In order to predict fracture behavior of a structure with low constraint, tensile fracture tests using flat plate specimens with a surface flaw were performed at −80°C and −120°C in the ductile-brittle transition temperature (DBTT) region. The shape of the flat plate was 50mm thickness, 200mm width, and 500mm length. A semi-elliptical flaw of 5mm depth and 25mm length was introduced on the specimen’s surface. The measured KJ at fracture of the flat plate specimens were located between the predicted fracture probability bound of 5% and 95% of KJc from the laboratory specimen, C(T) and SE(B), including those for bending load obtained in the previous paper of the PVP2021 conference, Report 1. The Weibull parameters of the Weibull stress, m and σu, for the Beremin model and the parameters of the GTN model from the laboratory specimens, SE(B) and C(T) specimens, were used for the fracture probability prediction. Based on this verification result of the prediction procedure using the coupled model of the Beremin model and the GTN model, the plastic constraint correction coefficient χ, was proposed for fracture evaluation of a reactor pressure vessel. For simplification of the fracture evaluation, uniaxial loading plate models which accurately simulate the mechanical behavior of a reactor pressure vessel for representative PTS transients were applied for calculation of the coefficient χ.