A utility in Missouri said Thursday that it was suspending its efforts to build a new nuclear reactor, making its proposed plant, Callaway 2, the first of the so-called nuclear renaissance reactors to fall by the wayside. The industry has been looking forward to its first construction start in 30 years. According to the Nuclear Regulatory Commission, 17 companies have filed applications to build 26 reactors. The utility, AmerenUE, planned to build a reactor near Fulton, Mo., but was seeking changes in the state law governing the financing of new power plants. In a letter on Thursday, it asked the sponsors of a law now moving through the state legislature to withdraw the measure. AmerenUE wanted to be allowed to charge its customers for financing costs before the plant was finished. In its current form, the law that did not include that provision, which the company said made