The Exelon Corporation, the largest US operator of nuclear power plants, made an unsolicited offer to buy rival NRG Energy Inc. for $6.2 billion. In a letter to NRG president and chief executive office David Crane and chairman Howard Cosgrove, Exelon proposed to acquire all of NRGÔÇÖs outstanding common stock in an all-stock transaction. The deal would create the largest power company in the US, worth about $60 billion and with a generating capacity of about 47,000 megawatts, enough electricity to serve nearly 45 million homes, according to Exelon. Chicago-based Exelon is one of the nationÔÇÖs largest electric utilities, with nearly $19 billion in annual revenues. It owns and operates 17 nuclear reactors, including Three Mile Island in Pennsylvania. Its strength is in the Midwest and Middle Atlantic. Acquiring NRG would provide Exelon with nuclear stations beyond its Illinois and Pennsylvania bases. Princeton, New JerseyÔÇôbased NRG is the second-largest electricity generator in Texas and also has plants in California, Connecticut, Louisiana and New York. Exelon said one advantage of the deal would be an enormous combined entity with the financial resources to build new power plants. Demand for nuclear power is growing, driven by oil price volatility and attempts to reduce greenhouse gas emissions. But the resurgence of nuclear power is being held back by the current credit crisis. NRGÔÇÖs board said it plans to review ExelonÔÇÖs proposal and ÔÇ£determine the appropriate response in due course.ÔÇØ It advised its stockholders to take no action at this time. ┬á┬á┬á┬á