Use of beryllium and beryllium oxide in space reactors

Beryllium and beryllium oxide are attractive candidate materials for neutron reflector application in space reactors due to their beneficial combination of low density and high neutron moderation and reflection capabilities. Drawbacks to their use include the expense of working with toxic materials, a limited industrial infrastructure, and material properties that are challenging in the non-irradiated state and seriously degrade under neutron irradiation. As an example of neutron effects, mechanical properties degrade under relevant conditions to the point where encasement in structural alloys is necessary. Such measures are required if neutron fluence exceeds ∼1×10²⁴ n/m² (E>0.1 MeV). At high temperatures (>500°C for Be and >600°C for BeO), irradiation-induced swelling may also limit the maximum allowable dose without additional engineering measures. Significant volumetric swelling (>5%) can occur in these materials during neutron irradiation at elevated temperatures for neutron fluences above 1×10²⁵ n/m². This paper will review Be and BeO fabrication considerations, and summarize the effects of neutron irradiation on material properties.