Development of Cryogenic Structural Materials and Structural Design Standards

From Viewpoint of Superconducting Coil Development for Fusion Reactor

Abstract

Japan Atomic Energy Research Institute (JAERI) successfully developed high field and large coils in Cluster Test Program and Large Coil Task, respectively. When these coils are designed and constructed, there were few data of ordinary 304, 316 stainless steels and no design standard. Therefore, JAERI studied effect of carbon and nitrogen on strength and toughness of 304, 316 stainless steels to determine LCT coil structural materials and adopted strength at 4K as design stress.
From these experience, JAERI concluded that it was indispensable to develop high strength, high fracture toughness and high rigidity materials and to establish design standard in order to realize superconducting coils for fusion reactor. JAERI began to develop new structural steels which had yield strength over 1, 200MPa and fracture toughness over 200MPa √m in collaboration with steel industries in 1982 and has successfully developed 6 stainless steels.
AC losses which generated in metallic materials due to pulsed magnetic field is serious problem in superconducting coils. Therefore, non-metallic structural materials which have high strength and rigidity must be developed as soon as possible. In addition, material test standards at 4K have to be established to generate data base which is used in superconducting coil design. On the other hand, design standards of superconducting coil for fusion reactor is not yet established such as ASME code in commercial fission reactor at present. However, this establishment is indispensable to design and construct high field and large superconducting coils for fusion reactor.
Development of cryogenic structural materials, evaluation technique of materials at 4K and key items to establish design standard are described here from viewpoint of superconducting coils development for fusion reactor.