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Tuesday, Dec. 6, 2011

Fukushima plant springs new water leak

Strontium spike feared; sandbags used to halt flow

Staff writer

Some 45 tons of highly radioactive water leaked Sunday from desalination equipment used to decontaminate the radioactive water in Tokyo Electric Power Co.'s Fukushima No. 1 nuclear plant and it is unclear if any made it to the sea, a Tepco official said Monday.

The water is believed to have high concentrations of strontium, which can cause bone cancer if ingested. The decontamination system Tepco is using to stablize the crippled reactors mainly removes cesium, but does little to mitigate strontium.

It is not known if some of the leaked water reached the sea, the water table or flowed off the plant's premises. Tepco used sandbags Sunday to contain the water, 300 liters of which escaped from a concrete machine building through a crack, Tepco spokesman Hiroki Kawamata said. The machine building, which houses the decontamination equipment, is on the landward side of the reactors.

"Even if all 300 liters reached the sea, the radiation would be diluted, and the amount that escaped is tiny compared with what has already leaked into the sea (on earlier occasions)," said Genichiro Wakabayashi, a radiology professor at Kinki University, playing down the potential danger of the leak. "The leak (even if to the sea or to the groundwater) would not be enough to increase radiation levels in marine or agricultural products in the Tohoku region," he said.

Beta ray radiation of 110 millisieverts per hour was detected in the air over in a gutter outside the building where the water pooled, along with gamma ray radiation of 1.8 millisieverts per hour, Tepco said. Beta rays do not travel far and are easily stopped by thin material, including clothing. Gamma rays, however, are much more powerful. Strontium mainly emits beta rays, while cesium emits gamma rays.

The numbers compare with about 2.0 microsieverts of hourly atmospheric radiation in Iitate, Fukushima Prefecture, where residents were ordered to evacuate.

The utility is testing seawater samples taken off the coast near the plant to see if it is contaminated with strontium. It will know the results in about two to three weeks, Tepco said.

The machine building houses one of the two sets of desalination systems. In the early stages of the meltdown crisis, Tepco used seawater to cool the overheated reactors for a couple of weeks because coolant water stopped circulating when the March 11 tsunami knocked out the power generators.

The system that suffered the leak had been shut down. Operations resumed around 2:30 p.m. Saturday and the leak was detected at around 11:30 a.m. Sunday, Kawamata said.

A worker found the leak spewing from the desalination apparatus and out of a crack in the wall of the building, prompting Tepco to quickly switch off the machine, he said. The leaked water probably flowed through the gutter outside the wall because air above a concrete lid on the gutter had an unusually high radiation reading, he added.

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The Japan Times

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