KANUPP operation with four out of six steam generators

This paper highlights the experience at Karachi Nuclear Power Plant of operation with 4 out of 6 steam generators in service. Removal of two steam generators, one from each loop of the normal circuit, was necessitated due to the development of leak in one of the steam generators. The normal approach of leak search, plugging of tube and, subsequent ISI of steam generator could not be attempted mainly because of lack of tools, expertise, and experience in the relevant field. Suitable modifications were, however, carried out to isolate the faulty steam generator from the circuit and restart the plant with 4 steam generators instead of 6. The primary pumps in operation were also reduced from 3 pairs to 2 pairs. The modifications required a series of studies, analyses and changes to piping work in the steam boiler feed water circuit. Comprehensive stress analysis was carried out to make sure that steam and PHT headers can withstand the uneven expansion of hot and cold pipings steam generators. The plant rating was reduced to ensure that design criteria are not violated with the new configuration. Various trip limits and set points were adjusted accordingly. A number of special commissioning tests were done to validate the theoretical predictions. Finally the Plant was restarted and connected to the grid on Jan. 03, 1991 and loaded to 50 MWe (45% R.P). The present modified mode of operation is considered temporary and all efforts and resources, both indigenous and international, are being mobilized to carry out leak search, ISI, plugging the leaking tube and restoring the plant to normal configuration for high power operation. (author)