To begin with India used un-enriched Uranium fueled Pressured Heavy Water Reactors (PHWR) for its nuclear power generation program, and fissile Plutonium-239, a byproduct of nuclear power generation, for its nuclear weapons program.

The impetus for Uranium enrichment came from the country's nuclear submarine project since nuclear submarines are generally powered using Light Water Reactors (LWRs) using enriched Uranium as fuel, since these reactors are safer.

India reportedly set up a pilot-scale Uranium enrichment plant at the Bhabha Atomic Research Center (BARC) in Mumbai in 1985.

In 1986 Indian Atomic Energy Commission Chairman Raja Ramanna announced that the country had successfully enriched Uranium.

The Department of Atomic Energy (DAE) commissioned a Uranium enrichment plant, codenamed the Rare Materials Project (RMP), around 1990 at Ratnahalli, about 19 kilometers from Mysore.

After initially facing technical difficulties, by 1997 India was successfully enriching Uranium at Ratnahalli.

According to the Global Fissile Material Report 2010, the Rattehalli facility has built three generations of uranium centrifuges.

The capacity at the end of 2009 was estimated 14,000 to 31,000 SWU/yr, enough to produce one or two submarine-reactor cores per year. 

By beginning of 2010, assuming 0.3 % depleted uranium tails, extrapolating the growth, it was estimated India was producing 0.2 to 0.5 tons of U-235 in HEU enriched to 30 to 45%.

The report estimated 2010 enrichment capacity and HEU stockpiles as being well beyond what would be required to operate a fleet of three nuclear submarines. 

Each submarines core is estimated to contain 70-kg of U-235, equivalent to 12,500 SWU based on the following published capabilities of the submarine class

Submarine displacement: 6000 ton

Max Speed: 25k

Reactor Power: 80-90 MWth

Fuel Enrichment: 30-45%

U-235 Content: 65-73kg

The original and probably still primary purpose of the Ratnahalli plant is to enrich uranium for nuclear-submarine fuel.

In October 2011, the Institute for Science and International Security released a Google Earth image that shows what appears to be a new uranium enrichment facility at Ratnahalli.

According to the accompanying ISIS report, the imagery, first noticed on February 28, 2011, suggests the new facility under construction is roughly 210 meters by 150 meters.

Earlier in October, Nuclear Intelligence Weekly reported that Bhabha Atomic Energy Centre Director R.K. Sinha had admitted that India was “building a new uranium enrichment facility” but it was unclear whether Mr. Sinha was referencing the RMP site or a planned new enrichment facility near the town of Chitradurga.

The new facility appears much larger than the approximately 130 meters by 130 meters existing facility, so if it is an enrichment facility, "it may house a greater number of centrifuges, giving India a larger enrichment capacity," says ISIS analyst Paul Brannan.

The discovery corroborates observations made based on procurement evidence in 2006, that India would soon add at least 3,000 gas centrifuges to its enrichment programme and that its uranium enrichment program would likely continue to expand, Mr. Brannan said. "A new gas centrifuge plant would indicate that the military uranium enrichment program is indeed expanding and that further procurement activities are likely ongoing," his paper noted.

During an interview with The Hindu in September 2010, , Srikumar Banerjee, Chairman, Atomic Energy Commission (AEC) and Secretary, Department of Atomic Energy (DAE), was asked:

He replied: Chitradurga will come a little later, not immediately. Our Ratnahalli plant capacity has been enhanced. But more than that, there is significant improvement in our technology. Usually, a term called Separating Work Units (SWUs) defines the technology level that we have achieved in this, and I can assure you that there has been considerable improvement in SWUs of our next generation caskets of centrifuges. The separating capacity of our centrifuges has improved. So total capacity enhancement at Ratnahalli has been done. We are confident of supplying the entire fuel for the set of….

You cannot say anymore that India does not have enrichment technology. India has its own technology and we can produce [enriched uranium]. We have not started doing it for large-scale commercial nuclear power stations, which require a much larger quantity of enriched uranium. We will be able to do that once we go to Chitradurga.

In an interview to CNN-IBN in December 2011, Dr Banerjee reitrated that India will have enough HEU from Ratnahalli to fuel its nuclear submarine fleet.

India is building a un-safeguarded enrichment facility at Chitradurga. The enrichment facility will be able to produce enough HEU to fuel 1,000 MWe nuclear power plants.

During his September 2010 interview referred above, Srikumar Banerjee was asked:

I will not be able to tell you now. The scheme is not yet ready. It should be able to feed enough enriched uranium to large-sized, 1,000 MWe nuclear power plants.

The following are excerpts Dr Srikumar Banerjee's December interview to Surav Jha of CNN-IBN.

Saurav Jha:Is your current enrichment capability sufficient to fuel India’s emerging nuclear submarine fleet or will that be attained only with Chitradurga? If not then will Chitradurga be used only for civilian power reactors?

Dr Srikumar Banerjee: Our existing site is more than adequate for feeding the fleet. And this fleet is of course more than one.

As far as the new facility in Chitradurga is concerned, it will not be a safeguarded facility. We are keeping the option open of using it for multiple roles.

Chitradurga could of course be used to produce slightly enriched uranium (SEU) with about 1.1 per cent U-235 content to fuel our pressurized heavy water reactor (PHWR) units which would boost the fuel burn-up to as much as 20000 MWd/ton.

Saurav Jha:That is almost half of what new generation light water reactor technology is achieving and quite impressive.

Dr Srikumar Banerjee: Yes.

Saurav Jha:Will Chitradurga also be used to create enriched uranium for powering DAE’s own indigenous 700 MWe Light Water Reactor(LWR) design which it plans to roll out by 2020?

Dr Srikumar Banerjee: Yes, that option is always there.

Saurav Jha:Has this indigenous design grown out of the work DAE has done for India’s nuclear submarine project?

Dr Srikumar Banerjee: Well a lot of work has been put into developing the 700 MWe LWR. In any case you would note that pressurised water reactor designs worldwide have essentially grown out of naval propulsion units.

Saurav Jha:So that brings us to our next question. Have our ENR technologies matured enough to be regarded as commercial grade?

Dr Srikumar Banerjee: Well in the case of reprocessing, certainly. We may yet not be setting up reprocessing plants as big as Rokkasho in Japan or Sellafield in UK but the new reprocessing facilities that are slated to come up in the next decade or so are going to be appreciably bigger than what we have now. Even the one that is nearing completion in Kalpakkam is a fairly large facility.

The planned integrated nuclear recycle plant for instance will be handling close to 500 tonne/year of heavy metal and will be sited at Tarapur which is in one of our existing sites. During the next plan period we will look at two more such facilities.

Talking about enrichment, we are quite happy with the progress we are making and with the new Chitradurga facility we are closing in on what you could refer to as industrial level capability. Again, this won’t be as big as the largest out there but it would be substantial.