In an essential milestone, the prototype fast breeder reactor (PFBR) at Kalpakkam achieved criticality on April 6. The time period ‘criticality’ is acquainted to India: over the a long time, it has been related to the sluggish and tedious successes of India’s nuclear energy programme. At the identical time, in step with many phrases within the nuclear vocabulary, ‘criticality’ can be typically mistaken as an finish aim. In actuality, it’s really step one.
What is criticality?
A nuclear reactor turns into essential when its chain reaction is ready to maintain itself. That is, when an atom’s nucleus undergoes nuclear fission, it releases neutrons that set off at the very least another fission response within the surrounding nuclei. Reactor engineers guarantee this occurs by controlling the composition of the gas (the fabric whose nuclei bear fission), how effectively the neutrons are in a position to ‘access’ extra nuclei, and the temperature of the reactor.
Once a reactor is essential, it additionally means it’s in a sort of steady state. However, it does not imply that it’s working in a commercially viable method. That comes a lot later. After criticality, the operators hold the reactor working because it produces a low quantity of energy, for months if obligatory, whereas they examine if its working parameters are inside design limits. If an operator is bound that the parameters are, they will go to the subsequent stage.
How do FBRs work?
Most of India’s presently working nuclear reactors are pressurised heavy water reactors (PHWRs). They are designed to help the fission of pure uranium. Natural uranium consists of 99.3% of uranium-238 and 0.7% of uranium-235. ‘235’ and ‘238’ denote the full variety of protons and neutrons within the nucleus. In a PHWR, neutrons are launched into the reactor, the place a tool known as a moderator slows them down. This is critical for the neutrons to trigger uranium-235 to bear fission. When it does, it releases warmth, which the PHWR converts to electrical energy; a small quantity of plutonium; and some neutrons.
PHWRs are inefficient as a result of solely a small fraction of the gas, round 1%, undergoes fission earlier than it turns into unusable.
A fast-breeder reactor (FBR) is extra environment friendly, attaining a gas use price of round 10% or extra. Mainly, the gas consists of plutonium, not uranium. The reactor core is surrounded by a ‘blanket’ of depleted uranium, just like the unusable gas produced by PHWRs. When a fast neutron bombards the blanket, the uranium nuclei are transmutated to plutonium nuclei, that are reprocessed as nuclear gas. The plutonium-based gas additionally makes use of the fast neutrons to bear fission, releasing extra fast neutrons.
What is India’s three-stage programme?
The nuclear physicist Homi Bhabha is extensively credited with conceiving India’s nuclear programme within the first years of its independence. The programme has three levels. In the primary stage, PHWRs will use pure uranium to provide plutonium and depleted uranium and electrical energy. In the second, FBRs will use the plutonium and depleted uranium from the primary stage to provide much more plutonium and electrical energy. Finally, future nuclear reactors will use plutonium and thorium to provide electrical energy.
Bhabha got here up with this programme as a result of India has considerable portions of thorium however solely modest reserves of uranium.
And on this scheme, FBRs have been envisaged as a bridge between the preliminary step, to make use of what now we have, and the ultimate step, to finish the cycle and thus make India self-sufficient in nuclear energy.
Why are FBRs difficult?
That an FBR is simpler mentioned than completed could be a gross underestimate. The Indian authorities permitted the PFBR greater than twenty years in the past. It was designed by the Indira Gandhi Centre for Atomic Research and constructed by the Bharatiya Nabhikiya Vidyut Nigam, Ltd. The latter proved to be more difficult than first anticipated.
Among different options, the PFBR makes use of liquid sodium as coolant. Sodium turns into liquid at the next temperature, and at increased temperature warmth switch is extra environment friendly. Liquid sodium additionally does not must be pressurised. However, it reacts violently with air and water, so the pumps, pipes, and tanks uncovered to liquid sodium must be completely sealed, with stringent leak detection protocols. Water-cooled reactors wouldn’t have such operational complexities, nor the extra value.
India can be not alone in confronting these challenges. Japan’s Monju Nuclear Power Plant suffered a sodium leak and hearth in 1995, resulting in lengthy shutdowns; the plant finally needed to be decommissioned. The Superphénix in France was as soon as the world’s largest breeder reactor however it was shut down as effectively, as a consequence of technical points and excessive working prices, which additionally fanned political opposition. Russia, nevertheless, has continued to take care of a small fleet of fast-breeder reactors.
In different phrases, operators have proven FBRs to be technically possible however they aren’t but economically possible; they’ve additionally not received broader public acceptance. Aside from the prices of creating them, in addition they demand rigorous oversight — which is dependent upon each engineering excellence and the protection tradition.
How has India pursued FBRs?
India is pursuing FBRs as a result of, as mentioned earlier, the three-stage nuclear programme prioritises long-term gas safety. Importantly, it’s ready to take action as a result of India’s nuclear sector stays largely pushed by the state. Its decision-making construction is comparatively insulated from the ruling institution: the Department of Atomic Energy (DAE) experiences on to the Prime Minister’s Office. As a consequence, so long as there was political stability, India has been in a position to maintain nuclear initiatives throughout electoral cycles.
On the flip aspect, this insulation has lowered scrutiny of the nuclear energy programme and guarded it from the identical stress to ship that assails different public sector enterprises just like the Indian Railways and the National Highways Authority. Engineers have taken on initiatives with restricted transparency on timelines and budgets. When one or each have slipped, the accountability has been unfold throughout businesses. The PFBR’s authentic value was Rs 3,500 crore. It got here to Rs 6,800 crore in 2019. The DAE additionally sought a number of deadline extensions. In 2020, it mentioned the PFBR could be commercialised in October 2022. That milestone continues to be pending.
The economics of FBRs additionally stay unsure. In addition to the aforementioned points, the broader gas cycle — particularly the reprocessing of spent gas and the fabrication of latest gas assemblies — would require its personal infrastructure. And for this the nuclear institution should arrange new regulatory processes.
What subsequent for the PFBR?
The PFBR shall be operated at a low energy degree to examine its behaviour in several working circumstances. Engineers will accumulate the info from these exams to tell selections about elevating the reactor’s energy output and refining security protocols. Eventually, they’ll search approval from the Atomic Energy Regulatory Board to function the reactor in business mode.
This entails working the PFBR at or close to its rated capability to generate electrical energy for the grid on a sustained foundation, with commonplace working procedures and clear regulatory oversight. At this cut-off date, the reactor may also have transitioned from being experimental to a business energy plant.
In parallel, the DAE may also develop gas reprocessing amenities and plan for future FBRs. Once these goals are nearer to being realised, the federal government and India will develop a clearer sense of whether or not the broader imaginative and prescient of a closed fuel-cycle may be realised.
mukunth.v@thehindu.co.in
Published – April 08, 2026 07:45 am IST
