Irradiation creep at 60 degrees C in SUS 316 and its impact on fatigue fracture

Structural materials in fusion reactors will be subjected to irradiation by energetic particles at temperatures widely ranging from liquid He to above 1000 degreesC. Hence, the very large irradiation creep strain at 60 degree sC previously reported in the ORR/ORNL pressurized tube experiment to 8 dpa is important. Computer calculations for the 20% cold-worked SUS 316 demons trated the transient nature of this radiation-induced creep, caused by the overwhelming flux of excess interstitial atoms lasting nearly one year at 6 0 degreesC where the diffusivity of Vacancies is very low. In order to conf irm such a transient nature, continuous creep measurement under irradiation is necessary and was carried out using 17 MeV protons. Development of very significant creep strain, much larger than that at 300 degreesC, and stead ily decreasing creep rate were observed at 60 degreesC as the calculation p redicted. A significant influence of the dynamic irradiation effect at 60 d egreesC on fatigue fracture was also observed. (C) 2000 Elsevier Science B. V. All rights reserved.