Lessons learnt from double ended rupture of 10 % feed water line to steam generator in Kakrapar Atomic Power Station-2

Ensuring safe, reliable operation of Secondary Cycle System in Nuclear Power Plant (NPP) is very important not only from power generation point of view but also from the industrial safety concerns. Secondary cycle comprises of various high energy systems such as Main Steam, Boiler feed water, Boiler blow down and Steam drains etc. Failure of any of the pipes and fittings pertaining high energy systems piping can result in complex challenges to the operating staff and plant. Most of the secondary cycle systems are housed in the turbine building and it is routine for the workers to enter this building for daily walk around checks and other purposes. It is important to not only prevent the radiation hazards but also prevent industrial accidents at Nuclear Power Plants. There was a pipe rupture on 9th August 2004 at Mihama Unit - 3 (Japan) 826 MWe of condensate line between feed water heater No.4 and deaerator in the Turbine Building. Similar kind of a pipe rupture occurred at Kakrapar Atomic Power Station (KAPS) Unit-2 on 9th Feb, 2006 on the 10 % feed water line to Steam Generator (SG) releasing steam to boiler room. Both these failures were assessed to be because of flow assisted corrosion (FAC). Subsequent to above incidents lot of efforts had been put to prevent similar incidence of piping failures in high energy systems of Indian NPPs on account of FAC. This paper brings out measures to overcome flow assisted corrosion (FAC) and monitoring program adopted in Indian NPPs to combat failures in Secondary Cycle Piping on account of FAC. (author)