Void formation is not unique to stainless steels only; as a matter of fact, all metals and alloys swell through void formation in the homologous temperature range of 0.3-0.55Tm (where Tm is the melting point of the material in Kelvin). There may well be a variation in void swelling behavior depending on the material composi­tion, He content, grain size, temperature, and cold working. (Void formation is also a problem in the fusion technology. Fast neutrons produced from the plasma can cause void formation in the first wall blanket material with (n, a) reactions for neutron energy increasing above 5 MeV. Increase in helium content generally increases the propensity for void swelling. The problem of void swelling may be expected to be more severe in fusion reactors than in LMFBRs due to the relatively higher neutron energies.)