Constraint loss adjustments, based on finite element (FE) stress analysis and local critical stress, σ * , critical stressed volume, V * , cleavage criteria were applied to fracture toughness data from small pre-cracked bend bars of the IEA heat of F82H irradiated to 6.6dpa at 300°C in the High Flux Isotope Reactor. The 100MPa√m master curve method reference temperature shifts were evaluated based on both the measured toughness (ΔT m ) and after size-adjusting the toughness to small-scale yielding conditions at reference specimen size (ΔT o ) with values of ≈142 and 205°C, respectively. The model based prediction ΔT o =C o Δ〈σ fl 〉, where C o ≈0.68 and Δ〈σ fl 〉 is the change in the average flow stress over 0–10% strain is in excellent agreement with ΔT o . The FE analyses also demonstrates an upper-bound K Jc that can be measured with these small bend bars for irradiated alloys that suffer severe loss of strain hardening.