CORE Energy Systems leads life extension of the Tarapur nuclear plant

25 April 2024

Nuclear Power Corporation of India Limited has embarked on a first-of-its-kind endeavour for replacement of primary recirculation piping at units 1 and 2 of the Tarapur Atomic Power Plant (TAPS).

Units 1 and 2 of the Tarapur plant (Image: NPCIL)

This unprecedented project aims to revitalise India's inaugural nuclear power facility, which commenced operations in 1969. With the aim of setting a precedent for technical innovation in engineering and contributing to the nation's growth, Nuclear Power Corporation of India Limited (NPCIL) has entrusted the works to CORE Energy Systems Limited, a Mumbai-based EPC contractor specialising in such technologically niche projects.

The project addresses the significant safety concerns associated with Intergranular Stress Corrosion Cracking (IGSCC) in the existing piping of SS 316L material, which comprises of the primary recirculation piping and other class-1 piping, a phenomenon notably prevalent in aging boiling water reactor (BWR) plants globally. 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 proactively chose to replace these critical components, thereby revitalising the plant and significantly enhancing its safety.

The initiative to replace the primary recirculation and other class-1 piping systems, made primarily of SS 316L material, was a proactive response to address the significant safety concerns associated with IGSCC. The phenomenon is typically observed along the grain boundaries in the heat-affected zones of austenitic steel welds or cold-worked zones, particularly prevalent in BWR plants worldwide.

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 entailed steep challenges such as working in the radioactive zone, detailed engineering of cutting, disposal of the existing piping and replacement with pipes of highly specialised material.

CORE's Chairman and Managing Director Nagesh Basarkar stated that the project challenges are being tackled well through CORE's technical expertise and well-established global sourcing network for such highly technological components in the nuclear industry.

The forged pipes and fittings to be used for the replacement work 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, while a 1:1 scale mock-up structure has been erected to recreate the reactor building environment. Most of the planning and training activities are being undertaken using these innovative aids.

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. The project has also needed CORE to develop ingenious systems for decontamination, safe end shielding plugs and insertion mechanism, position monitoring system and many more.

CORE said such innovations reflect its commitment towards Prime Minister Modi's 'Make-in-India' programme and the Government of India's push to develop indigenous technologies.

"We anticipate a successful completion of this project as per the planned schedule and are confident that the refurbishment will extend the Tarapur power plant's lifespan by a decade," said a CORE spokesperson.

CORE said it embarks on this refurbishment project "with a vision to pioneer further advancements in the life extension of aging nuclear power plants, underpinning our commitment to nuclear energy as a cornerstone of renewable resources. By revitalising these critical assets, we aim to make a contribution to India's nuclear power sector, thereby supporting the country's ambitious goal of achieving net-zero emissions by 2070. Our efforts signify a strategic alignment with national energy policies, emphasising our role in enhancing the sustainability and reliability of India's energy infrastructure."

Commissioned in 1969, the Tarapur plant, which is in the Palghar district of Maharashtra state, was the first commercial nuclear power plant in India. It consists of units 1 and 2, with each unit having a 160 MWe (gross) boiling water reactor, and both have been operational since the plant’s inception. Subsequently, two pressurised heavy water reactors, each of 540 MWe (gross), were added at the Tarapur site as units 3 and 4.

Researched and written by World Nuclear News