Ni-based ODS superalloy is found to be an effective candidate for a core material of Gen. IV nuclear reactors by means of a Fe/He dual-ion bombardment simulation technique. It accumulates He cavities at the dispersed oxide particle/matrix interface, and avoids the aggregation of the cavities at the other sinks even after the irradiation up to 100.1 dpa at 1000 C. Swelling was reduced less than 1%. Cavity growth and sink strengths were estimated based on TEM observation and the rate theory. The estimations support the capability of the oxide particles for trapping the He cavities and suppressing their accumulation at grain boundaries.

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The stability of cuboidal £ A precipitates under heavy irradiation was studied for newly developed Ni-based Oxide Dispersion-Strengthened (ODS) superalloys, to explore the suitability of these as core structural materials in Very High-temperature Reactors (VHTR) or Gas-cooled Fast Reactors (GFR). Ion irradiation was applied at a dose level of 100 dpa at 873 K, 1073 K and 1273 K. Under these conditions, £ A precipitates retained their cuboidal shape at 873 K, were deformed somewhat at 1073 K (as predicted by the Nelson-Hudson-Mazey (NHM) model), and were massively deformed and agglomerated at 1273 K. This deformation-agglomeration process is attributed to cascade collision, whereby the increased Gibbs free energy of the disordered phase induces a change in element distribution inside the irradiated area. Ordered, cuboidal £ A precipitates were reproduced from the disordered state after cooling and the cessation of ion irradiation.