Influence of the Cooling Scenario on the Post-Quench Mechanical Properties of Pre-Hydrided Zircaloy-4 Fuel Claddings after high Temperature Steam Oxidation (LOCA Conditions)

摘要

During a postulated Loss of Coolant Accident (LOCA), fuel claddings exposed to high temperature steam oxidation may be subjected to different cooling scenarios before final water quenching (clad "rewetting"), depending in particular on the transient type. Typically, the cooling rate before the final water quenching and the final quenching temperature can vary from less than 1 °C/s up to at least 10°C/s and from about 400°C up to at least 800°C, respectively. The influence of the cooling scenario on the Post-Quench (PQ) mechanical properties of high temperature steam oxidized Zircaloy-4 cladding tubes pre-hydrided at 600 wt. ppm (typical end-of-life hydrogen content) is investigated in this paper. Ring compression and three-point bending tests were carried out at 135°C in order to characterize the PQ mechanical behavior of the oxidized, slow cooled and/or quenched specimens. Fracture surfaces of the broken specimens were observed by Scanning Electron Microscopy. Metallurgical investigations were performed to study the influence of the cooling scenario on the resultant material microstructure and the local chemical compositions.