A Japanese nuclear power plant - the world's biggest - may be shut down for more than a year while a safety study is made after an earthquake caused radiation leaks and showed that the plant was built above an active fault.

Fears about the safety of Japan's nuclear industry have been renewed by radiation leaks into the ocean and atmosphere from Tokyo Electric Power Co.'s (TEPCO) plant in the northwestern city of Kashiwazaki, hard hit by a 6.8 magnitude quake on Monday.

The trade minster and a local mayor have already said the Kashiwazaki-Kariwa plant, closed since the quake that flattened homes and killed 10 people, cannot reopen until safety is assured.

On Thursday, the Nikkei business newspaper said the government might order Tepco to keep the plant shut for more than a year while a safety study is conducted, raising questions about possible power cuts and the hefty cost to Tepco of firing up other mothballed power stations to meet heavy summer demand.

If the earthquake resistance study shows the facility needs to be reinforced, it might take much longer than a year before operations can resume, the newspaper added.