New Cryogenic Steels and Design Approach for ITER Superconducting Magnet System

A new design code has been developed for construction and operation/maintenance of the International Thermonuclear Experimental Reactor (ITER). A superconducting magnet system is one of the key components of ITER and its design code includes new cryogenic materials and design approach with taking account of unique features of a performance of the superconducting magnet. The new materials are nitrogen strengthened austenitic stainless steels, which have a yield strength (Sy) of over 1000 MPa and fracture toughness (KIc) of over 200 MP√m at liquid helium temperature (4K). The feature of the design approach is use of the allowable stress defined by only 2/3 Sy measured at 4K. A concept and reliability of the new design approach using new cryogenic materials for the ITER superconducting magnet system are discussed in this paper.