A Japanese power company restarted a nuclear reactor this week, the first to come back online since a March earthquake and tsunami in the nation. The March 11 disasters sparked a nuclear crisis and a backlash that postponed plans to reopen reactors shut down because of damage, inspections or unrelated technical problems. Kyushu Electric Power Co. said it has started generating electricity from the No. 4 reactor late Tuesday at the Genkai nuclear power plant in western Japan. The reactor was taken offline in October after technical problems. Company officials won approval from a local governor and a mayor to bring the reactor online, Japan's Kyodo news agency reported. Nuclear safety critics criticized the reopening, with the power company receiving more than 200 calls Tuesday from citizens who opposed the move. Another power company said it may have suffered a setback in its efforts to handle damaged nuclear reactors. Tokyo Electric Power Co. said Wednesday it detected the chemical element xenon in a nuclear reactor at the crippled Fukushima Daiichi nuclear power plant, a sign that nuclear fission may have occurred. The power company said it began injecting boric acid into the cooling system and has not seen a temperature change that would suggest nuclear fission has occurred. The reactor, No. 2, was one of several damaged in the wake of the historic March 11 disaster. Recently, Japanese officials said it may take 30 years to decommission the four damaged reactors at the power plant. A draft report, released by Japan's Atomic Energy Commission of the Cabinet Office last week, said the removal of debris -- or nuclear fuel -- should begin by the end of 2021.