In South Korea, the replacement of steam generators began with Kori Unit 1 in 1995, and to date, 20 steam generators have been replaced and are currently stored in intermediate storage facilities. In the future, additional decommissioned steam generators may arise due to measures like the extension of the lifespan of nuclear power plants. In Korea, technological development for dismantling steam generators is underway, and there is no track record of actual dismantling. Although the replaced decommissioned steam generators are stored in intermediate facilities, for site recycling purposes, steam generators, which have relatively lower radiation doses compared to reactor heads and other primary equipment, should be prioritized for dismantling. While there are various specifications for steam generators, those dismantled and stored domestically are of the Recirculation Type. They can be classified into three types: the Westinghouse type WH-51 used in Kori Unit 1, the Fra-51B used in Han-ul Units 1 and 2, and the OPR-1000 used in Han-ul Units 3 and 4. The quantity of U-Tubes varies depending on the specification, but the radiation is concentrated in the primary side components, the U-Tube and Chamber. Since the parts related to the secondary side are not contaminated, they can be disposed of independently after classification. To dismantle a steam generator, it is of utmost importance to first create a scenario regarding where and how the dismantling will take place. Through the analysis of the advantages and disadvantages of each scenario, the optimal timing, location, and cutting method for dismantling should be researched. Furthermore, based on those findings, the best scenario should be derived through an analysis of worker radiation exposure and dismantling costs. To achieve this, a 3D simulation software developed by Cyclelife Digital Solutions under the French EDF was utilized to conduct simulations based on different dismantling schedules and methods. As a result, the optimal scenario for dismantling the steam generator was derived.

The personal exposures of nitrogen dioxide(NO2), microenvironmental levels and daily time activity patterns on Seoul subway station workers were measured from February 10 to March 12, 1999. Personal NO2 exposure for 24 hours were 29.40±9.75 ppb. NO2 level of occupational environment were 27.87±7.15 ppb in office, 33.60±8.64 ppb in platform and 50.13±13.04 ppb in outdoor. Personal exposure time of subway station workers was constituted as survey results with 7.94±3.00 hours in office, 2.82±1.63 hours in platform and 1 hours in outdoor. With above results, personal NO2 exposure distributions on subway station workers in Seoul were estimated with Monte Carlo simulation which uses statistical probabilistic theory on various exposure scenario testing. Some of distributions which did not have any formal patterns were assumed as custom distribution type. Estimated personal occupational NO2 exposure using time weighted average (TWA) model was 31.29±5.57 ppb, which were under Annual Ambient Standard (50 ppb) of Korea. Though arithmetic means of measured personal NO2 exposure was lower than that of occupational NO2 exposure estimated by TWA model, considering probability distribution type simulated, probability distribution of measured personal NO2 exposures for 24 hours was over ambient standard with 3.23%, which was higher than those of occupational exposure (0.02%). Further research is needed for reducing these 24 hour NO2 personal excess exposures besides occupational exposure on subway station workers in Seoul.