Inclusion of Unstable Ductile Tearing and Extrapolated Crack-Arrest Toughness Data in PWR Vessel Integrity Assessment.

摘要

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(square root of m), although arrest can be followed immediately by unstable ductile tearing. The report evaluates the influence of the crack-arrest toughness above 220 MPa(square root of m) on the integrity assessments of nuclear reactor 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(square root of m) for low-upper-shelf weld (LUSW) material and above 370 MPa(square root of m) for those vessels not containing LUSW material will usually be negated by unstable ductile tearing.