TOKYO - Workers at Japan's tsunami-damaged nuclear power plant on Wednesday finally halted a leak that was sending a tide of radioactive water into the Pacific and exacerbating concerns over the safety of seafood, the operator said.
It was a rare bit of good news for the Fukushima Dai-ichi complex and the coastal areas surrounding it, where high levels of seawater contamination have angered fishermen and prompted the government to set limits for the first time on the amount of radiation permitted in fish.
But in a sign that workers still face several challenges before the overheating reactors are stabilized, Tokyo Electric Power Co. said it plans to inject nitrogen gas into one of the reactors. Nitrogen can prevent highly combustible hydrogen from exploding as it did three times at the compound in the early days of the crisis.
There is no immediate possibility of an explosion, but the "nitrogen injection is being considered as a cautionary measure," said spokesman Hidehiko Nishiyama of Japan's Nuclear and Industrial Safety Agency.
TEPCO said the process could begin as early as Wednesday evening in Unit 1 where pressure and temperatures are the highest according to spokesman Junichi Matsumoto. The same measures will eventually be taken at the other two troubled reactors.
The 9.0-magnitude earthquake and tsunami that followed are believed to have killed as many as 25,000 people. Hundreds of miles (kilometers) of coastline have been destroyed and the country's fishing industry devastated.
Since the crush of water flooded the plant and knocked out cooling systems, workers there have been desperately trying to cool overheated reactors. The effort has required spraying large amounts of water and allowing it to gush out wherever it can escape, sometimes into the sea.
While officials have said the crack in a maintenance pit plugged early Wednesday was the only one found, they have not explicitly ruled out that radioactive water is leaking into the sea from another point.
"Right now, just because the leak has stopped, we are not relieved yet," said Chief Cabinet Secretary Yukio Edano. "We are checking whether the leak has completely stopped, or whether there may be other leaks."
Over the past few days, workers have tried concrete, polymer, sawdust and shredded newspapers in their efforts to seal the crack. All failed.
On Wednesday morning, TEPCO spokesman Naoki Tsunoda said an injection of 400 gallons (1,500 liters) of "water glass," or sodium silicate, and another agent appeared to be successful.
While photos of water pouring from the pit over the weekend intensified fears of ocean contamination, authorities had insisted the radioactive water would dissipate and posed no immediate threat to sea creatures or people who might eat them. Most experts agreed.
Still, Japanese officials adopted the new standards as a precaution. And the mere suggestion that seafood from the country that gave the world sushi could be at any risk stirred worries throughout the fishing industry.
"Even if the government says the fish is safe, people won't want to buy seafood from Fukushima," said Ichiro Yamagata, a fisherman who fled his home in the shadow of the power plant and now lives in an evacuation center near Tokyo. "We probably can't fish there for several years."
Fukushima is not a major fishing region, and no fishing is allowed in the immediate vicinity of the plant. But experts estimate the coastal areas hit by the massive wave last month account for about a fifth of Japan's annual catch.
The plugging of the leak does not end radiation concerns: Highly contaminated water continues to pool around the complex, about 140 miles (220 kilometers) northeast of Tokyo.
In an effort to make room in a storage facility for that water, the plant has been pumping 3 million gallons of less-contaminated water into the sea.
That measure angered local fishermen and a national association of fisheries groups, which handed a letter of protest to TEPCO's chairman on Wednesday.
"We have repeatedly asked the government and TEPCO to stop further radiation leaks into the ocean. But the government and TEPCO ignored us and dumped radioactive water into the sea, which is utterly outrageous," said the letter from Japan's largest fishermen's labor group. "What they have done is unforgivable. It could really destroy our business."
Fears of radiation contamination prompted India to announce Tuesday that it was halting food imports from Japan. Few countries have gone so far, but India's three-month ban reflected the unease created by the nuclear crisis among consumers. India said the ban would last three months or until the risk subsides. It planned to review the situation weekly.
The new limits on radioactivity in fish were imposed after TEPCO announced water tested near the leak coming from the plant Saturday contained levels of radioactive iodine 7.5 million times the legal limit. That level had dropped to 5 million two days later.
Japan said some fish caught last week about 50 miles (80 kilometers) from the plant would have exceeded the new safety limits, which may change as circumstances do.
The radiation standards for fish will be the same as for vegetables. After spinach and milk exceeded safety limits following the quake, health experts said people would still have to eat enormous quantities of tainted produce or dairy before getting even the amount of radiation contained in a CT scan.
Japan imports far more fish than it exports, but it sent the world $2.3 billion worth of seafood last year.
Some people were undaunted. At Sushizanmai, a sushi bar just outside Tokyo's famed Tsukiji fish market, customers were still eating Japan's famed raw fish delicacies Tuesday night.
But chef Seiichiro Ogawa said the fuss over radiation could hurt business. His restaurant is trying to get more fish from the western part of Japan, which has not been affected by the nuclear crisis.
"Japanese customers are especially sensitive to this kind of thing, so I'm worried they'll stop eating sushi," said Ogawa, who has already seen his business drop 50 percent after foreigners stopped visiting the city after the quake. "We need this nuclear problem to be resolved."