Takashi Otomo

Oxidation kinetics of low-sn Zircaloy-4 at the temperature range from 773 to 1,573 K

Isothermal oxidation tests in flowing steam were performed on low-Sn Zircaloy-4 cladding tubes over the wide temperature range from 773 to 1,573 K in order to obtain oxidation kinetics applicable to various loss-of-coolant accident conditions of LWRs. The oxidation generally obeys a parabolic rate law for the examined time range up to 3,600 s at temperatures from 1,273 to 1,573 K, and for a limited time range up to 900 s from 773 to 1,253 K. A cubic rate law is preferable for evaluating the longer-term oxidation at 1,253 K and below. The parabolic rate law constant and the cubic rate law constant for measured weight gain were evaluated at every examined temperature, and Arrhenius-type equations were determined in order to describe the temperature dependence of the rate constants. It was indicated that the change of the oxidation kinetics from the cubic to the parabolic rate and the discontinuities in the temperature dependence of the rate constants are caused by the monoclinic/tetragonal phase structure change of ZrO2.

Chemical interactions between B4C and stainless steel at hightemperatures

Abstract With a view to investigating the chemical interactions between B 4 C and type 304 stainless steel, the reaction couples ofthese two materials were isothermally annealed in the temperature range between 1073 and 1623 K. As a result of the chemical interactions, complicated reaction layers were formed at the interface of the reaction couple. To evaluate the reaction kinetics, the decrease in the thickness of stainless steel and the reaction layer growth were measured as a function of temperature and time. The overall reaction generally obeyed the parabolic rate law. Both a parabolic rate law constant and an apparent activation energy were determined. A discontinuity in the temperature dependence of the parabolic rate constants was found in the temperature range between 1473 and 1498 K. This corresponds to the formation of the liquid phase at the reaction interface.

Effects of oxygen partial pressure on oxidation of Zircaloy

Abstract The effects of oxygen partial pressure on the oxidation of Zircaloy-4 were examined at 773 K under the oxygen partial pressure between 0.1 and 2 × 10−5MPa to study the oxidation behavior of spent fuel during dry storage. The oxidation rate at first obeyed a cubic rate law, and changed to obey a linear rate law at almost the same weight gains even at different oxygen partial pressures. The oxidation rate during posttransition period showed pO20.15 dependence. The dependency of the oxidation rate in the posttransition region agreed with the results of the oxygen diffusion coefficient in zirconium oxide measured by Keneshea and Douglass. Degradation of the protective oxide film of Zircaloy-4 under low oxygen partial pressures was not observed within the oxygen partial pressure range examined. The results of this experiment showed that the oxidation rate in air can be adopted to estimate the cladding oxidation rate during dry fuel storage in air and under low oxygen partial pressures.

High temperature interaction between Zircaloy-4 and Inconel-718

Abstract The chemical interactions between Zircaloy-4 and Inconel-718 were investigated in the temperature range from 1223 to 1523 K. Multiple layers were formed at the interface of the reaction couple. The reaction generally obeyed a parabolic rate law and the rate of the reaction was determined at each examined temperature. It increased with the temperature increase. The discontinuity in the temperature dependence of the reaction rate was found at two temperatures, at about 1240 K and 1450 K. The elemental analysis with an SEM/EDX indicated that the discontinuities corresponded to the change of the reaction mechanism.

Effect of Burst Temperature on Coolant Channel Restriction in Multirods Burst Tests

In order to study the effect of burst temperature on the coolant flow channel restriction, burst tests of fuel bundles were performed. Each bundle consisted of 49 rods (7×7 rods), and bursts were conducted in flowing steam. Burst temperature was changed by changing the internal gas pressure in rods. After the burst, the ballooning behavior of each rod and the degree of coolant flow area restriction in the bundle were measured. Maximum swelling of rod occurs when the burst temperature is around α and α+β phase boundary, and this phenomenon is almost the same as that in single rod burst tests. Maximum coolant flow area restriction is also observed in this condition.