Identificatio of Leaky Steam Generators by Iodine Mapping Technique and Development of Tools for Cutting of Tubes of Steam Generators of Indian PHWRs

Steam generators (SG) are a very important component of a nuclear power plant (NPP), as they are part of the primary heat transport (PHT) system of pressurized heavy water reactors (PHWRs). Kakrapar Atomic Power Station (KAPS) is of 2 × 220 MWe and has four mushroom-type steam generators, each consisting of 1834 U-tubes (16-mm 00 and 1-mm wall thickness) made of Incoloy-800 material. The tubes of ‘tube-and shell-type steam generator‘ act as the pressure boundary of the PHT system. Any structural failure of these tubes can lead to a release of radioactivity along with plant outage and heavy economic loss. A technique was developed by chemical laboratory to identify the SG having leaky tUbe using lodine-134 and a special cutting and the removal tools were developed by mechanical maintenance unit (MMU) of KAPS. Both the primary and the secondary sides of the steam generators are designed and manufactured as per the requirements of class-I components in section-III of the ASME boiler and pressure vessel code.