The operator of Japan's stricken nuclear plant said Wednesday that it had apparently contained at least one leak that was allowing radiation to seep into the sea.

Tokyo Electric Power Co. had said Tuesday that it had found iodine-131 at 7.5 million times the legal limit in a seawater sample taken near the facility, and government officials instituted a health limit for radioactivity in fish. Other samples were found to contain radioactive cesium at 1.1 million times the legal limit.

The exact cause of the radiation was not immediately clear, though Tepco has said that highly contaminated water has been leaking from a pit near the No. 2 reactor. The utility had suspected that the leak was coming from a crack, but several attempts to seal the crack failed to stop the flow.

On Tuesday the company said the leak might instead be coming from a faulty joint where the pit meets a duct, allowing radioactive water to seep into a layer of gravel underneath. The utility injected "liquid glass" into the gravel, and on Wednesday officials were reporting that the leak had been contained.

Meanwhile, Tepco continued releasing what it described as water contaminated with low levels of radiation into the sea to make room in onsite storage tanks for more highly contaminated water. In all, the company said it planned to release 11,500 tons of the water, but by Tuesday morning it had released less than 25% of that amount.

Although the government authorized the release of the 11,500 tons and has said that any radiation would be quickly diluted as it dispersed in the ocean, fish with high readings of radioactive iodine are being found.

On Monday, officials detected more than 4,000 becquerels of iodine-131 per kilogram in a fish called a sand lance caught less than three miles offshore from the town of Kitaibaraki, about 50 miles south of the Fukushima Daiichi nuclear complex. The fish also contained 447 becquerels of cesium-137, which is considered more problematic than iodine-131 because it has a much longer half-life, which means it takes longer to decay.

On Tuesday, Chief Cabinet Secretary Yukio Edano said the government was imposing a standard of 2,000 becquerels of radioactive iodine per kilogram of fish, the same level it allows in vegetables. Previously, the government did not have a specific level for fish.

Fishing of sand lances has been suspended. Local fishermen demanded that Tepco compensate them for their losses.

Fishing has been banned near the nuclear plant, and the vast majority of fishing activity in the region has been halted because of damage to boats and ports by the March 11 earthquake and tsunami. Still, some fishermen are out making catches, only to find few buyers because of fears about radiation.

It was unclear what Tepco might offer the fishermen, but the company said Tuesday that it would be giving "condolence payments" totaling about $2 million to residents who had to evacuate their homes because of radiation from the Fukushima plant. One town, however, refused the payment.

The company has yet to decide how it will compensate residents near the plant for damages, though financial analysts say the claims could be in the tens of billions of dollars. Tepco's executive vice president, Takashi Fujimoto, said the company's decision on damages hinges on how much of the burden the government will share.

Edano, the government spokesman, urged the company to accelerate its decisions on compensation.

For now, Fujimoto said, the company has offered $240,000 to each of 10 villages, towns and cities within 12 miles of the plant, the area in which the government has ordered residents to evacuate.

"We hope they will find it of some use for now," he said.

Namie, a town of 20,600 about six miles north of the plant, refused the money. Town official Kosei Negishi said he and other government officials were working out of a makeshift office in Nihonmatsu, elsewhere in Fukushima prefecture, and that they faced more pressing issues.

"The coastal areas of Namie were hit hard by the earthquake and the tsunami, but because of the radiation and the evacuation order, we haven't had a chance to conduct a search for the 200 people who are missing," Negishi said. "Why would we use our resources to hand out less than 1,000 yen [$12] to every resident?"

Tepco's Fujimoto acknowledged that there was a "gap" in the views of company and Namie officials.

julie.makinen@latimes.com

Hall is a special correspondent.