Effect of β-Phase Heat Treatment on the Subsequent α-Phase Ballooning Behavior of Zircaloy-4 Fuel Sheaths
SourceDuring certain postulated transients, a fuel sheath could experience a thermal spike into the β-phase followed by a prolonged period under stress in the α-phase temperature region. This thermal cycle would alter the metallurgical structure and the mechanical behavior. Ballooning tests were done on β heat-treated tubes to compare with previous work on as-received fuel sheaths. Comparisons were made at fixed internal pressures. Two heating rates were used—0.5 and 25°Cs-1—and the temperature range covered was 600 to 900°C. For both heating rates, in the α-phase temperature region the β heat-treated tubes strained less than as-received material at the same temperature and pressure. At temperatures in the (α + β)-phase region, there was no difference between the behavior of the two material conditions.