Fundamental Studies of Irradiation Effects in Fusion Materials

Fusion is the energy production process which drives the universe. Controlled utilization of this process for the benefit of man has been the illusive goal of the world's fusion power research since the 1950s. The most easily utilized fusion reaction is the fusion of deuterium and tritium. Every major fusion power research program is directed toward utilization of the energy released from this reaction. When the hydrogen isotopes deuterium (D) and tritium (T) are fused, 80% of the energy released is carried by a single neutron. This neutron moves at 5 × 10 7 m/s and a kinetic energy of 14 MeV, so the designer of a magnetically confined reactor is faced with the reality that 80% of the power produced will impinge on the structure facing the burning plasma as a “current” of 14 MeV neutrons. The D-T reaction is illustrated in Figure 1. Neutrons are not charged and do not interact with electrons in material through which they move. They collide with nuclei. The result of these collisions is always some combination of the in-situ creation of one or more energetic ions, alteration of chemistry through transmutation, and the introduction of radioactivity. Each changes material properties. Nearly all the present experimental data base of neutron irradiation effects has come from fission reactor irradiations.