For S-65C Be grade irradiated up to 1025nm~2 (~0.74dpa) at ~300 °C, the thermal conductivity was found to be similar, within experimental error, to that of the unirradiated material.146 Similarly, no effect was seen for Be S-65C after irradiation at 350 and 700 °C to a damage dose ~0.35dpa.147 Significant changes in the thermal conductivity were observed only for conditions that lead to sig­nificant changes of the beryllium structure, such as the formation of a high density of radiation defects (especially at low irradiation temperature and high dose) or high (more than tens ofpercent) swelling.144

Other physical properties (elastic modulus, coef­ficient ofthermal expansion, etc.) are not influenced by neutron irradiation (at least at the fluence and temperature ranges relevant for the beryllium armor for the ITER PFCs).

4.19.4.4.1 Swelling

It is well known that beryllium swells when irradiated by neutrons, especially during high temperature irradiation. Reviews of the available swelling data for different Be grades can be found elsewhere (see, e. g., ITER MAR,129 Billone,139 and Barabash eta/.141). The computer code ANFIBE (ANalysis of Fusion Irradiated BEryllium), has been developed and applied in the past as an interpretative and predictive tool148 for the prediction of beryllium swelling. The driving force for the swelling is the presence of He, which forms He bubbles, especially during high-temperature irradiation (more than ^400 °C) or after high-temperature annealing. The maximum values of swelling could reach approximately tens of percent at temperatures more than 600 °C and helium content more than several thousand atomic parts per million. Swelling depends on the structure of the beryllium: beryllium grades with small grain size (~8—10 pm) and high BeO content (~3-4wt%) have a higher resistance to swelling than conventional Be grades.141 As concluded in ITER MAR,129 for an irradiation temperature <^400 °C, swelling of beryl­lium containing 1500 appm He is <~1%. At higher temperature, swelling could reach the value of a few percent at the end of life.