Fracture toughness testing on standard specimens in the ductile to brittle transition regime is well established and standardized by the ASTM since 1997. However, its applicability to structural components and its potential conservatism remain a subject of concern. In structural integrity assessment of reactor pressure vessels submitted to an accidental loading condition called pressurized thermal shock, the cladding is generally considered not to play any role and is neglected. However, cladding has the ability to restrain the crack from opening due to its good ductility. To investigate the potential safety margin, a semielliptical crack introduced by fatigue is covered by a stainless steel cladding and specimens are tested under biaxial conditions in the ductile to brittle transition regime. Test results shows that cladding plays a significant role and contributes to an additional safety margin. In addition, cladding increases the potential for crack arrest.