‘Spillage to open reactor’ phase kicks off at Kudankulam nuclear plant’s unit 3

Kudankulam Nuclear Power Plant (KKNPP) Unit 3 has commenced the "spillage to open reactor" phase — a critical pre-commissioning activity. The phase involves ...

What Happened

Kudankulam Nuclear Power Plant (KKNPP) Unit 3 has commenced the "spillage to open reactor" phase — a critical pre-commissioning activity.
The phase involves flushing of safety systems and main coolant pipelines (MCP) using light water to ensure cleanliness and conformance with design specifications before nuclear fuel is loaded.
According to NPCIL, this milestone marks "the start of individual functional testing of primary system equipment and piping in accordance with design requirements" — a critical step toward commissioning the plant.
The commencement was inaugurated by the Chairman and Managing Director of NPCIL, in the presence of senior officials from Atomstroyexport (ASE), the Russian agency overseeing construction.
Unit 3 is expected to be commissioned in 2026; Unit 4 is at an advanced stage of construction, while Units 5 and 6 are at various earlier construction stages.

Static Topic Bridges

Kudankulam Nuclear Power Project (KKNPP)

Kudankulam Nuclear Power Project is located in Tirunelveli district, Tamil Nadu, and is being developed under an Inter-Governmental Agreement between India and Russia. Units 1 and 2 (each 1,000 MW VVER-type pressurised water reactors) are fully operational, contributing 2,000 MW to the southern grid. Units 3 and 4 (each 1,000 MW) are being constructed under a follow-on agreement. Units 5 and 6 are at earlier stages of construction, together adding another 2,000 MW. When all six units are operational, KKNPP will have a total capacity of 6,000 MW — making it the largest nuclear power station in India.

Location: Tirunelveli district, Tamil Nadu
Technology: VVER-1000 (Water-cooled Water-moderated Energy Reactor) — Russian pressurised water reactor design
Units 1 & 2: Operational (2,000 MW combined)
Units 3 & 4: Under construction (2,000 MW combined); Unit 3 expected commissioning 2026
Units 5 & 6: Under construction (2,000 MW combined)
Total planned capacity: 6,000 MW (upon completion of all 6 units)

Connection to this news: The spillage to open reactor milestone in Unit 3 is the immediate precursor to hot testing and fuel loading — the last stages before Unit 3 begins generating electricity.

Nuclear Power Corporation of India Limited (NPCIL) and Atomic Energy Act

NPCIL is a Government of India enterprise under the Department of Atomic Energy, responsible for design, construction, commissioning, and operation of nuclear power plants in India. It operates under the Atomic Energy Act, 1962, which established the Atomic Energy Commission and conferred on the central government monopoly over atomic energy production. In December 2025, Parliament passed the Sustainable Harnessing and Advancement of Nuclear Energy for Transforming India (SHANTI) Bill, which replaced the 1962 Act and for the first time allows private companies and joint ventures to participate in the nuclear energy sector.

NPCIL established: 1987 (under the Companies Act), under Department of Atomic Energy
Governing law: Atomic Energy Act, 1962 (replaced by SHANTI Act, December 2025)
SHANTI Act: allows private companies to own, build, and operate nuclear power plants — a historic policy shift
Regulatory oversight: Atomic Energy Regulatory Board (AERB)
As of early 2025: India has 25 reactors operational with installed capacity of 8,880 MW

Connection to this news: KKNPP Unit 3's commissioning will take place under the new SHANTI Act framework, which also opens the door to private sector nuclear investment — making the timing of this milestone doubly significant for energy policy.

India's Three-Stage Nuclear Power Programme

India's three-stage nuclear power programme was conceptualised by Dr. Homi Jehangir Bhabha to address India's limited uranium reserves but vast thorium reserves (approximately 25% of global thorium). The programme, adopted by the government in 1958, envisions a long-term pathway to thorium utilisation: - Stage 1: Natural uranium-fuelled Pressurised Heavy Water Reactors (PHWRs) generate electricity and produce plutonium-239 as a by-product. - Stage 2: Plutonium-239-fuelled Fast Breeder Reactors (FBRs) generate electricity and breed more fissile material (including U-233 from thorium blankets) than they consume. - Stage 3: U-233-fuelled Advanced Heavy Water Reactors (AHWRs) run on thorium, achieving India's long-term energy security.

Architect: Dr. Homi Jehangir Bhabha (formally adopted 1958)
Stage 1 (current): PHWRs + LWRs (including KKNPP's VVER reactors imported from Russia)
Stage 2 (in progress): Prototype Fast Breeder Reactor (PFBR) at Kalpakkam — under commissioning
Stage 3 (future): AHWRs utilising India's thorium reserves
India's thorium reserves: ~25% of global reserves

Connection to this news: KKNPP's water-cooled reactors are Stage 1 technology. Their expansion directly increases the plutonium stockpile that fuels Stage 2, moving India closer to energy self-sufficiency under the three-stage programme.

India-Russia Nuclear Cooperation

India-Russia civil nuclear cooperation dates to 1988 when the two countries signed an agreement for KKNPP. Russia's state nuclear corporation Rosatom — through its subsidiary Atomstroyexport (ASE) — is the engineering, procurement, and construction (EPC) contractor for all six KKNPP units. Russia also supplies the initial nuclear fuel (LEU). The partnership is governed by an Inter-Governmental Agreement and supplemented by project-specific protocols. KKNPP is one of the flagship projects of the Indo-Russian strategic partnership.

Partnership: India (NPCIL) + Russia (Rosatom/ASE)
Agreement origin: 1988 Inter-Governmental Agreement
Russia's role: technology provider, EPC contractor, initial fuel supplier
Units 1–4 under original agreement; Units 5–6 under a follow-on agreement (2017)

Connection to this news: The presence of ASE's Director for Indian Projects at the Unit 3 commissioning milestone reflects the active and ongoing nature of this bilateral nuclear cooperation.

Key Facts & Data

Kudankulam Nuclear Power Plant, Tirunelveli district, Tamil Nadu — India-Russia joint project
Current milestone: "Spillage to open reactor" phase for Unit 3 — flushing of safety systems and main coolant pipelines
Units 1 & 2: Operational (2,000 MW); Unit 3 target commissioning: 2026; Unit 4: advanced construction; Units 5 & 6: earlier construction stages
Total planned capacity: 6,000 MW — will be India's largest nuclear power station
Reactor type: VVER-1000 (Russian pressurised water reactor)
Operator: NPCIL (Nuclear Power Corporation of India Ltd)
Construction partner: Atomstroyexport (ASE), a subsidiary of Rosatom (Russia)
India's current nuclear installed capacity (early 2025): 8,880 MW from 25 reactors
New legislative framework: SHANTI Act (December 2025) replaced Atomic Energy Act 1962, opened nuclear sector to private participation