At intermediate temperatures and radiation doses of >10dpa, RIS effect may, in fact, lead to phase instability, involving precipitation of new phases or dissolution of existing phases. In Ni-Si system, Si as an undersize solute (atomic radius: 110 pm) compared to Ni (atomic radius: 135 pm) enriches the sinks, and when conditions are ripe, the solubility of Si in Ni exceeds the level forming new phase Ni3Si (y’-type structure). A more illustrative example is shown in Figure 6.22. Nemoto et al. [20] showed evidence of radiation-induced precipitation in various irradiated Mo-Re alloys. Precipitates formed from Mo-4Re alloys after fast neutron irradiation consist of chi and sigma phases.

6.2

Mechanical Properties

Mechanical properties are important to varying degrees in a majority of nuclear reactor components that experience a variety of loading conditions under various temperature and irradiation regimes.

6.2.1