Kaiga Unit-1 completes core reactor overhaul and loads fresh nuclear fuel

India’s nuclear power sector achieved an important engineering milestone on September 13, 2026, as Nuclear Power Corporation of India Limited (NPCIL) successfully loaded the first fresh nuclear fuel bundle into Unit-1 of the Kaiga Generating Station (KGS-1). This event marks the completion of the complex En-Mass Coolant Channel Replacement (EMCCR) and En-Mass Feeder Replacement (EMFR) refurbishment campaign. Located in the Karwar district of Karnataka, the 220 MWe Pressurised Heavy Water Reactor (PHWR) has now entered final restart activities following a major mid-life overhaul. Executing this core reactor replacement in record time highlights the growing capability, speed, and technical precision of India’s domestic nuclear engineering ecosystem.

KGS-1 was shut down for this lifecycle refurbishment on April 1, 2025, after delivering more than 25 years of safe commercial operation. Prior to its temporary shutdown, the reactor had generated approximately 37,670 Million Units (MU) of clean electricity for the national grid. Operating in a demanding environment of intense neutron flux, elevated temperatures, and high fluid pressures over two decades causes structural evolution in core materials. In PHWR technology, heavy water serves as both coolant and moderator, flowing through horizontal pressure tubes within a calandria vault. Over long operating campaigns, zirconium-alloy pressure tubes and carbon steel feeder lines experience irradiation-induced creep, axial growth, and material embrittlement. Replacing these core components restores original design safety margins and enables the reactor to operate reliably for an additional 25 to 30 years.

Technical Mechanics of EMCCR and EMFR Core Refurbishment

The overhaul of a Pressurised Heavy Water Reactor is among the most intricate mechanical engineering challenges in the power sector. A 220 MWe PHWR core contains hundreds of horizontal coolant channels connected to intricate network arrays of feeder pipes that circulate heavy water coolant to steam generators. The EMCCR and EMFR campaign requires a rigidly sequenced progression of mechanical cutting, metrological inspection, and precision welding under radiological containment protocols. Operations began with complete reactor defueling and heavy-water recovery from the primary heat transport loop to manage tritium safety.

Automated cutting equipment and specialized remote tools were then deployed inside the vault to sever and extract the aged zirconium-niobium pressure tubes, calandria tubes, and stainless steel end-fittings. Simultaneously, teams removed hundreds of incoming and outgoing feeder pipe runs. Following component extraction, engineers conducted comprehensive non-destructive evaluations and optical metrology inside the calandria vault to inspect alignment, internal geometry, and support structures. Re-assembly involved installing new zirconium-niobium pressure tubes, repositioning garter spring spacers, and fitting new feeder pipe runs. Every joint and weld underwent rigorous ultrasonic, radiographic, and dimensional inspection to satisfy strict nuclear quality assurance standards.

Record Execution Speed and Indigenous Supply Chain Strength

A notable highlight of the KGS-1 refurbishment is that NPCIL achieved the EMCCR and EMFR completion in the shortest timeframe ever recorded across all Indian PHWR units undergoing major reactor overhauls. Historically, reactor channel replacement programs required prolonged outages due to the hazardous, radiation-intense environment and the technical complexity of remote alignment inside reactor vaults. The record turnaround at Kaiga Unit-1 reflects decades of incremental refinement in tooling design, automated control systems, pre-outage mock-up simulations, and standardized execution protocols.

This achievement underscores the mature self-reliance of India’s nuclear supply chain. Domestic heavy engineering firms, component manufacturers, and tooling developers now produce forged end shields, precision-machined coolant channel assemblies, seamless feeder pipes, and specialized alignment rigs entirely within the country under stringent nuclear codes. By mastering the full spectrum of reactor maintenance—from automated tube cutting to in-core laser metrology—the Indian nuclear sector has established global benchmarks in PHWR life-extension engineering.

Primary Circuit Pressure Validation, Hydrotesting, and Hot Conditioning

Following the fuel loading milestone on September 13, 2026, KGS-1 transitioned from structural assembly to thermo-hydraulic testing and fluid system validation. Before approaching nuclear criticality and initiating power generation, the primary heat transport loop must undergo rigorous physical and chemical commissioning protocols to guarantee pressure boundary integrity.

Initial post-refurbishment testing involves helium leak detection across all newly welded feeder joints and mechanical seals to confirm micro-scale tightness. Once verified, the primary circuit is charged with heavy water and subjected to hydrostatic pressure testing. Hydrotest rigs pressurize the primary circuit significantly above its normal operating pressure baseline of approximately 8.7 MPa using ambient-temperature fluid. This test validates the mechanical strength of new welds, pipe bends, flange interfaces, and pressure tubes under static overpressure, confirming zero leakage and absolute structural compliance.

After successful hydrostatic validation, the primary system undergoes hot conditioning. Heavy water is circulated through the circuit at elevated temperatures and pressures using main coolant pumps under precisely managed chemical conditions. Hot conditioning fosters the growth of a thin, highly adherent magnetite passivating film on internal carbon steel piping surfaces. This protective layer prevents ongoing aqueous corrosion, minimizes metal release into the coolant, and reduces radiation field buildup throughout future operating cycles.

Strategic Value for India’s Clean Energy Blueprint

The successful core overhaul and upcoming restart of Kaiga Unit-1 carry major strategic value for India’s clean energy goals. Alongside NPCIL’s ongoing rollout of new 700 MWe PHWRs, extending the operating life of existing 220 MWe reactors provides a cost-effective method to maintain reliable, zero-carbon base-load power. Extending the lifespan of mature nuclear units by 25 to 30 years maximizes return on existing capital investments while supporting grid stability in key industrial corridors.

Additionally, the engineering methodologies and specialized tooling validated at KGS-1 establish a proven framework for upcoming refurbishment cycles across India’s operating PHWR fleet. Integrating automated non-destructive evaluation systems, high-precision hydraulic tooling, remote welding units, and specialized fluid conditioning skids ensures that future reactor overhauls can be performed with enhanced safety, reduced technician dosage, and minimal plant downtime.

Indigenized Test Infrastructure and High-Pressure Engineering

As India expands its nuclear capacity and executes critical life-extension overhauls across its energy infrastructure, the requirement for dependable ground testing equipment and specialized fluid systems becomes paramount. Overhauling pressurized heavy-water loops demands precise validation, where high-pressure leak testing skids, hydrostatic test rigs, snubber testing systems, and automated fluid benches must operate with absolute reliability. At Neometrix Defence Limited, we engineer custom high-pressure gas test benches, hydraulic test rigs, snubber test systems, and turnkey fluid qualification infrastructure that empower Indian power utilities and industrial leaders to uphold world-class quality, safety, and domestic self-reliance.