[en] Preliminary analyses were performed for the SGTR event which occurred at Mihama-2 (Westinghouse 2-loop PWR, 500 MWe) on February 9, 1991. The analyses consisted of the transient thermal-hydraulic analysis and evaluation analysis of pressure vessel integrity during PTS (Pressurized Thermal Shock) event. The objective of the former analysis was to obtain better understanding of the event by reproducing the thermal-hydraulic behavior during the event as close as possible. The analysis successfully reproduced the overall behavior of the major plant parameters such as the primary system and secondary system pressures, pressurizer water level and so forth by adjusting the discharge coefficient for the break flow so that the calculated scram time could agree with that at the event. The objective of the latter analysis was to evaluate how severe the event was from the PTS point of view. As a result of the analysis, it was shown that the temperature decrease of the pressure vessel material at the downcomer was not large and therefore there existed sufficient margin for the propagation of the initial crack at the inner surface of the pressure vessel, even though a hypothetically large initial crack was assumed to exist. (author)