At least 45 tons of highly radioactive water have leaked from a purification facility at the Fukushima Daiichi nuclear power station, and some of it may have reached the Pacific Ocean, the plant's operator said on Sunday.

Nearly nine months after Fukushima Daiichi was ravaged by an earthquake and tsunami, the plant continues to pose a major environmental threat. Before the latest leak, the Fukushima accident had been responsible for the largest single release of radioactivity into the ocean, threatening wildlife and fisheries in the region, experts have said.

The new radioactive water leak called into question the progress that the plant's operator, Tokyo Electric Power Company, appeared to have made in bringing its reactors under control. The company, known as Tepco, has said that it hopes to bring the plant to a stable state known as a cold shutdown by the end of the year.

The extent; risks

The trouble on Sunday came in two stages, a Tepco statement said. In the morning, utility workers found that radioactive water was pooling in a catchment next to a purification device; the system was switched off, and the leak appeared to stop. But the company said it later discovered that leaked water was escaping, possibly through cracks in the catchment's concrete wall, and was reaching an external gutter. In all, as much as 220 tons of water may now have leaked from the facility, according to a report in the newspaper Asahi Shimbun that cited Tepco officials. The company said that the water had about one million times as much radioactive strontium as the maximum safe level set by the government, but appeared to have already been cleaned of radioactive caesium before leaking out. Both elements are readily absorbed by living tissue and can greatly increase the risk of developing cancer.

Since the disaster in March, workers have been struggling to cool the stricken plant's reactors by flooding them with water, which is contaminated with radioactivity in the process and becomes a problem of its own. Tepco installed a new circulatory cooling system in September with filters that decontaminate and recycle the cooling water. Thousands of tons of water remain in the flooded basements of the plant's reactor buildings.

The Institute for Radiological Protection and Nuclear Safety in France estimates that between March and mid-July, the amount of radioactive caesium 137 that had leaked into the Pacific from the Fukushima Daiichi plant amounted to 27.1 petabecquerels, the greatest amount known to have been released from a single episode. (A becquerel is a frequently used measure of radiation, and a petabecquerel is a million billion becquerels.) — New York Times News Service

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