Abstract
Assessing workers’ safety and health during the decommissioning of nuclear power plants (NPPs) is an important procedure in terms of occupational radiation exposure (ORE). Optimizing the radiation exposure through the “As Low As Reasonably Achievable (ALARA)” principle is a very important procedure in the phase of nuclear decommissioning. Using the VISIPLAN 3D ALARA planning tool, this study aimed at assessing the radiological doses to workers during the dismantling of the reactor pressure vessel (RPV) at Kori NPP unit 1. Fragmentation and segmentation cutting processes were applied to cut the primary component. Using a simulation function in VISIPLAN, the external exposure doses were calculated for each work operation. Fragmentation involved 18 operations, whereas segmentation comprised 32 operations for each fragment. Six operations were additionally performed for both hot and cold legs of the RPV. The operations were conducted based on the radioactive waste drum’s dimensions. The results in this study indicated that the collective doses decreased as the components were cut into smaller segments. The fragmentation process showed a relatively higher collective dose compared to the segmentation operation. The active part of the RPV significantly contributed to the exposure dose and thus the shielding of workers and reduced working hours need to be considered. It was found that 60Co contained in the stainless steel of the reactor vessel greatly contributed to the dose as an activation material. The sensitivity analysis, which was conducted for different cutting methods, showed that laser cutting took a much longer time than plasma cutting and contributed higher doses to the workers. This study will be helpful in carrying out the occupational safety and health management of decommissioning workers at Kori NPP unit 1 in the near future.
Highlights
Kori unit 1, a two-loop Westinghouse pressurized light water reactor with an output of 587 MWe, was the first Korean commercial nuclear power plant (NPP) and started its operation in April, 1978 and was permanently shut down for decommissioning in June, 2017
The top two fragments were cut into 32 segments, while the remaining two smaller fragments were cut into 10 segments
The values predicted in this study were relatively higher since we focused on the reactor pressure vessel (RPV), which was a primary component of the NPP, and strict measures, such as reduced time and increased shielding should be taken to protect decommissioning workers and keep the radiation exposure to the workers as low as possible
Summary
Kori unit 1, a two-loop Westinghouse pressurized light water reactor with an output of 587 MWe, was the first Korean commercial nuclear power plant (NPP) and started its operation in April, 1978 and was permanently shut down for decommissioning in June, 2017. The nuclear decommissioning of Kori unit 1 was scheduled to last for at least 15 years; the cooling of spent nuclear fuel in 2017–2022, decontamination and dismantling in 2022–2028, and site restoration by 2032 [1,2]. Several activities, including the preparation of a final decommissioning plan (FDP) which should be submitted to the regulator within 5 years after permanent shutdown, i.e., by June, 2022, public hearings with residents near Kori NPP unit 1 for year, the completion of spent nuclear fuel transfer by 2025, the decontamination and dismantling of structures, systems and components (SSCs) of Kori unit 1, the treatment and conditioning of radioactive. Public Health 2020, 17, 5346; doi:10.3390/ijerph17155346 www.mdpi.com/journal/ijerph
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