ALARA-based assessment of reactor vessel head dismantling using 3D simulation: Worker dose, cost, and time evaluation

This study aims to establish an optimized decommissioning strategy for radiation protection by quantitatively evaluating worker radiation dose and decommissioning costs for the dismantling of a reactor vessel head (RVH). A three-dimensional model was developed based on the actual geometry of the Kori Unit 1 RVH, and various decommissioning scenarios were analyzed using the DEMplus simulation tool, considering factors such as decontamination, cutting methods, decommissioning timing, and the application of remote cutting. In the baseline scenario with manual cutting at 10 years after replacement, individual dose was 45.38 mSv, exceeding the operator's internal limit of 20 mSv per year. Replacing manual cutting with remote robotic cutting reduced the collective dose by approximately 95.9%, with the individual dose decreasing to 1.66 mSv. Although delaying dismantling by 15 or 20 years produced additional dose reduction due to radioactive decay, its economic benefit was limited when accounting for long-term storage costs. Strengthening decontamination procedures showed varying effectiveness depending on the cutting method. This study provides an optimized execution strategy by comprehensively evaluating dose, cost, and work time across scenarios, offering practical reference data to support radiation protection and decision-making in future RVH decommissioning projects.