Bharat Rakshak

FWIW - If anyone is interested, there is also a very counter-intuitive reactor-physics detail about thorium in thermal reactors—namely that U-233 actually has better neutron characteristics than Pu-239 in thermal spectra.

It is is one of the most interesting reactor-physics subtleties in the thorium debate, and it is rarely explained clearly.
Allow me to expand it here:

The counter-intuitive point: U-233 is an exceptionally good thermal fissile isotope:

In a thermal neutron spectrum, Uranium-233 actually has more favorable neutron characteristics than either Uranium-235 or Plutonium-239.

The key parameter is the η (eta) value: ( = neutrons produced per absorption in fissile fuel
(tells you how many neutrons remain after a neutron is absorbed and causes fission)

Typical thermal-spectrum values are roughly:


U-233 -> η (thermal) ~ ~2.3
U-235 > η (thermal) ~ ~2.05
Pu-239> η (thermal) ~ ~2.1

So U-233 produces the most surplus neutrons per absorption.

(this matters for the thorium cycle)

Because U-233 has a higher η, a thermal-spectrum reactor can potentially breed while still producing power.

This is why thorium cycles are often paired with thermal reactors, unlike the U-238 → Pu-239 cycle, which generally needs fast breeders for breeding ratios >1.

The good η value does not automatically mean thorium reactors are easy to implement, because several practical issues appear:

(Protactinium-233 losses, U-232 contamination, Reprocessing complexity etc..

Efficient thorium breeding generally requires continuous or advanced reprocessing.
So while the neutron physics is attractive, the fuel-cycle engineering is difficult.

In the program designed by Bhabha

The logic was:
- Build fissile inventory (Pu-239) using PHWRs
-Expand fissile inventory with fast breeders
-Use that inventory to start thorium reactors producing U-233

The final stage benefits from U-233’s excellent thermal neutron performance, which allows efficient thorium utilization once the fissile base exists.

So in short:

Thorium cycles are attractive not because thorium itself is special, but because the fissile isotope it produces—U-233—has unusually favorable neutron physics in thermal reactors.

(There is one really elegant reactor-physics insight Bhabha emphasized that almost never appears in modern popular discussions but we physicists learn)

The thorium cycle potentially extracts more energy per tonne of mined material than the uranium-plutonium cycle.

It’s a beautiful piece of nuclear-fuel-cycle reasoning.

Also in the news:
Visakhapatnam chosen for high-energy proton accelerator
Facility to power India’s long-term thorium-based nuclear programme


This project is not just a physics accelerator—it is part of India’s long-term exploration of accelerator-driven thorium systems and advanced nuclear technologies.

The article describes is essentially India’s path toward an Accelerator-Driven System (ADS).

-A GeV-scale proton accelerator produces spallation neutrons.
-Those neutrons drive a subcritical reactor core.
-The core can potentially breed fissile material from thorium or burn long-lived actinides.

India has discussed this concept for many years as a possible thorium pathway complementary to fast breeders.
---

As a physicist, one detail about the Visakhapatnam proposal is particularly striking - the accelerator power implied in the article is extremely ambitious by global standards.

Particularly - I think, there is an interesting philosophical and technical difference between the Indian ADS concept and the European ADS programs.

While other ADS systems are mainly for waste transmutation. This (India) ADS seems mainly for thorium utilization and fissile production.

India’s primary path remains:
(PHWRs → produce Pu-239
-Fast breeder reactors → expand fissile inventory
-Thorium reactors → use U-233

ADS is viewed as a long-term complementary option, not a replacement.

But it could help with start (test) thorium systems earlier.
Test and/or reduce reactivity control challenges in thorium cores. It is extremely ambitious by global standards.

India developing 3 types of small modular reactors, govt tells LS

https://economictimes.indiatimes.com/ne ... aign=cppst

India is developing three different types of small modular reactors (SMRs), including one meant for hydrogen generation, the government informed the Lok Sabha on Wednesday.

In a written reply, Union minister Jitendra Singh stated that the three types are the 220 MWe Bharat Small Modular Reactor (BSMR-200), the 55 MWe SMR (SMR-55), and a 5 MWth high-temperature gas-cooled reactor (HTGCR) for hydrogen generation.

