The old units are Mystic 4, 5 and 6 and New Boston 1, all in Massachusetts. Exelon decided to retire these oil- and gas-fired units, built between 1957-65, as it completes Mystic 8 and 9, two new 800MWe gas-fired units. Mystic 8 began operating in April 2003, and Mystic 9 is expected to start in June 2003.
