Examination of Leaking Tube-to-Tube-Plate Welds from an Austenitic Steel Steam Generator Superheater in the Dounreay Prototype Fast Reactor

During commissioning of the Dounreay prototype fast reactor steam generators in 1974, a steam-to-sodium leak occurred in the tube-to-tube-plate weld area in one of three superheaters. This caused caustic stress corrosion of the tube plate in the areas exposed to the products of the sodium-water reaction. Metallurgical examination of several welds revealed one manufacturing defect, which was due to reheat cracking. This was the likely cause of the initial steam-to-sodium leak that resulted in failure in several adjacent tubes due to caustic stress corrosion cracking. The holes in the tube plate where the welds had been cut out for examination were plugged by explosive welding techniques and the unit returned to service.