New Delhi, March 1 :    New Delhi, March 1:  The opponents of the sale of Bharat Aluminium Company (Balco) have found more fodder. The public sector unit possesses technology that was used in the country's nuclear and defence projects - its sale would thus go against the nation's 'strategic interests'. Through the 1990s, Balco's research metallurgists worked on a top secret project along with scientists from the Defence Research and Development Organisation (DRDO) and the Indian Space Research Organisation (Isro) to develop special lightweight aluminium alloys. These were used in India's nuclear armaments, the Prithvi and Agni series of intermediate missiles and for rocket components. When India tested nuclear bombs in 1998, Balco supplied the casings. It also makes and supplies the fuel tanks for Agni and Prithvi missiles as well as an alloy codenamed Afnor 7020 used by Isro in its rockets. Documents show that Balco is bound by a supply and production agreement with the Department of Defence Supplies to keep this technology secret. Sale of majority stake in Balco to a private sector company would violate this agreement. As part of the agreement - S.No 1(3)/90/T(S1)/CPO(VG)-1645 - Balco is bound to keep secret the alloy knowhow. Also, the agreement swears to secrecy not only the metallurgists who helped develop the alloys but also all scientists, engineers, other officers and technical hands who came to know about the technology, its use or manufacture. It is argued that selling Balco to the private sector could result in the technology being leaked to outsiders. The corollary being that Balco has to remain in the public sector. The clauses were inserted in the pact as the technology Balco has jointly developed makes India one of the few nations and possibly the only Asian country besides China to possess such knowhow. The work on these alloys did not fetch much money but was done because the defence ministry had picked Balco as its strategic partner. There were two reasons why Balco was selected and not Nalco, the other public sector aluminium major. First, Balco has a hot roll aluminium mill, needed to cast these alloys. Second, the location of Balco's plant - at Korba in Chhattisgarh - makes it safe from possible missile attack by Pakistan and China, the plant being some thousand miles distant from both the countries. It is also far from the coast, which rules out a surface-to-surface missile attack from an enemy ship. The technology that Balco developed is considered complex and difficult to replicate. None of the countries that India approached to buy it from - France and Russia among them - was willing to sell either the technology or the product. The fact that Balco is privy to such a technology makes it a strategic company, argue many. The BJP government's stated policy is to sell only non-strategic PSUs, not strategic ones. Trinamul Congress chief Mamata Banerjee is believed to have raised this point in a letter to Prime Minister Atal Bihari Vajpayee after the Union Cabinet cleared a proposal last year to sell 51 per cent in Balco to a private partner. Vajpayee had reportedly fought shy of a direct answer.