Technological development toward nuclear reactor decommissioning. Utilization of 3D measurement data (6D CAD™) and system decontamination (T-OZON™)

Toshiba Corporation has been developing the technologies related to decommissioning for more than 30 years, and making them into practical use. This paper introduced 6D CAD™, which applies the CAD system that is effective for rational planning at the initial stage and effective for managing the progress of construction work, as well as T-OZON™ method, which is effective for reducing the exposure of construction workers. This 6D CAD™ can deal with the following items necessary for decommissioning work: (1) decommissioning management such as schedule control and yearly exposure dose management, (2) management such as planning and implementation of procedures, as well as waste management and traceability, and (3) essential technologies such as the optimization of dismantling plan, reduction in processing/disposal cost, database construction for engineering information, measurement of reactor inside, and measurement of radiation dose and database construction of its information. T-OZON™ method is a chemical decontamination technology that can be applied to pre-demolition decontamination aimed at reducing the exposure of workers and reducing the amount of radioactive materials in the dust generated during dismantling work, and greatly reducing the secondary waste originated from used chemicals. Oxalic acid is used as a reducing agent, and ozone water is used as an oxidizing agent. This method has been applied over 200 times mainly for BWR. The application to PWR has been tested by experiments, and prospects for achieving the target value for decontamination have been obtained for both materials of SUS 304 and Alloy 600. (A.O.)