(CNN) -- A reactor at Japan's Ohi nuclear plant will be shut down following problems with an emergency cooling system, Kansai Electric said Saturday.
The move follows an emergency alarm late Friday triggered when the pressure dropped in the tank for the cooling system, company spokesperson Masaki Todatake said.
Pressure returned to normal within about an hour after an injection of liquid nitrogen, but engineers plan to manually stop the No. 1 reactor at the Ohi plant in Fukui Prefecture to carry out a full inspection,Todatake said.
It is not known how soon the reactor might start operating again, the company said, but there is no danger of radiation leak.
The reactor's closure leaves only 18 of Japan's 54 nuclear plants producing electricity, worsening power supply problems following March's earthquake and tsunami.
The 15-meter (48-foot) tsunami inundated Japan's coastal Fukushima Daiichi power plant, leading to a triple meltdown, the aftermath of which Tokyo Electric Power Co. engineers are still struggling to manage.
The disaster has caused Japan to rethink its commitment to nuclear energy.
Journalist Chie Kobayashi contributed to this report.