[en] Over the past several years, the Heavy-Section Steel Technology Program at Oak Ridge National Laboratory has performed a series of large-scale fracture-mechanics experiments. These experiments have demonstrated that prototypical nuclear reactor vessel steels can exhibit crack-arrest toughness values considerably above 220 MPa·√m, although arrest can be followed immediately by unstable ductile tearing. This report evaluates the influence of the crack-arrest toughness above 220 MPa·√m on the integrity assessments of nuclear rector pressure vessels for pressurized-thermal shock (PTS) loading conditions, taking into account the potential for unstable ductile tearing following arrest. The influence of the high crack-arrest toughness data and unstable ductile tearing on pressurized-water reactor vessel integrity assessment is PTS transient dependent. However, it appears that the potential benefit from crack-arrest events corresponding to toughness values above 240 MPa·√m for low-upper-shelf weld (LUSW) material and above 370 MPa·√m for those vessels not containing LUSW material will usually be negated by unstable ductile tearing. 26 refs., 19 figs