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Structural Design Codes: Strain-Life Method and Fatigue Damage Estimation for ITER

Panayiotis J. Karditsas

Fusion Science and Technology

Volume 29 / Number 4 / July 1996 / Pages 615-626


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A preferred route is suggested for implementing the design rules and requirements of the design codes for the International Thermonuclear Experimental Reactor (ITER), such as ASME and RCC-MR, and for preliminarily assessing which of the in-service loading conditions inflicts the greatest damage on the structure. The current ITER design schedule and possible construction time require in the short term either enhancing the existing design codes and procedures or developing new ones. The time involved in such processes is great and, when coupled with the introduction of new technology, requires adherence, as much as possible, to existing design codes; any necessary modifications to the existing framework must be minor. The rationale for using the rules for strain-deformation and fatigue limits in the design and the reasons why this method is thought to be the most appropriate for a device like ITER are presented and analyzed. Some of the relevant design code rules and constraints are presented, and lifetime and fatigue damage, with some data on fatigue life for Type 316 stainless steel, are predicted. A design curve for strain range versus the number of cycles to failure is presented, including the effect of neutron damage on the material. An example calculation is performed on a first-wall section, and preliminary estimation of the fatigue usage factor is presented. One must observe caution when assessing the results because of the assumptions made in performing the calculations. The results, however, indicate that parts of the component are in the low-cycle fatigue region of operation, which thus supports the use of strain-life methods. The load-controlled stress limit approach of the existing codes leads to difficulties with in-service loading and component categorization, whereas the strain-deformation limit approach may lead to difficulties in calculations. The conclusion is that the load-controlled approach shifts the emphasis to the regulator and the licensing body, whereas the strain-deformation approach shifts the emphasis to the designer and the structural analyst.

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