A second storage pool was leaking highly radioactive water at the crisis-stricken Fukushima Dai-chi nuclear plant on April 7, operator Tepco said.
About 120 tonnes of radioactive water breached the inner lining of one underground storage pool on April 5, with concerns that some may have leaked into the soil.
Tepco is moving the remaining 13,000 tonnes of water in that tank to other pools, but said the April 7 leak was not large enough to warrant doing the same.
The leaks will pile more pressure on Tepco, which already is already red-faced over a string of power cuts at Fukushima. There was a two-hour power cut on April 5 at one of the storage pools for spent fuel rods.
The company claims it takes two weeks for an outage to become dangerous, but if the water runs dry the fuel rods will spew out huge amounts of radiation.
The outage followed a much longer blackout last month caused by a rat crawling across a control terminal kept in the back of a truck outside.
The company announced just days before the latest leaks that its president, executive vice-president and managing executive officer would all have 5% of their April pay packets docked over their poor handling of the outage.
Tepco spokesperson Masayuki Ono said the leaks were not only an immediate environmental problem but threatened the tight water-management situation.
Tepco has been forced to build hundreds of temporary storage tanks. Ono said the company hoped to release the water into the ocean but would not do so without public acceptance.
An earthquake and tsunami triggered multiple meltdowns at Fukushima in March 2011, forcing the evacuation of about 160,000 people who still do not know if and when they will be allowed to return home.
[Abridged from .]