Chemical Decontamination for Decommissioning (DFD) and DFDX

DFD is an acronym for the “Decontamination for Decommissioning” process developed in 1996 by the Electric Power Research Institute (EPRI). The process was designed to remove radioactivity from the surfaces of metallic components to allow these components to be recycled or free-released for disposal as non-radioactive. DFD is a cyclic process consisting of fluoroboric acid, potassium permanganate and oxalic acid. The process continues to uniformly remove base metal once oxide dissolution is complete. The DFD process has been applied on numerous components, sub-systems and systems including the reactor systems at Big Rock Point and Maine Yankee in the United States, and the Jose Cabrera (Zorita) Nuclear Power Plant (NPP) in Spain. The Big Rock Point site has been returned to Greenfield and at Maine Yankee the land under the license was reduced for an Independent Spent Fuel Storage Installation (ISFSI). In the upcoming months the Zorita NPP in Spain will initiate dismantlement and decommissioning activities to return the site to a non-nuclear facility. The development of the EPRI DFD process has been an ongoing evolution and much has been learned from its use in the past. It is effective in attaining very high decontamination factors; however, DFD also produces secondary waste in the form of ion exchange resins. This secondary waste generation adds to the decommissioning quota but this can be improved upon at a time when radioactive waste storage at nuclear facilities and waste disposal sites is limited. To reduce the amount of secondary waste, EPRI has developed the DFDX process. This new process is an enhancement to the DFD process and produces a smaller amount of metallic waste rather than resin waste; this reduction in volume being a factor of ten or greater. Electrochemical ion exchange cells are the heart of the DFDX system and contain electrodes and cation ion exchange resin. It has been used very successfully in small system applications and the next evolution is to design, build and implement a system for the chemical decontamination for decommissioning of larger reactor systems and components, and Full System Decontamination (FSD). The purpose of this paper is to provide a reference point for those planning future chemical decontaminations for plant decommissioning. It is based on actual experience from the work already performed to date and the planned development of the DFDX process.