Abstract Shin Kori unit 3 of Korea Hydro and Nuclear Power Co. is the pressurized water reactor of advanced power reactor 1400 (APR1400) in the Republic of Korea. A hypothetical accident was assumed for Shin Kori unit 3 to perform the time-dependent dose calculations along with the release rates of radionuclides to the environment. In order to assess the accident scenarios, Radiological Assessment System for Consequence Analysis code was used, which is a set of tools for emergency response applications developed by US Nuclear Regulatory Commission. A straight-line Gaussian model was used for the near-field atmospheric calculations and a Lagrangian Gaussian puff model was used for the far-field simulations where released radioactive materials to the environment were transported, dispersed and deposited. In this study, long-term station blackout in spring, summer, autumn and winter season was considered in 2016–2018 based on reactor condition and seasonal effects. It was found that the worst season is the spring and the worst scenario found during the evening time of spring in 2017. The calculated maximum values of total effective dose equivalent (TEDE) and thyroid committed dose equivalent (CDE) are 22 mSv and 390 mSv, respectively, around 5 km of precautionary action zone (PAZ) in 2 days after the accident. According to Korean regulations on urgent public protective actions, for indoor sheltering, the criteria are 10 mSv in 2 days. For public evacuation 50 mSv in 1 week and iodine prophylaxis should be introduced if thyroid protection level is 100 mSv. Calculated values of TEDE are more than double and thyroid CDE is almost four times in the PAZ compared with Korean regulations; hence, it was found that indoor sheltering and supply of iodine prophylaxis should be executed for short/mid-term protective measures. In this situation, indoor sheltering should be decided by off-site emergency management center, which was accountable for emergency decision-making process in nuclear accident under nuclear safety and security commission in Korea.