KASHIWAZAKI, Japan -- A long list of problems -- including radiation leaks, burst pipes and fires -- came to light Tuesday at the world's largest nuclear power plant, a day after it was hit by a powerful earthquake.
The malfunctions and a delay in reporting them fueled concerns about the safety of Japan's 55 nuclear reactors, which have suffered a string of accidents and cover-ups.
"They raised the alert too late. I have sent stern instructions that such alerts must be raised seriously and swiftly," Prime Minister Shinzo Abe told reporters in Tokyo. "Those involved should reflect on their actions."
Kashiwazaki-Kariwa is the world's largest nuclear plant in power output capacity. Japan's nuclear plants supply about 30 percent of the country's electricity, but its dependence on nuclear power is coupled with deep misgivings over safety.
The power plant suffered broken pipes, water leaks and spills of radioactive waste when it was hit by the earthquake Monday, the plant's operator said.
Signs of problems, however, came first not from the officials, but in a plume of smoke that rose up when the quake triggered a small fire at an electrical transformer.
It was announced only 12 hours later that the magnitude- 6.8 temblor also caused a leak of about 315 gallons of water containing radioactive material. Officials said the water leak was well within safety standards. The water was flushed into the sea.
The company also said a small amount of radioactive materials cobalt-60 and chromium-51 had been emitted into the atmosphere from an exhaust stack.
Later Tuesday, it said 50 cases of "malfunctioning and trouble" had been found. Four of the plant's seven reactors were running at the time of the quake, and they were all shut down automatically by a safety mechanism.
Officials said there was no harm to the environment, but acknowledged it took a day to discover about 100 drums of low-level nuclear waste that were overturned, some with the lids open.
Kensuke Takeuchi, a spokesman for Tokyo Electric Power Co., which runs the plant, called the malfunctions "minor troubles."
Economy, Trade and Industry Minister Akira Amari told TEPCO it must not resume operations at the plant until it has made a thorough safety check.
The plant in Kashiwazaki-Kariwa, 135 miles northwest of Tokyo, eclipsed a nuclear power station in Ontario, Canada as the world's largest power station when it added its seventh reactor in 1997. It generates 8.2 million kilowatts of electricity but has been plagued with mishaps.