Under a LOCA transient in LWRs, ruptured Zircaloy clad tubes would be oxidized at
the inner surface as well as outer surface by steam flowing in reactor core. In order to
determine whether the inner-surface oxidation influences mechanical properties of clad tubes
during the reflood stage of a LOCA, the ring compression tests were conducted on oxidized
tube specimens and segments sectioned from ruptured claddings obtained from rod-burst/
oxidation tests ranging from 1,200 to 1,500 K.
The degradation of the fracture load and the deflection at 373 K are largely influenced
by the hydrogen absorption during the inner-surface oxidation . The oxidation temperature
and the time dependence of the ductility loss of Zircaloy clad tubes can be represented by
iso-deflection lines. The iso-deflection lines due to the hydrogen absorption limit the permissible
oxidation condition to a lower temperature and shorter period of exposure time ,
comparing with sole oxygen uptake.