<p>This study developed a comprehensive safety assessment model implemented in Microsoft^® Excel for the multi-stage processing of decommissioning waste. The model enhances existing approaches by allowing flexible combinations and sequencing of processing steps while considering material transformations such as phase separation during melting and incineration. It integrates the International Atomic Energy Agency Safety Reports Series No. 19 for small facilities and a module based on United States Nuclear Regulatory Commission Regulatory Guide 1.109 for large facilities to support age-specific public dose assessments. Partial verification of the public dose assessment module using NRCDose3 Code version 1.1.4 confirmed its accuracy and reliability. The model was tested at the comprehensive radioactive waste processing facility within the Kori nuclear power plant site and incorporated various waste types and processing steps including melting and incineration. Assessment accounted for phase changes and nuclide redistribution during processing. External exposure from ⁶⁰Co and ¹³⁷Cs was dominant for most workers under normal conditions, while ⁵⁴Mn exposure was significant for slag workers due to radionuclide partitioning. In abnormal conditions, inhalation became the major exposure pathway for workers and the public. This model offers a robust framework for evaluating radiological impacts in decommissioning waste processing to ensure enhanced protection for workers and the public.</p>