More than a decade of nationwide hunt for a safe long-term nuclear waste repository has narrowed the search to these two states, said K Balu, director of the nuclear recycle group at BARC.

`We are in stage-2, where we have identified in these states 100 square kilometre areas suitable for burying the wastes,' said Balu.

`In stage-3, we will close in on an area of just five square km, he said. Right now drilling is going on in Rajasthan.'

Balu said selection of sites with stable geological granitic rocks deep underground involved co-operation of agencies such as Geological Survey of India (GSI).

He said that a vault dug out in granitic rocks 800 metres below the ground will hold all the wastes from India's nuclear facilities. An area of no more than one square km would be needed to set up the repository, he said.

According to Balu,there will be absolutely no chance of radioactivity escaping from the vault because of `multiple barriers'.

First, the radioactive atoms are embedded in tough, boro-silicate vitrified glass. `Each glass block is enclosed by a stainless steel box, and two such boxes will be put inside another stainless steel box welded on all sides, and stacked in the vault which will be instrumented with equipment to monitor radiation and temperature,' Balu said.

Balu said India has been ahead of several other countries in the search for permanent storage site. The United States launched the hunt 15 years ago.

He said there is no urgency to build the waste repository because the quantity of nuclear wastes generated by India is small. Furthermore, the vitrified glass blocks, in which the radioactive wastes are held, must be stored in water for at least 25 years before burial.

One such storage facility is operating in Tarapur and another is to be built in Kalapakkam by 2002.

The underground site to be chosen forpermanent burial will be far from any ground water source, mineral bearing areas and populated regions, Balu said.