A nuclear reactor will be shut down in western Japan Wednesday because of cooling water valve troubles, its operator said.

Operations at the number two reactor of Mihama Nuclear Power Plant in Fukui will be suspended manually, said Kansai Electric Power, which runs the plant.

The company said it was still checking the cause of the trouble but did not believe there was any chance that cooling water would leak out of the plant.

No indication was given as to how long the reactor would be shut down.

Once the plant is suspended, only eight will remain in operation in Japan, amid fears over the safety of nuclear power in a resource-poor country that previously depended on the technology for around a third of its electricity needs.

The 9.0-magnitude quake and resulting tsunami on March 11 killed some 20,000 people and crippled cooling systems at the Fukushima Daiichi nuclear power plant, northeast of Tokyo, causing reactor meltdowns.

Subsequent explosions and radiation leaks forced the evacuation of tens of thousands of people from a 20 kilometre (12 mile) radius around the crippled plant, and in some pockets beyond.

Since the disaster at Fukushima, Japan has had to ramp up its imports of thermal fuels to plug the supply gap as the number of active reactors has dwindled amid stringent safety checks and local opposition to the technology.

A nationwide campaign to save energy over the summer has been extended over the winter, with continued warnings of a shortfall that could be particularly acute in western Japan, which is more heavily dependent on nuclear generation.