Nuclear installations across the country have been put on high alert as it has been found that David Headley, a US citizen arrested by FBI on terror charges, had visited these places. Sources in the Home Ministry said on Monday that all the states having nuclear plants have been asked to step up patrolling and vigil around the facilities as a precautionary measure.<br/>Headley, accused of plotting terror attacks in India on behalf of Pakistan-based LeT, had visited Gujarat, Maharashtra and Uttar Pradesh all having crucial nuclear installations , raising suspicion that nuclear facilities could be on the radar of the terrorists.<br/>AIR correspondent reports,there are six major nuclear energy plants operational in the country, Narora in Uttar Pardesh, Kaiga in Karnataka, Tarapur in Maharashtra, Kalpakkam in Tamil Nadu, Kakrapar in Gujarat and Kota in Rajasthan, besides several other Research and Development centres like Bhabha Atomic Research Centre in Trombay. <br/>