Gaurav Arya | Energy Decoded Newsletter | April 2026
At 8:25 PM on April 6, 2026, a chain reaction started inside a reactor at Kalpakkam, Tamil Nadu, and did not stop. That is what nuclear scientists call “first criticality.” It means the reactor is self-sustaining.
The Prototype Fast Breeder Reactor (PFBR) had been under construction since 2004. It was supposed to be commissioned by 2010. It missed that deadline, then several more. But on Monday evening, the Atomic Energy Regulatory Board gave clearance, and BHAVINI switched it on. With that, India officially entered Stage 2 of a three-stage nuclear programme conceived by Dr. Homi Jehangir Bhabha in the 1950s.
Section 1: The Plan Bhabha Drew Up in the 1950s
India has very little uranium — estimated domestic reserves of around 70,000 tonnes. However, India holds the world’s third-largest reserves of thorium (~360,000 tonnes). If those reserves could be converted into usable nuclear fuel, India would have an almost inexhaustible energy supply. The problem is that thorium cannot power a reactor directly. It needs to be transmuted into Uranium-233 first. That conversion requires fast neutrons, which conventional reactors do not produce in adequate quantities. Fast Breeder Reactors do.
Bhabha’s solution was a three-stage programme:
- Stage 1: Use natural uranium in Pressurised Heavy Water Reactors (PHWRs) to generate electricity and plutonium as a by-product.
- Stage 2: Use that plutonium to fuel Fast Breeder Reactors, which produce more fuel than they consume while converting thorium into Uranium-233.
- Stage 3: Use that Uranium-233 to run thorium-based reactors at scale.
India has been in Stage 1 since 1969. It took 57 years to get to Stage 2. India’s thorium reserves could, theoretically, generate 500 GW of electricity for several hundred years.
Section 2: What the PFBR Actually Does
The PFBR at Kalpakkam is a 500 MWe reactor — enough to power a mid-sized city. It was designed and built entirely indigenously by IGCAR and BHAVINI. Unlike a conventional reactor, a fast breeder uses high-energy “fast” neutrons. The core burns a mixture of Uranium-238 and Plutonium-239. Around the core is a “blanket” of Uranium-238 — fast neutrons convert this into new Plutonium-239, producing more fissile material than the reactor consumes. It also uses liquid sodium as its coolant, which is highly efficient but considerably more complex to manage.
Achieving first criticality does not mean the PFBR is generating electricity yet. Commercial operation is likely in late 2026 or early 2027. When it does reach full power, India will become only the second country in the world — after Russia — to operate a commercial fast breeder reactor.
Section 3: The Policy Architecture Around It
The Nuclear Energy Mission (Budget 2025-26) committed Rs 20,000 crore to Small Modular Reactors. The target is at least five indigenously designed and operational SMRs by 2033.
The SHANTI Act (December 2025) is the structural reform that deserved more coverage. The Act repealed the Atomic Energy Act of 1962 — a 63-year-old law that prevented private sector participation entirely. Under the new law, private companies can build, own, operate, and decommission nuclear power plants. Foreign direct investment is permitted up to 49%. The Act also fixed a liability problem that had frozen the US-India civil nuclear relationship for 15 years, replacing unlimited supplier liability with a graded, capped structure — effectively removing the single biggest barrier to Indo-US nuclear trade.
Companies that have signalled interest include Tata Power, Naveen Jindal Group, and Vedanta. Holtec International called the SHANTI Act “transformative.”
Section 4: The Numbers
- Current installed nuclear capacity: 8,780 MW (24 reactors)
- Reactors under construction: 8 reactors, 6,600 MW
- Projected capacity by 2031-32: 22,380 MW (nearly 3× current)
- Target capacity by 2047: 100,000 MW (100 GW)
- Nuclear Energy Mission SMR budget: Rs 20,000 crore
- Current share of nuclear in India’s power mix: Under 2%
The 100 GW target by 2047 requires a 12-fold increase from today. Public sector entities (NPCIL, BHAVINI) are expected to account for 58-60 GW. The remaining 40-42 GW is expected from private and joint-venture capacity enabled by the SHANTI Act.
Section 5: The Honest Constraints
The PFBR was originally due for commissioning in 2010. It took 16 additional years. This is not unusual for first-of-kind reactor technology — but it is worth holding alongside the enthusiasm.
The uranium supply chain remains a structural risk. India imports from Kazakhstan and Russia to supplement its modest domestic reserves. The SHANTI Act’s 49% FDI cap and retention of DAE control over fuel-cycle activities will limit how quickly foreign companies can fully commit capital. And the 100 GW by 2047 target is ambitious — nuclear has none of solar’s structural advantages of modularity and rapid cost reduction.
What We Think
India’s nuclear strategy is architecturally sound. Bhabha’s three-stage logic was designed for exactly the resources India has, and the PFBR is the first real step beyond the theoretical. The SHANTI Act was long overdue. The SMR programme, if it executes on time, could be genuinely transformative for industrial baseload power and green hydrogen.
What India has not solved is the pace problem. Watch three signals in the next 18 months: Will the PFBR reach commercial operation by late 2026? Will any private company sign a binding commitment under the SHANTI Act? Will BSMR-200 receive administrative approval and break ground at Tarapur? These are a more honest measure of India’s nuclear future than any government document.
Sources: Department of Atomic Energy press release (April 7, 2026); PIB Factsheet; Lok Sabha written reply by Minister Jitendra Singh (March 11, 2026); SHANTI Act 2025 official document; Physics World (January 2026); World Nuclear News.