FOLLOWING A POST-IRRADIATION THERMAL ANNEAL CYCLE

THIS RESEARCH WILL DETERMINE THE CHARACTERISTICS OF FATIGUE INITIATION LIFE, FATIGUE CRACK GROWTH RATES, AND SLOW-STABLECRACK EXTENSIONS FOLLOWING A POST-IRRADIATION ANNEAL. FATIGUE INTITIATION LIFE WILL BE DETERMINED WITH SMOOTH SPECIMENS OF 308 STAINLESS STEEL WHICH HAVE BEEN ANNEALED AND THEN CYCLED IN PRESSURIZED, HIGH-TEMPERATURE WATER. SUBMERGED ARC WELD STEEL (LINDE 80 FLUX) WILL BE PARTIALLY FATIGUE CRACKED IN HIGH-TEMPERATURE WATER, ANNEALED IN AIR FOR ONE WEEK, AND FATIGUE CRACK GROWTH RATE TESTING WILL BE RESUMED. THESE TESTS WILL BE CAREFULLY MONITORED TO DETERMINE TRANSIENT BEHAVIOR OF CRACK GROWTH RATES. SUCH TRANSIENTS MAY ARISE FROM CHANGES IN OXIDE CHARACTER WITHIN THE CRACK TIP ENCLAVE, BUILD-UP OF CONTAMINENT SPECIES DUE TO DRYING OUT OF THE CRACK, AND CHANGES IN THE HYDROGEN EMBRITTLEMENT RATES DUE TO THE ABOVE. ENVIRONMENTALLY ASSISTED TEARING TOUGHNESS (R-CURVE) TESTS WILL BE CONDUCTEDAT SLOW DISPLACEMENT RATES, TO DETERMINE THE RATES OF CRACK EXTENSION WHICH MIGHT OCCUR DURING A POST-ANNEAL HYDROTEST. THE ENVIRONMENTALLY DRIVEN MICROMECHANISMS RESPONSIBLE FOR THIS BEHAVIOR WILL BE INVESTIGATED THROUGH CRACK SURFACE OXIDE ANALYSIS, ELECTROCHEMICAL TRANSIENT ANALYSIS AND FRACTOGRAPHY.