Investigation of the high temperature steam oxidation of zircaloy 4 cladding tubes

The studies of the oxidation kinetics of the zircaloy 4/steam high-temperature reaction were continued under nearly isothermal as well as under sequence-controlled temperature-transient conditions. The first test series incorporated short-term tests in the temperature region 700-1,0000C and long-term tests at 1,0000C. Under temperature-transient conditions, pipe sections pre-oxidized to 33.5 μm ZrO2 (theoretically) were exposed, while pieces oxidized for a short time at 1,3000C were used to study the influence of a defined cooling-down velocity on oxygen uptake and structure. After the internal pipe pressure short-time tests in argon in the temperature range 800-1,3000C had been completed, tests in steam were started for 800-9500C which will be extended to the first temperature range. The influence of oxidation superposing mechanical stress on the mechanical characteristic values was measured. For 9000C, creep curves were measured at three different internal pressures by means of series of single tests. The mechanism of crack formation as a function of creep velocity was illustrated by SEM investigations. (orig./RW)