It is desirable to obtain plane strain fracture toughness data in support of plant refurbishment and plant life extension (PLEX) efforts. These data may be needed for pressurized thermal shock (PTS) analyses, low upper shelf energy analyses, and to verify shifts in the K_IR curve. A major impediment to the development of plant-specific fracture toughness data is the specimen size requirement and the fact that many surveillance capsule programs do not include fracture toughness specimens.

A new test has been developed to resolve these difficulties. An experimental modification, referred to as stress field modification, enables testing using specimens substantially thinner than those currently required by ASTM. Examination of the stress field modified specimen fracture surface demonstrates that plane strain conditions were achieved in the miniature specimens. The miniature specimens were machined from a nuclear-grade ASTM A508 steel used in the Oak Ridge National Laboratory pressurized thermal shock study. The miniature specimen data lie within the experimental scatter of the 6-in. (15.24 cm) vessel data. The development of this new fracture test enables plane strain testing of materials from surveillance programs (broken Charpy specimens) and from material cut from in-service components.