Development of a Flexible and Robust Patch Weld for Dry Nuclear Storage Casks

Dry waste Nuclear storage casks were initially designed as a short term storage solution between the spent rod cooling pools and permanent storage. However, with the demise of long term storage solutions, such as Yucca Mountain, the lifetime of these casks has now become indefinite. The concern is that each cask contains enough highly toxic, long half-live radioactive isotopes, so that a cask failure would poison large swaths of land, which include rich agricultural and population centers. Due to the construction of the casks, the weld joints are not directly inspectable, and the high radiation and temperature environment allow only robotic repairs. With the possibility of stress-corrosion cracking in these joints, a means to inspect and repair cracks remotely is of paramount importance. SCT has pioneered the use of Ti and Ni powders to effect a welded joint in TiNi, Ti, CoCr and stainless steels. The technique relies on packing the Ni and Ti metal powders into the crack. The packed powders are reacted locally, and as the reaction spreads, local temperatures within the powder exceed 1400 oC, alloying the TiNi product with the crack surface. The reaction typically lasts 1 to 5 seconds, depending on the volume of the powder, which means that the welded area is surgically precise, with no heat affected regions outside of the crack. In phase 1, we will evaluate the strength of the weld from the TiNi to the stainless steel cask material under a variety of process conditions, using mechanical testing and microscopy to characterize the weld interface. This concept is a radical departure from conventional welding techniques, but it offers a surgically precise weld with minimal impact to the key structural welds joining the cask walls, which must be an absolute importance given the consequence of a cask wall breach.A catastrophic weld failure on any one of the 2200 dry casks will be catastrophic to the local area surrounding the 75 sites in the US, most of which are near heavily populated areas. Securing these casks via the proposed inspection and repair technique will safeguard the population. As the number of casks in increasing by about 200 per year, inspection and repair will become a $30M industry with 5 years of NRC and customer acceptance.