[en] KSC-4 transport cask and handling equipment should be safely stored and managed in the radiation controlled area. Therefore, it is necessary to approve the change of the PIEF’s warehouse to a radioactive waste storage facility. The purpose of this study is to obtain approval for change of license to the radioactive waste storage facility and to derive a plan for decontamination and decommissioning of KSC-4 cask. Basic data for decontamination and decommissioning of the transport cask were obtained by analyzing the decontamination and decommissioning technology for the spent fuel transport cask and nuclear facilities. The storage, decommissioning status and recyclability of unused cask were analyzed, and future treatment plan and recyclability of transport cask was suggested. The amount of radioactivity of the transport cask was predicted based on the results of measuring the internal radiation dose rate and contamination level of the KSC-4 cask. An analysis of the gas sampling method of the transport cask was performed and the concept of a gas sampling equipment was derived. An application for change of license has been submitted to the authority to convert PIEF’s warehouse into a radioactive waste storage facility. In addition, Q&A was conducted for two times of licensing review. After obtaining the change of license for the existing RG laboratory, the moving and installation of the equipment was completed, and applications for change of license the RI/NM laboratory were prepared. The results obtained from this study will be available as basic data for change of license to a radioactive idle equipment storage facility and decontamination & decommissioning of the KSC-4 cask