Nuclear Power Corporation of India Limited (NPCIL) has engaged Mumbai-based EPC contractor CORE Energy Systems to replace the primary recirculation piping at units 1&2 of the Tarapur Atomic Power Plant (TAPS) in Palghar district, in Maharashtra state. The refurbishment should extend plant life by 10 years.

TAPS, was India’s first commercial NPP, constructed initially with two boiling water reactors (BWRs) which began commercial operation in 1969 with an initial power of 210 MWe of electricity. Later this was reduced to 160 MWe due to technical difficulties. Subsequently two 540 MWe pressurised heavy water reactor (PHWR) units began operation at the site in 2005 and 2006.

The project aims to address the significant safety concerns associated with Intergranular Stress Corrosion Cracking (IGSCC) in the piping of the primary circuit and other class-1 piping. IGSCC is a phenomena of stress corrosion cracking that can occur along the grain boundaries of the heat affected zone of austenitic steel welds or the cold worked zone. Following the necessary regulatory approvals, NPCIL chose to replace these critical components.

Subsequently, the contract for the complete replacement of the primary recirculation piping was awarded to CORE Energy Systems, which was the most competitive technically qualified contractor. The project presents significant challenges such as working in the radioactive zone, complex cutting engineering, disposal of the existing piping and replacement with pipes of highly specialised material.

The new forged pipes and fittings are being manufactured conforming to ASME SA 312 SS 316 LN with stringent chemistry and dimensional control. The entire reactor building interiors have been scanned using high precision 3D scanning technology, and a full-scale mock-up structure has been built to represent the reactor building environment.

The radiation exposure to the workmen has been minimised to a large extent by the usage of automated orbital cutting and orbital welding machines and radiation shielding measures. CORE had to devise various special systems including for decontamination, safe end shielding plugs, insertion mechanism, and position monitoring.

Image: Tarapur Atomic Power Plant in Palghar district, Maharashtra state (courtesy of NPCIL)