Application of Laser-Manufacturing Technology to Fabricate Square Tubes for Multi-Purpose Canister

The UMS/MPC transport/storage system developed by NAC International consists of a multi-purpose canister that is called the Transportable Storage Canister, which holds spent fuel in an orderly manner to maintain sub-criticality, and a concrete over-pack for storage. The multi-purpose canister consists of a basket, a thin wall container shell and a double lid system. The basket consists of thin wall square tubes, and support and heat transfer disks. The components required highly accurate fabrication to obtain a high-density fuel assembly payload. In the US, several nuclear power stations have been under decommissioning programs and a large quantity of storage systems are required at one time to move the spent fuels from an existing storage pool to an above ground storage pad at the nuclear power station. As the canisters contain 30 to 40 fuel assemblies, and 40-50 canisters are necessary for one project, more than one thousand square tubes must be fabricated.. To cope with this demand for large quantities of tubes in a short period of time and severe tolerances, laser beam welding technology has been developed and applied to fabricate a large number of thin wall square tubes. The development and application of the laser beam welding technology to the fabrication of a thin wall square tube is explained in this report. The square tube is made of thin wall stainless steel plate and has a double paneled structure of the tube body and cover for the neutron absorbing material. The tube body is obtained by welding two C shaped stainless steel plates with a butt joint welds, and the neutron cover is fitted to the four sides of the tube by a continuous fillet joint weld. Using laser technology, multi-purpose canisters, which satisfy all design requirements, are achieved.