Post-test examination and evaluation of the CORA experiments

CORA-B and CORA-C out-of-pile experiments performed in the CORA test facility are reported. A bundle of 9 unheat and 16 electrically heated fuel rod simulators consisting of Zircaloy-4 cladding, annular alumina pellets, and central heater rod) had been submitted to a temperature-transient of roughly 20000C peak temperature. CORA-B was run under argon atmosphere but with a water-cooled lower bundle head, CORA-C was performed under steam. Both bundles showed comparable damage from steam oxidation, melting and chemical interaction of the metallographically prepared cross sections. Microstructures of Zircaloy-4 tube specimens from earlier high-temperature steam oxidation investigations are discussed. The oxide layer formation and the melting and cladding/scale interaction processes are presented in a sequence of microstructural examples. (orig./DG)