Four A533B pressure vessel steels containing 0.16 wt% copper, nickel and phosphorous ranging from 0.10 to 0.82 wt% and 0.006 to 0.02 wt% respectively, and a AISI 403 stainless steel, a typical end fitting material used in pressurised heavy water reactors, in the unirradiated condition, were evaluated by instrumented impact testing to determine the crack initiation energy (CVNⁱ), total absorbed energy (CVN), ductilebrittle transition temperature (T^41J,T^0.89mm), dynamic yield strength (σ^yd) and dynamic initiation fracture toughness (K^id). Three of these steels were irradiated at 563K to a nominal fast fluence of 1x10¹⁹, n/cm² (E > 1 MeV) and the corresponding parameters were evaluated.

It was observed that the widely used correlation between CVN and K^IC modified as (K^id/σ^yd)² = 0.64[(CVN/σ^yd)-0.01] overpredicted the experimental K^id values by a factor of 2. However, if the CVNⁱ was used instead of CVN, the predicted values were within ± 20%.

The irradiation induced decrease in K^id could not be correlated with increase in transition temperature. However, it could be correlated with the corresponding changes in σ^yd and CVNⁱ values.