The Nuclear Waste Management Organization (NWMO) is implementing the Adaptive Phased Management program since 2007 for the long-term management of Canada’s used nuclear fuel. The end point of this program is to contain and isolate the used fuel in a centralized Deep Geological Repository (DGR). The DGR is composed of a multiple barrier system that includes a suitable rock formation and several engineered barriers. A key component of the engineered barrier system is the Used Fuel Container (UFC). This is the containment vessel in which used fuel will be packaged. The current reference UFC design (i.e., the Mark II design) is a small sized cylindrical container with hemispherical heads. The container is made of carbon steel with a copper coating applied to the external surface for corrosion protection. This unique design is driven by the optimal long-term performance under the repository conditions and the characteristics of the natural uranium CANDU fuel, which represents the majority of the used fuel inventory in Canada. The development of the design involves many years of work in all fronts of the subject, including corrosion and material degradation, structural integrity, manufacturing processes, inspection and testing.

This paper focuses on the structural design of the UFC at the NWMO. The main challenges in the design of disposal containers are reviewed, followed by the examination of the applicability of existing codes and standards, such as the ASME BPVC. Then the developments of the container design methodology, criteria and constraints are discussed. The impact and dependency of the container design activities on other aspects of the project, e.g., container manufacturing and inspection, safety assessment, geoscience investigations and facility operations, are also briefly discussed. Finally, the design verification and validation testing programs, including the full scale external pressure tests, are presented.

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