Managing stress corrosion cracking in nuclear turbine rotors

A large U.S. nuclear utility recently was faced with a severe, life limiting, Stress Corrosion Cracking (SCC) situation on the Low Pressure (LP) turbine rotors of its dual 1127 MWe unit PWR nuclear plant. Although the ultimate decision was made to replace the six damaged rotors with modern equipment, significant life extension was achieved on the old equipment in a very short period of time. This experience should be of interest to owners of nuclear units around the world due to the wide spread nature of SCC in LP turbine rotors. The lessons learned in life extension are of particular value because innovative techniques were employed with tremendous success. The decision to replant the units was made following preparation of a strategic plan that evaluated the economics of all the options available. This study concluded that today's' significantly improved, industry wide, design and construction technology offered not only much improved life and hence reliability but an impressive increase in efficiency and thus electrical output. This paper discusses the utility's approach and philosophy from discovery of the SCC problem, through the interim repair process, economic study, preparation of equipment specification, selection of successful design and supplier, procurement of the new equipment, through detailed review of the selected replant vendor's completed design. (authors)