A Theoretical Model for Determination of Fracture Toughness of Reactor Pressure Vessel Steels in the Transition Region from Automated Ball Indentation Test

This paper presents KAERI's independently developed theoretical framework for extending ABI® fracture toughness estimation to the ductile-to-brittle transition region — the most safety-critical temperature range for nuclear reactor pressure vessels.

The KAERI team derived a fracture stress model as a function of stress triaxiality under the ball indenter, enabling more rigorous toughness estimates for RPV steels in the transition regime where fracture behavior changes from fully ductile to fully brittle. This transition region is where reactor vessels are most vulnerable to pressurized thermal shock, making accurate toughness characterization essential.

The significance of this paper lies in KAERI's independent theoretical development — building on Haggag's foundational work but developing their own analytical framework. This independent theoretical contribution by a major national nuclear research laboratory validated not just ABI®'s experimental capability but its underlying physical principles.