Steam generators life extension experience at KANUPP

Karachi Nuclear Power Plant (KANUPP) commissioned in 1972 has been operating under PLEX since Jan 2004, after completion of 30 years of its design life. It is planned to extend its life at least by another 15 years after necessary upgrades and re-licensing outages (RLO) by local regulators. KANUPP has six steam generators (SGs), with half-inch diameter Monel-400 tubes. In-service inspection is being carried out regularly in compliance with plant and regulatory requirements (CSA N285.4 for tubes and ASME codes for shell and internals). Degradation is prominent in tubes under sludge from pitting/wastage and denting at first tube support plate (Corten steel) in all the six SG units. Up til now there has been only one instance of a tube leakage and so far 99 tubes (i.e. 1.2% of the total tubes) have been plugged based on wall thinning and severely dented at first tube support plate. A regular monitoring program that is in place includes inspection of tubes, primary and secondary internals, shell, supports and connection welds. Plugging criteria for tubes is ≥ 40% for wall thinning and ≤ 0.250 inch opening for denting using stabilizer bars. An extensive monitoring program for condition assessment is in hand to keep a watch on the rate and morphology of degradation mechanisms and surveillance on susceptible areas unless remedial and control measures are effectively in place. KANUPP steam generators have so far undergone partial water lancing in 2000, hydraulic analysis study, mechanical integrity and comprehensive inspection of tube, overall condition assessment, internals, shell welds and supports inspection. (author)