Metallurgical Examination of Tube-to-Tube-Plate Welds Removed from Dounreay Prototype Fast Reactor Evaporators

A number of welds in the evaporators of the prototype fast reactor have failed during service. Two types of cracking have been observed, namely longitudinal from the bore and circumferential from the outside. The circumferential cracks are believed to have been caused by stress corrosion resulting from caustic contamination that arose early in the operational life. The reason for the initiation of the longitudinal cracks appears to be stress corrosion cracking on the water side.