Evolution of the design of the engineered barrier system for the long term management of CANDU® fuel

The Nuclear Waste Management Organization (NWMO) is responsible for the implementation of Adaptive Phased Management (APM), the federally-approved plan for the safe long-term management of Canada's used nuclear fuel. Under the APM plan, used nuclear fuel will ultimately be placed within a deep geological repository in a suitable rock formation. Consistent with technology advancements, the engineered barrier design has evolved, but the original technical solution defined in the late 1980s remains the preferred technical solution; containerization of used nuclear fuel into long lived metallic containers encased in bentonite with the engineered barrier isolated from the biosphere in an engineered structure deep underground. The current evolution of the Used Fuel Container (UFC) engineered barrier utilizes commercial steel pipe with spherical heads. Hybrid laser arc welding affixes the heads to the pipe. The entire UFC is copper coated, prior to loading and final assembly; excepting a small width required to permit welding of the final head after all fuel is loaded. Cold spray is used to apply the copper coating over the weld area. The final assembled UFC is placed in a highly compacted bentonite block, assembled from two pressed blocks forming a rectangular package transferred underground. It is placed in an emplacement room using slip skid technology to deposit the assembly in a one wide by two high assembly arrangement. Highly compacted bentonite spacer blocks provide the require assembly offset to control peak UFC surface temperature. Each room is filled in a retreating manner. (author)