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Tuesday, March 29, 2011

Radioactive water keeps workers out

Turbine room floods linked to sea


By KAZUAKI NAGATA and KANAKO TAKAHARA
Staff writers

Reactor turbine basements flooded with highly radioactive materials kept a desperate effort to stabilize the Fukushima No. 1 power plant at bay Monday, as fresh data showed that nearby seawater was being contaminated further by the leaking facility.

Efforts by Tokyo Electric Power Co. to restore the cooling systems for reactors No. 1 through 4, as well as their spent-fuel storage pools, continue to be halted by the highly radioactive water, which is now at lethal levels.

Later in the day, Tepco said the strong radiation had been detected outside the turbine buildings as well, but in an area that could explain how the toxic material is contaminating the sea.

The latest discovery, confirmed Sunday, focuses on trenches below the turbine buildings of reactors No. 1, No. 2 and No. 3. Radiation as strong as 1,000 millisieverts per hour — the same as in the turbine room — was detected on the surface of water found in the trench below reactor No. 2.

The water in the trench below reactor No. 1 had a radiation level of only 0.4 millisieverts per hour.

Tepco said it could not monitor the radiation level in the trench below reactor No. 3 because there was too much debris there.

Since the trenches' exits are only about 55 to 70 meters from the sea, Tepco officials are worried that the highly polluted water could overflow from the trenches and out to the sea.

Experts say it is difficult to predict how long it will take to end the nuclear crisis.

Michiaki Furukawa, a board member of the nonprofit organization Citizens' Nuclear Information Center, said it may take even a month to pump out the toxic water, restore damaged cooling facilities and bring the nuclear reactors under control to end the crisis, which started with the March 11 earthquake and tsunami.

Eventually, the plant may need to be encased in concrete, like Chernobyl was, he said.

"Under that high amount of radiation, workers can probably work only up to 10 minutes at a time," said Furukawa, a professor emeritus on nuclear energy at Nagoya University.

But even if the radiation-polluted water is pumped out, its storage and disposal will remain a problem, he said.

"Water, or liquid, with high radiation can leak or spill. It's unstable," he said. "It's better to solidify it, but even then it is still problematic."

The water in the turbine building of reactor No. 2 is extremely contaminated, showing surface-level radiation in excess of 1,000 millisieverts per hour.

The limit for total radiation exposure set by the health ministry for each nuclear plant worker is 100 millisieverts, although the level has been raised to 250 millisieverts for the Fukushima plant workers, given the graveness and urgency of the crisis.

The water was believed contaminated by contact with partially melted fuel rods inside the No. 2 reactor's pressure vessel.

Highly radioactive materials in the pressure vessel should have been prevented from reaching the outside environment. The suspected failure thus poses a grave threat to workers at the plant.

At a news conference early Monday, Tepco said "the pipes of the pressure vessel and other components" might have been damaged and developed holes from which the water presumably exited the pressure vessel.

The National and Industrial Safety Agency, however, said later in the day it believes "the possibility is very low that there are some holes in the pressure vessel" itself.

Although it is unknown how much water has accumulated in each basement, Tepco said the maximum depth was 40 cm in the No. 1 reactor turbine building, 1 meter in that of reactor No. 2, 20 cm to 1.5 meters in No. 3, and 80 cm in No. 4.

Tepco needs to pump the toxic water into a container on the ground floor before it can resume repair work. But since that container is full, the utility has to route it to a separate tank.

Afterward, workers hope to scrub the basement to lower the radiation.

Although water in the No. 1 turbine building has been pumped into a condenser tank, Tepco has not yet come up with ways to remove the flooding at the other three turbine buildings.

Having been unable to find effective ways to move forward, Tepco appears to be visibly confused by the situation and has botched some of its announcements of crucial monitoring data.

Tepco erroneously announced Sunday morning that 2.9 billion becquerels of iodine-134 per cubic centimeter was detected from the water in the flooded turbine building of reactor No. 2 Saturday, a figure deemed 10 million times higher than what would typically be seen in a normal reactor.

But later the day, Tepco said the figure was wrong and had been based on a calculation involving data pertaining to a different substance. The correct figure is 19 million becquerels per cu. centimeter, or 100,000 times above the level in water in a normal reactor, according to Tepco.

Chief Cabinet Secretary Yukio Edano said he met with Tepco's vice president Monday and received an explanation about the information mixup.

"I understand workers at the site must be very exhausted, but this kind of monitoring result would be a major premise of securing safety," Edano told reporters in the morning. "I asked Tepco not to make the same mistake again."

Edano also said the Nuclear Safety Commission of Japan reported its analysis to him. It said the highly contaminated water in the No. 2 turbine building probably leaked directly from the containment vessel, although it is unclear how that occurred.

Also, monitoring data collected at 2:05 p.m. Sunday some 30 meters north of the drain outlets for the No. 5 and 6 reactor buildings detected radioactive iodine-131 levels in the seawater 1,150 times above the government standard.

The level from the same monitoring place was 202 times at 8:50 a.m. Sunday and 314 times at 2:50 p.m. Saturday.

Previously, the higher level of iodine-131 was detected at the south side. A reading of 1,250 times above the standard was detected at 8:30 a.m. Friday about 330 meters south of the drain outlets for the No. 1 and 4 reactor buildings, and it was 1,850 times at 2:30 p.m. on Saturday.

But the level had declined in the latest data collected, at 1:50 p.m. Sunday, to some 250 times above the standard.

Asked what the rising figure in the north and the decrease in the south indicates, "there are various possibilities, and it is possible that the contamination flowed from south to north," a Tepco official said during a press briefing around noon.

If someone drank 500 ml of water containing iodine-131 of 1,250 times above the standard, it would be the equivalent of 1 millisievert, or the average dosage one is exposed to annually, according to the NISA.

One option after the crisis is resolved will be to encase the plant in a concrete casket as they did at Chernobyl.



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