Workers struggle to plug leak at Japan nuclear plant

Tokyo (CNN) — Highly radioactive water continued leaking Sunday from the Fukushima Daiichi nuclear power facility directly into the Pacific Ocean, following a failed attempt to plug a cracked concrete shaft, a utility company official said.

Authorities said Saturday that they had discovered water gushing out of a two-meter-deep, concrete-lined basin and into the sea via a roughly 20-centimeter (8-inch) crack. The shaft sits behind the No. 2 reactor’s turbine building at the facility, which has been in constant crisis since the failure of cooling systems and numerous explosions in the wake of last month’s epic earthquake and tsunami.

Later that day, power plant workers tried — unsuccessfully — to fix the leak by pouring in fresh concrete, Tokyo Electric Power Company officials said late Saturday.

Now, they are on to “Plan B.” The company planned to decide what type of polymer — a synthetic compound — would be used to fill the crack. Workers will then break the shaft’s ceiling and insert the polymer in a different spot from where they tried to place the concrete, the utility’s officials said. That phase hadn’t started as of late Sunday morning, said Hidehiko Nishiyama of Japan’s nuclear and industrial safety agency.

Radiation levels in the affected shaft itself measured at more than 1,000 millisieverts per hour, which is more than 330 times the dose an average resident of an industrialized country naturally receives in a year. Above, the level was 250 millisieverts per hour. The shaft lies at the end of a long channel that has been filling up for days.

Fixing the problem quickly is critical because officials believe it is one source of alarmingly high levels of radiation spotted in seawater near the plant.

Last Thursday, samples of seawater taken 330 meters (361 yards) offshore were said to have levels of iodine-131 at 4,385 times above the standard and cesium-137 at 527 times beyond normal. Experts say the latter radioactive isotope may be a greater concern because it persists longer, taking 30 years to lose half its radiation — compared to an eight-day half-life for the iodine-131 isotope.

Plugging the external leak is job one, in order to prevent the immediately outflow of radiation into the Pacific. But it may not be the most difficult, or important, task ahead.

Authorities still have to figure out how the tainted water got into the concrete shaft — with 1,000 millisieverts per hour of radiation, which is more than 330 times the dose an average resident of an industrialized country naturally receives in a year — in the first place. That water had to come from somewhere, potentially coming across melted down nuclear fuel in the reactor’s core before somehow reaching the outside.

Nishiyama, the nuclear safety official, said the working theory is that water injected in recent weeks into the No. 2 reactor to help cool its nuclear fuel rods somehow got out.

“We were assuming and hoping (that water) would stay in the containment vessel as vapor after being cooled,” he said. “However, it may have flowed into the building, and then the trench.”

Finding out why and how that happened — and, more so, what to do about it — promises to be “exceptionally challenging,” said physicist James Acton, with the Washington-based Carnegie Endowment think tank.

To do so, officials must inspect a complicated array of pipes inside the dangerous radioactive environment that now exists within the containment building, according to Acton, familiar with Japanese nuclear plants in part from having examined one another rocked by a 6.8-magnitude earthquake in 2007.

This struggle is part of the larger, daunting challenge facing Tokyo Electric and Japanese officials as they come to grips with the scope of the disaster and also work feverishly to keep nuclear fuel cool and prevent the further release of dangerously radioactive material.

The human cost of the natural disasters became starkly apparent Sunday, when a power company official announced two workers missing since the 9.0-magnitude March 11 quake were found dead in the basement of the No. 4 reactor’s turbine building. Both men, ages 21 and 24, appeared to have suffered multiple traumatic injuries. Their remains were found Wednesday.

More than a dozen others have been reported injured over the past three weeks, most of them tied to explosions in the Nos. 1 and 3 reactor complexes tied to the buildup of hydrogen. To prevent this from happening again, Nishiyama said there is a plan to inject nonflammable nitrogen into the Nos. 1, 2 and 3 reactors to prevent another such hydrogen blast.

A buildup of hydrogen is an early sign of damage to a reactor’s superheated core. But Nishiyama said no alarms had been sounded about rising pressure and that adding nitrogen would not force engineers to release hydrogen from the reactors.

Meanwhile, efforts continue to assess the amount and impact of radiation that has already escaped.

That includes spraying an experimental synthetic resin to lock in radioactive material on the ground, so it can’t interfere with restoring cooling systems aimed at preventing the overheating of nuclear fuel in reactors and spent fuel pools.

Also, Jeff Immelt, the chief executive of General Electric Co., was heading to Japan to meet with Tokyo Electric authorities about stabilizing the damaged reactors, company spokeswoman Deidre Latour said Saturday. Several of the Fukushima Daiichi plant’s reactors were designed by GE.

All these difficulties notwithstanding, there has been good news recently on the nuclear front.

Figures released this weekend by Japan’s health and science ministries showed levels of radioactive iodine and cesium in vegetables tested in Fukushima and Niigata prefectures had fallen below legal limits.

Still, there was no immediate indication that officials would lift restrictions on the sale and distribution of certain products from areas near the stricken plant, put in place after tests detected high radiation levels in some food.

CNN’s Tsukushi Ikeda, Yoko Wakatsuki, Junko Ogura, Midori Nakata and Susan Olson contributed to this report.