The tropical beaches of India probably bring to mind sun-dappled palms, fiery fish curries and dreadlocked backpackers, but they also hold a surprising secret. Their sands are rich in thorium – often hailed as a cleaner, safer alternative to conventional nuclear fuels.

The country has long been eager to exploit its estimated 300,000 to 850,000 tonnes of thorium – quite probably the world’s largest reserves – but progress has been slow. Their effort is coming back into focus amid renewed interest in the technology. Last year Dutch scientists fired up the first new experimental thorium reactor in decades, start-ups are promoting the technology in the West and last year China pledged to spend $3.3bn to develop reactors that could eventually run on thorium.

Proponents say it promises carbon-free power with less dangerous waste, lower risk of meltdowns and a much harder route to weaponisation than conventional nuclear. But rapid advances in renewables, a costly development path and question marks over how safe and clean future plants would really be mean its journey to commercialisation looks uncertain.

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India’s pursuit of thorium is driven by unique historical and geographic conditions, which have given it considerable staying power. Some see a quixotic quest unlikely to live up to its promise, but the country’s nuclear scientists see a long-term strategy for carbon-free energy security in a country whose population could peak at 1.7 billion in 2060.

“We are a power hungry nation,” says Srikumar Banerjee, secretary of India’s Department of Atomic Energy (DAE) until 2012. “Eventually we need to rely on indigenous raw materials for the long-term sustainability of a country which is going to support one fifth of humanity.”