After the Fukushima nuclear accident in Japan, concerns have increased about radioactive releases from nuclear power plants (NPPs) into the environment. Analysis of annual radioactive effluent release reports (ARERRs) shows that from 2000 to 2020, abnormal releases of radioactive effluent occurred in 703 out of 1,323 Reactor·years in the United States, accounting for 53% of the total number of reactors in 63 PWRs. Furthermore, when examining incidents and malfunctions recorded in Korea’s Operational Performance Information System of Nuclear Power Plant (OPIS) during the same period, it can be estimated that abnormal releases occurred in 9 out of the 324 Reactor·years in PWRs and PHWRs. Meanwhile, database on radioactive releases from NPPs worldwide was collected, and events of abnormal/unplanned releases were investigated. Based on the data collected from 195 NPPs in 8 countries (South Korea, the United States, Japan, France, the United Kingdom, Germany, Spain, and Canada) over a period of 21 years, totaling 4,607 Reactor·years, a program called K-IRED (KHUIntegrated Radioactive Effluent Database) was developed using MS Access. Using K-IRED, three methodologies have been developed to predict abnormal events based on the annual radioactive releases for each NPPs and radionuclide (or radionuclide group). Three newly developed methodologies were applied to the 63 NPPs (1,323 Reactor·years) in the United States, categorized by radionuclides (or radionuclide groups). Assuming an increase in radioactive effluent due to abnormal events, the annual increase rate of radioactive effluent was calculated for each methodology and the results were analyzed. The optimal methodology among the three was derived, and the applicability of predicting abnormal events in other NPPs beforehand was examined. Therefore, by predicting abnormal or unplanned releases from NPPs to the environment in advance, it is possible to prevent accidents and reduce public concerns, as suggested by results of this study.

In case of Korea, unlike overseas nuclear power plants, adjacent units are located in permanently stopped nuclear power plants. Radioactive substances from airborne and liquid effluents are released into the environment from the NPP, and the radioactivity of the released substances must be reported to the regulatory authorities. Radioactive effluents are released into the environment not only in operation but also after permanent shutdown. Due to domestic conditions in which multiple units exist on the same site, it is necessary to consider radioactive effluents generated after permanent shutdown of NPPs. In particular, liquid effluent may have an increased tritium concentration due to draining the spent fuel pool. This paper summarizes the annual liquid emissions of PWR power plants that have been permanently shut down. The data was obtained from the Nuclear Regulatory Commission’s (NRC) annual radioactive effluent release report, which provides information on the annual emissions power plants into the environment. The liquid emissions of each plant were organized into an annual table, providing an overview of the amount of liquid released by each plant. This study aims to raise awareness about the potential environmental impact of permanently shut down nuclear power plants and the need for proper management of their liquid emissions. The findings of this study can used by operator, policymakers, and other stakeholders to make informed decisions regarding the decommissioning and management of nuclear power plants.