"Lead units of these SMRs will be constructed by DAE (Department of Atomic Energy) at its existing sites. Tarapur Atomic Power Station site, Maharashtra, has been identified for lead units of BSMR-200 and SMR-55, whereas the Vizag, Andhra Pradesh site of BARC is identified for high temperature gas-cooled reactor," Singh said.

While the development and construction of BSMR-200 will cost Rs 5,960 crore, SMR-55 (two units) and HTGCR will cost Rs 7,000 crore and Rs 320 crore.

"Estimated time for construction of BSMR is 60 to 72 months from receipt of administrative and financial approval," Singh added.

Currently, eight nuclear power reactors with a total capacity of 6600 MW are at various stages of construction/commissioning, and 10 reactors (7000 MW) are under pre-project activities. PTI

^^^ Thanks. Also in the Mint:

India's nuclear energy mission: ₹20,000 crore provision, BARC to deploy rectors, 100 GW capacity goal — Latest updates

Both articles describe the same program, but they emphasize different aspects of India’s SMR initiative. One focuses on funding and mission structure, while the other reports the government’s formal statement to Parliament.

Both describe India is developing three SMR designs:
-BSMR-200 – 220 MWe Bharat SMR
-SMR-55 – 55 MWe small reactor
-HTGCR – ~5 MWth high-temperature gas-cooled reactor for hydrogen generationMint article

Mint article focuses on policy and financing: (₹20,000-crore government mission,connection to 100 GW nuclear roadmap.

Some iImportant technical implications (not emphasized in either article)
- India is using PHWR heritage for SMRs (Unlike Western SMRs (PWR/BWR))
- India’s BSMR-200 derives from PHWR technology. (Using heavy-water moderation. on power refuling)
This is unique among SMR programs globally.

- The 55 MW reactor is unusually small

Globally most SMRs are 250–470 MW.
India’s 55 MW unit is closer to a micro-grid or industrial reactor.

Possible uses - ( As said, captive industrial power, replacement of coal units, desalination etc..)

- ) The hydrogen reactor is experimental

The 5 MWth HTGR is clearly not for grid electricity.

Purpose: high-temperature heat, hydrogen production, technology demonstration).

It is comparable to research reactors in other SMR programs.

- Strategic context both articles imply

Goal it to from ~8–9 GW nuclear capacity to 100 GW by 2047

SMRs are only a small part of that expansion. Subtle misconception in the media narrative

Both articles implicitly suggest SMRs are central to the 100 GW plan.
That is unlikely.

In practice:

SMRs will likely serve industrial and distributed energy roles,

while large reactors provide the bulk capacity.
---
Short:

Both articles describe the same SMR program.
The Mint article explains the funding and strategic mission.
The Economic Times article confirms the reactor designs and deployment plan through Parliament.
Together they show that India is building a three-tier SMR program:

BSMR-200 → main small power reactor
SMR-55 → micro-grid / captive reactor
HTGR-5 → hydrogen/process heat reactor.

*****
Some comments/Questions:

The articles describe the SMR program but omit a critical technical question:

What fuel will BSMR-200 use?
-If natural uranium, it remains fully aligned with India’s traditional PHWR model.
-If slightly enriched uranium, it improves SMR economics but changes the fuel-cycle and safeguards dynamics.
For nuclear engineers, that single detail strongly influences reactor physics, economics, and geopolitics.

I dont think we should have LPG for home and work towards moving to all electric coupled with aggressive home based solar over next decade. IMO that is more sustainable, even cheaper, and furthers energy security!

LPG subsidy could be added to home solar subsidy if used for cooking!

Kakkaji wrote: ↑12 Mar 2026 06:07 India developing 3 types of small modular reactors, govt tells LS

https://economictimes.indiatimes.com/ne ... aign=cppst

GoI press release on the same:
https://www.pib.gov.in/PressReleasePage ... g=3&lang=1

begins:

Under the Nuclear Energy Mission announced in the Union Budget 2025–26, a total budgetary provision of ₹20,000 crore has been made for the research, design, development, and deployment of Small Modular Reactors (SMRs). Department of Atomic Energy (DAE) has undertaken design and development works on indigenous SMRs namely;

220 MWe Bharat Small Modular Reactor (BSMR-200)
55 MWe Small Modular Reactor (SMR-55), and
Up to 5 MWth High temperature gas cooled reactor meant for hydrogen generation.
The lead units of these SMRs will be established at DAE sites for technology demonstration.

