In Japanese nuclear power plants, surveillance tests are conducted according to the Japan Electric Association Code JEAC4201 in order to monitor the degree of embrittlement of reactor pressure vessel (RPV) material due to neutron irradiation. Through the surveillance tests for Pressurized Water Reactor (PWR) plants, a large number of fracture toughness data have been accumulated for Japanese RPV irradiated materials. New fracture toughness curves have been developed adopting the Master Curve (MC) concept and these curves have been correlated with the Charpy V-notch 30 ft-lb transition temperature, T_r30 for evaluation against Pressurized Thermal Shock (PTS) events. The developed curves are also intended to represent the 5% tolerance lower bound of fracture toughness trend incorporating fracture toughness variation depending on the product form, which consists of plates, forgings and weld metals. In this study, the reliability of the curves is evaluated for predicted T_r30 values in consideration of application to PTS evaluation for Japanese PWR plants and it was demonstrated that the developed lower bound curve has reliability comparable to that for the measured T_r30 by adding a margin of 3 ºC to the predicted T_r30.