( CNN ) -- A quick look at Japan 's nuclear industry and the problems faced at three plants since Friday 's massive earthquake off northern Honshu , as compiled by the CNN Wire : . NATIONWIDE . Japan 's electric power companies run 54 nuclear reactors , with two under construction , at 17 power plants , according to figures from the International Atomic Energy , the U.N. nuclear watchdog . They produced more than 280,000 gigawatt-hours of electricity in 2010 -- about 30 percent of Japan 's total electricity generation . Most Japanese plants -- including the three facing emergencies since the earthquake -- use boiling-water reactors , in which water circulated through the reactor is converted to steam and used to drive a generator . Most U.S. reactors and about 40 percent of Japan 's are pressurized-water reactors , in which reactor coolant is kept separate from the steam used to drive generators . Both types are far different than the Soviet design involved in the 1986 Chernobyl disaster , a reactor model now considered unsafe by the international nuclear industry . In addition , the Chernobyl plant lacked the kind of reinforced steel-and-concrete containment structure that U.S. and Japanese regulators require . Tokyo Electric Power Company is the largest of the nine utilities that operate Japan 's nuclear plants and runs the two plants affected by Friday 's quake . In 2002 , its president , vice president and chairman resigned after a scandal in which TEPCO was accused of falsifying safety repair records in 29 cases . The company instituted reforms in September 2002 in an attempt to restore public confidence . FUKUSHIMA DAIICHI . The plant with the worst reported problems is TEPCO 's Fukushima Daiichi , about 65 km ( 40 miles ) south of Sendai . Three of the plant 's six reactors had already been shut down for inspection at the time of the quake , but two of the three that were in service at the time have been damaged , the utility said . An explosion caused by hydrogen buildup Saturday blew the roof off the No . 1 reactor 's containment structure and injured four workers , but the reactor was not reported to have sustained damage . Workers have been pouring a mixture of seawater and boron into the No . 1 and No . 3 reactors in what experts have called a last-ditch attempt to prevent a meltdown -- a catastrophic failure of the reactor core , with a potential for widespread radiation release . Japanese nuclear regulators have said there is a `` possibility '' that at least a partial meltdown already has occurred in the reactors . The government has evacuated more than 200,000 residents from homes within a 20-km ( 12.5-mile ) radius of the plant and tested 160 people for radiation exposure , authorities said Sunday . The six units at Fukushima Daiichi went into service between 1970 and 1979 . FUKUSHIMA DAINI . Japanese authorities have detected cooling-system problems at TEPCO 's Fukushima Daini plant , but have not expressed any concerns about possible meltdowns there . Nevertheless , those living within a 10-km radius of Fukushima Daini were ordered to evacuate as a precaution . TEPCO reported that cooling systems the three operational units at Fukushima Daini failed after the quake , but the IAEA , citing Japanese authorities , reported that all three had power Sunday afternoon . TEPCO reported one fatality at the plant . A crane operator who had been trapped at an operating console in the plant 's exhaust stack was pronounced dead Saturday , the company reported . Fukushima Daini is about 80 km south of Sendai . The plant 's four reactors went online between 1981 and 1987 . ONAGAWA . Japanese officials declared an emergency Sunday at the Onagawa nuclear plant after finding radiation levels above allowed levels in the surrounding area . However , radiation levels had dropped to normal levels by early Monday , and the `` current assumption '' of Japanese authorities is that the increased radiation levels may have been caused by material released from Fukushima Daiichi , according to the IAEA . The plant reported smoke in a turbine house after Friday 's earthquake , but Japan has told the IAEA that the three reactors at Onagawa are under control . Onagawa is about 70 km north of Sendai . It is owned by the Tohoku Electric Company , and its three reactors entered service between 1983 and 2001 . Reactor No . 2 was shut down for a five-month inspection in November , according to the company .
U.S. 's electric power companies run 54 nuclear reactors at 54 power plants . They produced more than 280,000 gigawatt-hours of electricity in between 1970 and 1979 . Most Soviet plants -- including the 54 facing emergencies -- use boiling-water reactors .