Light Water Reactors (LWRs): India’s Strategic Shift in Nuclear Energy

Learn about Light Water Reactors (LWRs), their types, differences from PHWRs, why India is developing an indigenous 900 MWe LWR, and how the dual-track nuclear strategy strengthens energy security and clean energy goals.

Table of Contents

Context

The Department of Atomic Energy (DAE) is prioritising the expedited development of a 900 MWe indigenous LWR, with design work initiated in 2015.

About Light Water Reactors

The light-water reactor (LWR) is a type of thermal-neutron reactor that uses normal water, as opposed to heavy water, as both its coolant and neutron moderator.
There are three varieties of light-water reactors: the pressurized water reactor (PWR), the boiling water reactor (BWR), and (most designs of) the supercritical water reactor (SCWR).

Difference Between LWRs and PHWRs

Aspect	LWRs	PHWRs
Moderator	Light water (H₂O)	Heavy water (D₂O)
Coolant	Light water	Heavy water
Fuel	Enriched uranium	Natural uranium
Enrichment Requirement	Required	Not required
Global Presence	Dominant worldwide	Limited outside a few countries
Construction Cost	Generally lower due to scale	Higher due to heavy water use
Fuel Flexibility	Limited	High (thorium, LEU blends possible)

Why is India pushing for LWRs

- Global Dominance: LWRs account for over 85% of global civil nuclear reactor capacity, making them the standard technology in international markets.

Design and Cost Advantages:

- Use normal (light) water as both coolant and moderator.
- Simpler engineering overlaps with conventional thermal power technologies.
- Benefit from economies of scale, resulting in lower construction costs and higher thermal efficiency.
Export Imperative: An Indian LWR would strengthen India’s bargaining power with foreign vendors and support export ambitions.

Concerns with LWRs

Cost and Tariffs: Imported LWR projects involve higher capital costs, potentially leading to higher electricity tariffs in the Indian context.
Indigenous Capability Risk: Excessive reliance on imports could undermine domestic PHWR manufacturing capacity.
Fuel Access: LWRs require enriched uranium, which is readily available internationally but historically constrained for India.

Significance of India’s Dual-Track Approach

Integrated Strategic Vision: As India opens its nuclear power sector to private participation and explores reactor exports and small modular reactors (SMRs), it is pursuing a dual-track nuclear strategy that combines LWRs and PHWRs.
Strengthening India’s Credibility: A diversified reactor portfolio enhances India’s standing as a credible and reliable nuclear supplier, particularly for emerging economies in the Global South seeking affordable and scalable clean energy solutions.
Advancing Clean Energy Transition and Energy Security: The dual-track approach supports India’s clean energy transition by expanding low-carbon power generation while reducing dependence on fossil fuels and improving long-term energy security.
Energy diplomacy: Nuclear capabilities increasingly function as a tool of energy diplomacy, complementing India’s outreach through infrastructure development and digital public goods to strengthen strategic partnerships.

Heavy Water

Heavy water (D₂O) is water in which hydrogen atoms are replaced by deuterium, an isotope of hydrogen containing one proton and one neutron.
It is an excellent neutron moderator, slowing down neutrons without absorbing them significantly, making it ideal for use in Pressurised Heavy Water Reactors (PHWRs).
Heavy water enables the use of natural uranium as nuclear fuel, eliminating the need for uranium enrichment.
It can also produce plutonium suitable for nuclear weapons if misused.
Owing to this dual-use nature, heavy water is classified as a strategic nuclear material under international non-proliferation regimes.
Its production, transfer, and export are monitored under frameworks such as the International Atomic Energy Agency (IAEA) safeguards system.