Effects of temperature and pressure on the in-reactor creepdown of Zircaloy fuel cladding

Tests were conducted to study the behavior of Zircaloy fuel cladding under conditions that approximate those found in an operating pressurized-water power reactor. Radial surface displacement values as functions of time, average diametral-circumferential strain as a function of time, and isochronal deformation surfaces are presented. Tests were conducted at 343 degree C with external pressures from 13.3 to 18.7 MPa. Contrary to similar tests conducted out-of-reactor, the in-reactor specimens did not deform uniformly, that is, by diametral contraction and smooth ovalization. Rather, the deformation surfaces were nonuniform with hills and valleys being formed at irregular intervals. This implies that conventional concepts of creep rate and simplified modeling procedures will not work for predicting cladding behavior. 10 refs