A 16Cr-13Ni columbium-stabilized stainless steel (Type 1.4988) was irradiated as fuel pin cladding in the Dounreay fast reactor (DFR) and Mol BR 2 reactors and also in the Harwell Variable Energy cyclotron (VEC) up to 4.0 × 10²² n/cm²(E > 0.1 MeV) or 3 × 10¹⁷ C²⁺ ions/cm². The irradiation temperatures ranged from 300 to 650 C (572 to 1202 F). The material investigated was in an essentially solution-treated condition.

Postirradiation measurements included immersion density determinations, diametral change measurements, and transmission electron microscopy (TEM) observations.

Void formation was observed in the temperature range 350 to 600 C (662 to 1112 F). Swelling in Type 1.4988 was found to be lower than that reported previously for Types 304 and 316 unstabilized steel, especially at higher temperatures. Void concentration values at lower temperatures were comparable to those cited for 304 and 316 steels; however, they too decreased more strongly with increasing irradiation temperature. The stabilizing elements may have affected this behavior by a partial suppression of intragranular precipitates that were frequently associated with voids.