Cladding creepdown under compression. [BWR; PWR]

Light-water power reactors use Zircaloy tubing as cladding to contain the UO/sub 2/ fuel pellets. In-service operating conditions impose an external hydrostatic force on the cladding, causing it to creep down into eventual contact with the fuel. Knowledge of the rate of such creepdown is of great importance to modelers of fuel element performance. An experimental system was devised for studying creepdown that meets several severe requirements by providing (1) correct stress state, (2) multiple positions for measuring radial displacement of the cladding surface, (3) high-precision data, and (4) an experimental configuration compact enough to fit in-reactor. A microcomputer-controlled, eddy-current monitoring system was developed for this study and has proven highly successful in measuring cladding deformation with time at temperatures of 371/sup 0/C (700/sup 0/F) and higher, and at pressures as high as 21 MPa (3000 psig)