Specification of stress limits for irradiated 316L(N)-IG steel in ITER structural design criteria

Austenitic steel 316L(N)-IG is one of the structural materials used in the ITER in-vessel components. For the design analysis properties of irradiated material are required. These are both stress and strain limits listed in ITER Structural Design Criteria (SDC-IC). Experimental data base on tensile properties includes irradiation up to dose of about 15 dpa in temperature range 70–500 °C. The analysis shows three temperature intervals to be treated in analysis: 20–230, 230–300 and >300 °C. For these three temperature intervals, best fit equations have been proposed. The analysis also included calculation of −95% confidence level of strength and ductility, as it is required in SDC-IC. Se and Sd stress limits have been also calculated for irradiated 316L(N)-IG steel. Those stress limits should be used in the temperature range 230–300 °C due to exhaustion of strain hardening capability of the material and decreases of uniform elongation below 2%.