe_2O_3 were reactive towards Ni(OH)_2. Fe_3O_4 did not react with either Ni(OH)_2 or Co(OH)_2.2) Dissolution mechanism of magnetite : Conditions of solutions (pH, concentrations of hydrazine and EDTA, and temperature) against dissolution rates of magnetite were investigated and the mechanism of dissolution was estimated. In the solutions wit13EA\ : hout hydrazine, dissolution rates of magnetite obeyed to parabolic rate law in pH 5-10. At pH 4, dissolution proceeded in two stages ; the first stage obeyed paraboric rate l … More aw, and the second the rate law with time exponent of 2. In the solutions c13EA\ : ntaining hydrazine, dissolution proceeded in two stages ; the first stage obeyed the parabolic rate law, and the second stage linear rate law at concentrations of 0.001-0.003 mol dm^<-3>, and the first stage obeyed linear rate law, and the second sta13EA\ : ge the rate law with time exponent of 2 at the concentrations of 0.005-0.010 mol dm^<-3>.3) Construction of data base in connection with chemical decontamination : The construction of a data base of the formation, conversion, dissolution and decontamination of crud was attempted in connection with the chemical decontamination of coolant13EA\ : circuits of water-cooled nuclear rreactors. In addition, the results of searches about the formation and conversion of various iron oxides, and the formation of spinel compounds were demonstrated in connection with crud formation. The searches were13EA\ : also carried out on the modelling of crud behaviors, the activation of crud and the decontamination of coolant circuits of reactors. Less