Japan's Kansai Electric Power Co. manually shut down the No.1 reactor at its Ohi nuclear power plant in western Japan's Fukui Prefecture due to technical glitches with its cooling system Saturday, local media reported.

No radiation leakage had occurred and the problem will not have adverse effects on the environment, according to Japan's Nuclear and Industrial Safety Agency.

The pressure inside the accumulator in the reactor's emergency core cooling system temporarily fell on Friday night, setting off an alarm. The accumulator holds coolant to be injected into the reactor in an emergency, Kyodo News said.

The pressure has stabilized since, but the utility halted the reactor Saturday night to find out what caused the problem.

The reactor has been undergoing final adjustment procedures prior to commercial operations for an unusually long period of about four months. The 1,180,000-kilowatt reactor is equivalent to around 4 percent of the total power output of Kansai Electric.

Kansai Electric President Makoto Yagi issued a statement, saying, "We will make utmost efforts to secure additional supply capacity to prevent a situation that leads to a blackout."

The utility is expected to ask for more power saving measures from the public and industries due to the accident, while securing supplies from other utilities, watchers said.

The Ohi reactor, one of 19 that remain active across Japan after the March twin disasters of quake and tsunami which prompted the world's worst nuclear crisis in two decades, operated at near full capacity for much of the adjustment phase, including at the time the accident occurred Friday night.