[en] This investigation provides a data base of J-R curve trends from irradiated A 508 and A 533-B weld metals exhibiting low upper shelf Charpy-V (C/sub v/) energy. These welds were made with Linde 80 flux of the same lots used for vessels currently in service. These materials exhibited postirradiation C/sub v/ upper shelf energies of 58 J to 80 J. Compact toughness (CT) specimens of four different sizes (0.5T- to 4T-CT) were characterized. These specimens were irradiated to a fluence of approx. 1 x 10¹⁹ n/cm² > 1 MeV as part of the NRC-sponsored HSST program. The J-R curves exhibited a power-law behavior for small crack extensions (e.g., < 2 mm). Irradiation decreased the level of the R-curve significantly in most cases. The value of J-integral at the initiation of crack growth (J/sub Ic/) decreased on average by approx. 25% at 200⁰C and by approx. 35% at 288⁰C. The average value of tearing modulus (T/sub avg/) was a more discriminating indication of the degradation due to irradiation, as T/sub avg/ decreased on average by approx. 54% at 200⁰C and by approx. 69% at 288⁰C. A modest size effect associated with larger specimens was indicated for tests in the unirradiated condition, while no size effect was apparent for tests in the irradiated condition. These data comppare favorably with correlations between C/sub v/ upper shelf energy and J-R curve parameters observed from prior studies with 1T-CT specimens. These correlations could enhance the significance of C/sub v/ reactor surveillance data with respect to structural integrity