Knowledge Nugget: India flags the Indigenous Light Water Reactor (LWR) as nuclear priority. But why?

This is also the backdrop to the Sustainable Harnessing and Advancement of Nuclear Energy for Transforming India (SHANTI) Act, 2025, passed in the winter session of Parliament, which opens up the possibility of more imported LWR-based nuclear projects of the kind being set up by the Russians in Kudankulam.

In today’s Knowledge Nugget, let’s not only know about the LWR but also India’s three-stage nuclear programme. 

Key Takeaways:

1. Light Water Reactors form a mainstay of the global nuclear program; these use light water, enriched uranium, and have simpler design, lower construction cost, economies of scale, and high thermal efficiency.

2. LWRs currently account for over 85% of the civil nuclear reactor capacity in the world. There are at least three reasons for this trend:

(i) LWRs entail simpler design and engineering compared to heavy water reactors given that they use normal water as both coolant and moderator and so have some degree of overlap with the technology used by regular thermal power units (coal-fired and gas-based power plants); 

(ii) They typically entail lower construction cost on account of economies of scale, given that LWRs make up most of the installed nuclear capacity; these reactors are seen as being more thermal efficient.

(iii) While LWRs use normal water, they need enriched uranium as fuel. Given that access to enriched uranium is not a constraint in much of the western world, LWRs are used extensively by the US, Russia and France and now form the backbone of most international reactor fleets.

Why does the light water reactor matter?

1. Having an indigenous LWR, alongside the exis­­ting fleet of pressurised heavy water reactors (PHWR), is expected to boost India’s leverage in dealing with foreign vendors to secure better terms in imports, officials said.

2. Significantly, LWRs constitute the bulk of the international reactor market, and without integrating Indian companies into the global supply chain, making a breakthrough in the export segment is likely to be difficult.

3. The legal changes brought by SHANTI Act are seen within the establishment as necessary to tap the dominant global LWR ecosystem, even as India retains its core strengths in other reactor types.

4. Notably, India’s civil nuclear programme has deep expertise in manufacturing heavy water reactors from 220 MWe PHWRs to the new 700 MWe units. Based on heavy water (deuterium) and natural uranium, PHWRs are a technology that India’s nuclear establishment has mastered. However, these are increasingly out of sync with LWRs, which now dominate the global market.

India’s Three-stage nuclear programme

1. India’s nuclear journey began shortly after Independence with the establishment of the Atomic Energy Commission in 1948. In 1956, Asia’s first research reactor, Apsara, was commissioned at the Bhabha Atomic Research Centre (BARC) in Trombay.

2. India was the second Asian nation to build a nuclear power plant in 1969 at Tarapur, just after Japan and long before China. It also built up an impressive nuclear research and development programme in the 1950s and 1960s with significant assistance from its Western partners.

3. India owes the vision of the three-phase programme of nuclear power to ensure energy security to Dr Homi J Bhabha, the father of India’s nuclear programme, and Dr Vikram Sarabhai, who recognised the need for developing fast breeder reactors (FBRs), as these reactors generate more nuclear fuel than they consume due to the gainful conversion of fertile isotopes into fissile material.

→ STAGE 1: Pressurised Heavy Water Reactors (PHWRs) use natural uranium-based fuels to generate electricity, while producing fissile plutonium (Pu239), which can be extracted by reprocessing the spent fuel. It uses heavy water (deuterium oxide) both as a coolant and moderator. The programme has been supplemented by the construction of imported Light Water Reactors (LWRs).

→ STAGE 2: It involves setting up Fast Breeder Reactors (FBRs) of the kind at Kalpakkam, using plutonium-based fuels, which can enhance nuclear power capacity, and convert fertile thorium into fissile uranium (U233). Reprocessing of the spent fuel is vital for efficient utilisation of the plutonium inventory.

→ STAGE 3: The third stage will be based on the ThU233 cycle. U233 produced in the second stage can be used for the third stage of the power programme, which consists of advanced thermal and fast breeder reactors, for long-term energy security. The Advanced Heavy Water Reactor (AHWR) is proposed for this. Now, the use of molten salt reactors is also seen as an option.

BEYOND THE NUGGET: What is SHANTI ACT, 2025?

1. Earlier in December, Parliament had passed the Sustainable Harnessing and Advancement of Nuclear Energy for Transforming India (SHANTI) Act, 2025, which marked a major shift in how India’s tightly-controlled nuclear power sector will be governed in the coming years.

2. This Act is an effort to align with norms of global nuclear commerce. It replaces the Atomic Energy Act of 1962 and the Civil Liability for Nuclear Damage Act of 2010 with a single umbrella law.

3. The new law allows public and private companies to set up nuclear power plants and undertake activities related to the transport, storage, import and export of nuclear fuel, technology, equipment and minerals. Until now, these activities were restricted to public sector entities only.

Post Read Question

Consider the following statements with respect to Light Water Reactors:

1. They form a mainstay of the global nuclear program.

2. They use light water, enriched uranium, and have a simpler design. 

3. They currently account for over 85% of the civil nuclear reactor capacity in the world.

How many of the statements given above are correct?

(a) One only

(b) Two only

(c) All three

(d) None

(Sources: DAE’s nuclear pivot: Light water push to tap global markets, retain heavy water edge,SHANTI Bill: How India is overhauling its nuclear power sector, Knowledge Nugget: India’s three-stage nuclear programme)

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