Radiation damage of nuclear structural materials and fusion reactor materials problems

Bombardment of a solid by nuclear radiation causes alterations in its physical properties. The damage pattern and some of the resulting effects may be remarkably different, depending upon the type of bombarding particles, their energy and their charge. The principal mechanisms of radiation damage are examined, with their effects on the material properties: in particular, thermal, mechanical, dimensional and electrical properties are addressed. Some particular aspects of radiation damage in steels are discussed, like for instance phase changes. The present review of main radiation damage problems in nuclear structural materials is used to introduce the particular aspects of the development of structural materials for highly irradiated components for thermonuclear fusion devices. Structural materials for a fusion reactor first wall are considered: this component is the most exposed to a high flux of energetic neutrons (14.07 MeV) and charged particles from the plasma: radiation damage is therefore one of the critical issues for such materials. Austenitic and martensitic steels are the main candidate materials, while vanadium alloys and ceramic composites need further characterization. The main characteristics of three main candidate alloys are compared. For fusion reactor materials development, it is necessary to develop models and procedures to extrapolate the effects on the materials properties at high neutron fluence, from the results of low fluence experiments. (author)