The development of ferritic steels for fast induced-radioactivity decay for fusion reactor applications

The CrMo ferritic (martensitic) steels are leading candidates for the structural components for future fusion reactors. However, irradiation of such steels in a fusion environment produces long-lived radioactive isotopes that lead to difficult waste disposal problems once the structure is removed from service. One method proposed to alleviate such problems is the development of steels that contain only elements that produce radioactive isotopes that decay to low levels in a reasonable time (tens of years instead of hundreds or thousands of years). For such a solution for the CrMo steels, molybdenum must be eliminated. In addition, niobium must be maintained at extremely low levels. Tungsten is proposed as an appropriate substitution for molybdenum, and the procedures for developing CrW steels analogous to the CrMo steels are discussed.