#xix Beyond Citations | India’s nuclear renaissance, one pressurised heavy reactor at a time
What are PHWRs and why are they central to India’s nuclear dream?
In the #v edition of Beyond Citations, I closely examined the question of nuclear liability in light of Sitharaman’s budget announcement on nuclear energy.
In her budget speech on 1 February 2025, India’s finance minister Sitharaman announced that the government plans to amend both the CLNDA and Atomic Energy Act to foster private sector involvement in India’s civil nuclear energy sector with the ultimate goal of achieving 100 GW nuclear power by 2047.
While budget speeches have been important markers of policy priorities of successive Indian governments, some announcements not anchored in matter-of-fact budgeted numbers are not necessarily realised in the same financial year.
But with the nuclear energy announcement, it seems that the government means business after all. On June 30, Anil Sasi for the Indian Express reported:
Legislative groundwork is underway for multiple amendments to two overarching laws governing the country’s atomic energy sector. The changes will align them with legal provisions globally, address festering investor concerns and set the stage for opening up India’s civil nuclear sector.
He added that around 11 amendments are being worked out for the liability law alone, focusing on the section 17(b), alignment with global convention on nuclear liability and clarifying who constitutes a supplier. But when would these amendments be introduced? Citing an official source, Sasi reports that ‘the amendments are now likely to spill over beyond the monsoon session.’
As much as overhauling the liability law and opening the nuclear sector for more private sector participation are beneficial, they are not the only silver bullet India needs. One aspect that is often overlooked in discussions around increasing nuclear generation capacity in the country is the success of the first stage of India’s nuclear power programme involving the pressurised heavy water reactors (PHWRs).
As I argued in my recent Moneycontrol piece, India needs to urgently double ‘down on PHWRs, a technology that India has successfully indigenised.’
The country can build these PHWRs either in the small modular reactor style (300 MW or less) or as large reactors (700 MW or more). The NSG waiver means that India can strike bilateral deals with uranium-rich countries to secure natural uranium to run these reactors which would be under International Atomic Energy Agency safeguards. While other reactor types from the West are welcome, India should not overlook its own successful reactor design in pursuance of external ones.
But what are these PHWRs that form the core of India’s nuclear dream — past, present and future?
If there is one book that explains everything about India’s nuclear energy journey (from technical to historical), it is the following little-known brief book by Saurav Jha:
Saurav Jha, The Upside Down Book of Nuclear Power (HarperCollins, 2010). https://www.sauravjha.com/books/the-upside-down-book-of-nuclear-power/
The most significant word in a PHWR is ‘heavy’ and it has to do with water. What we normally call water is composed of two atoms of hydrogen combined with one atom of oxygen. The catch here is that the hydrogen only has one proton in its nucleus. What we call heavy water, on the other hand, has the same hydrogen-oxygen composition but Hydrogen’s nucleus also has a neutron in addition to a proton. Hence light water is H20 (hydrogen oxide) while heavy water is D20 (deuterium oxide).
In PHWRs, heavy water is used both as a moderator and a coolant. Why?
Because heavy water is a good moderator, and it slows down the fast moving neutrons that have just been released as the uranium fuel fissions. But being a good moderator, it does not absorb too many neutrons even as it slows them down. It is the usage of heavy water as moderator that makes it possible to sustain a chain reaction in natural uranium (about 0.7 per cent of fissionable U-235 and 99.3 per cent fertile U-238). It is also the heavy water that makes it possible to breed plutonium (Pu-239) within a PHWR.
Because PHWRs avoided the need to enrich uranium and could also be used to produce plutonium, the founders of the Indian nuclear establishment envisioned this reactor type as the mainstay of the first stage of India’s nuclear programme.