The progress of these SMRs is as follows;

BSMR-200: In-principle approval has been received for the project. Proposal for administrative & financial sanction is cleared by Atomic Energy Commission (AEC) for submission of the proposal to the Cabinet Committee.
SMR-55: In-principle approval has been received for the project.
HTGCR: In-principle approval has been received for the project. Detailed Project Report (DPR) has been prepared. Siting consent has been received and Terms of Reference (ToR) for obtaining environmental clearances has been received from Ministry of Environment, Forest and Climate Change (MoEF&CC).

Another article in NDTV: "Abandoning Thorium As Energy Source Is Suicidal For India," Scientist Warns


Here’s a brief summary of the NDTV article, followed by a technical/strategic commentary, my comments:

This piece reports a warning from an Indian nuclear scientist that:
->India should fully pursue the thorium fuel cycle rather than neglect it.
->Thorium offers a path to long-term energy independence, especially given India’s large thorium reserves.
->Relying on imported fuels (oil, gas, even uranium) exposes India to geopolitical risks and supply disruptions.
->Developing thorium-based nuclear power would help insulate India from global energy shocks and reduce dependence on imports.

In essence
-> Not pursuing thorium = strategic vulnerability for India.

My take (as usual): The statement is directionally correct, but overstated in tone. Let’s unpack it carefully.

1. The core claim is fundamentally valid
From a resource physics + energy security perspective, thorium is indeed attractive.

2. But “abandoning thorium is suicidal” is an exaggeration

The bottleneck is not political will—it is physics + engineering maturity.
These are not yet commercially proven at scale anywhere in the world.

So India is not “abandoning” thorium—it is: -> sequencing it cautiously through the three-stage program

3. India is already pursuing thorium—just indirectly
So the real situation is: Thorium is central, not abandoned but it is stage 3, not immediate deployment.

4. The real constraint: fissile inventory, not thorium
(This is the key technical point often missed in media)

Thorium is abundant—but fissile material is not
So the limiting factor is: initial fissile inventory, not thorium availability. This is why fast breeders are critical.

5. Time-scale mismatch (this is the real issue)

Thorium is a long-term (2050–2070) solution, not a near-term one.

India’s urgent needs are: decarbonization, grid-scale capacity, energy security now
These are better served by: PHWR-700 fleet, imported LWRs, possibly SMRs
Thorium cannot yet deliver at that scale in the next 10–20 years.

6. Where the scientist is actually right (subtle point)

The warning becomes valid if interpreted differently:

--> If India loses capability or momentum in thorium R&D, that would be strategic damage.

Because thorium leadership is one of India’s few unique advantages globally, no other country has pursued it this consistently.

So:

not “deploying immediately” → reasonable
neglecting long-term development → risky.

7. Connection to current SMR discussion
My earilear posts ties directly into this.

If India: develops PHWR-based SMRs, experiments with Th-based fuels in them then SMRs could become: bridges to thorium deployment



The NDTV article captures a real strategic truth, but expresses it too dramatically.

-- Correct: Thorium is crucial for India’s long-term energy independence

-- Overstated: India is not “abandoning” it

-- Reality: Thorium is technically complex and decades away from scale

I will say : Thorium is not India’s immediate energy solution—but it is likely its ultimate nuclear endgame, provided the fissile bridge (Pu/U-233) is successfully built.

https://x.com/Varun55484761/status/2036310088911298780
@Varun55484761
Bengaluru-based startup, Pranos Fusion, has developed a tiny tokamak device with a radius of just 40 cm. It has called it PRAGYA. It is India’s 1st privately developed tokamak & also the smallest.
PRAGYA is essentially a test bed designed as a precursor to a larger tokamak

^^^FWIW: Few comments:
Small(~40 cm device falls into this category ) tokamaks are not new and quite common in university labs worldwide for decades. So the form factor itself is not a breakthrough.

Basic physics of plasma physics ==> Fusion performance scales roughly with: Plasma volume, Confinement time and Magnetic field strength. ==> A 40 cm tokamak ( very low plasma volume) cannot realistically achieve net energy gain:
It’s a research / diagnostic platform, not a power device. Of course, it might still matter if they’ve done something novel, but the tweet (as typical on X) doesn’t provide enough details. The post does not mention details so it is difficult to judge. IMO, It is a nice lab device—not a fusion breakthrough. Without confinement and Q data, this is engineering demo, not energy tech.”