MOSCOW, July 18 (RIA Novosti) - The operator of a Japanese nuclear power plant admitted that a radiation leak into the sea following Monday's earthquake was 50% worse than initially reported, a national news agency said.

Kyodo news agency quoted Tokyo Electric Power Co. (TEPCO) as saying its experts had miscalculated the amount of radioactive water that leaked from a power unit at the Kashiwazaki-Kariwa plant, 135 miles northwest of Tokyo, but insisted that the amount was still well below allowable limits.

The 6.8-magnitude quake struck early Monday killing nine residents of the nearby city of Kashiwazaki, and TEPCO reported later in the day that about 1,200 liters (315 gallons) of radioactive water had escaped from a reactor containment building.

On Tuesday, it said that a damaged exhaust stack had also accidentally discharged cobalt-60 and chromium-51, while barrels containing low-level radioactive waste had tipped over.

In all, the company said the plant, the world's largest in terms of output, suffered damage at 50 separate points, including a crack in the plant's foundation, raising general questions regarding the safety of nuclear power plants in the earthquake-prone nation, and prompting a government order forbidding the plant from restarting until appropriate checks are conducted.

Although the plant's emergency system automatically shut down the four power units operating when the tremor hit, a fire that ignited a short time later in the plant's third unit was not contained for three hours, with firefighters reporting inadequate water pressure to effectively combat the blaze.

Japanese experts and officials quickly raised concerns as news of the leak spread; even though it was discovered at around noon Monday, it took until about 6:00 p.m. for the company to confirm that the water was radioactive.

The government was not informed until an hour later, and the public did not learn of the incident until nearly 10:00 p.m.

Japan, which relies heavily on atomic energy to power its economy, has 55 working reactors, most of which were built to more lax specifications, and are able to withstand earthquakes measuring just 6.5 on the Richter scale.

Coincidentally, a review had been launched last September with the aim of raising that standard to 6.9, but Monday's quake has already led some experts to demand the government set even stricter requirements.

Despite plans to rely on nuclear power for up to 40% of its energy needs by 2010, Japan's nuclear industry has been plagued by accidents and scandals involving safety cover-ups.

In 2004, a ruptured steam pipe at the Mihama Nuclear Power Plant in western Japan killed five workers and injured six, and in 1999 an accident at a reprocessing plant killed two and exposed hundreds to radioactive contamination.