information about Fukushima published in English in Japanese media info publiée en anglais dans la presse japonaise
25 Août 2013
August 25, 2013
AP, AFP-JIJI, Kyodo
The huge radioactive water leak discovered at a storage tank last week at the Fukushima No. 1 nuclear plant was likely caused by deteriorating rubber seams and distortions that emerged after the tank was reassembled, Tokyo Electric Power Co. says.
Tepco said Saturday that the temporary tank, which held water used to cool the melted fuel in three of the plant’s shattered reactors, was moved and reassembled after it began sinking two years ago amid subsidence at the site.
On Aug. 19, Tepco revealed that 300 tons of the tainted water had vanished from the tank, marking the fifth and worst leak there since the March 2011 mega-quake and tsunami triggered the man-made disaster.
All five of the temporary tanks involved in the leaks were collapsible and held together by rubber seals, meaning they were less durable than those with welded seams.
Tepco spokesman Noriyuki Imaizumi said the tank passed a water-tightness test and other safety requirements after it was reassembled, but that the leak might have started when the seals began deteriorating, leading to contortions in the tank.
Tepco has not pinpointed the source of the leak but is concerned that moving and rebuilding it contributed to the incident, rated Level 3 on the International Nuclear Event Scale.
In all, three of the temporary tanks have had to be dismantled and moved because of sunken foundations, the beleaguered utility said. The tanks were relocated in September 2011.
The water in the other two, which are also at risk of leaking, was put in other tanks Sunday.
Nuclear regulators have raised concerns about the flaws of rubber-seam tanks and are urging Tepco to switch to welded-seam tanks, which take longer to assemble and are more expensive.
Tepco said it believes the water went directly into the ground, but that some might have flowed into the Pacific via a rain gutter.
About one-third of the plant’s nearly 1,000 storage tanks are of the rubber-seal type.
Nuclear regulators who toured the crippled plant after the leak was reported declared Friday that the handling of water storage at the site was “sloppy.”
More than two years since the crisis began, Tepco is stumbling badly on the cleanup while the water threatens to spark another environmental disaster.
Calls are growing for outside experts to step in and take control of the operation.
A tank that caused a serious leakage of radioactive water in the compound of the crippled Fukushima No. 1 nuclear power plant was transferred to its current location after causing the ground to subside where it was previously situated, Tokyo Electric Power Co., operator of the plant, said on Aug. 24.
TEPCO said the tank may have been damaged or distorted when the ground settled unevenly, which led to the leakage of about 300 tons of water highly contaminated with radioactive materials. The utility has acknowledged that the water may have reached the ocean, triggering a new crisis as it searches for the cause of the leak.
The 11-meter-high cylinder-shaped tank, with a diameter of 12 meters, has a storage capacity of 1,000 tons of water. It is made of steel plates connected with bolts, rather than being welded, which is considered a more sturdy construction method.
According to TEPCO, three tanks, including one that leaked the contaminated water, were initially installed at the previous location in June 2011.
The next month, workers poured water into the tanks to see whether they would leak. At that time, the ground subsided about 20 centimeters. Because of that occurrence, they dismantled the tanks.
Subsequently, the workers installed the tanks in the current location in October 2011. At that time, a subcontractor that checked the effects of the ground subsidence told TEPCO that there were no problems with them. They also poured water into the tanks at that time and confirmed that they were not leaking.
TEPCO plans to transfer highly contaminated water not only from the leaking tank, but also from the other two tanks on the site as a precautionary measure.
About 350 tanks of the same structure are currently being used in the compound of the nuclear plant to store water that was contaminated with radioactive materials.
“We are considering replacing them with new ones,” Zengo Aizawa, TEPCO executive vice president in charge of the nuclear power division, told reporters in the Fukushima prefectural government office in Fukushima on Aug. 24.
http://mainichi.jp/english/english/newsselect/news/20130825p2g00m0dm006000c.html
TOKYO (Kyodo) -- A huge storage tank from which about 300 tons of highly radioactive water leaked at the crisis-ridden Fukushima Daiichi nuclear power plant may have deteriorated and become deformed as a result of being moved and reassembled, plant operator said Saturday.
Tokyo Electric Power Co. said the tank was first installed at a different location in June 2011, after the Fukushima nuclear disaster was triggered by a huge earthquake and tsunami in March 2011.
But after its foundation was found to have cracked after the tank sank in the ground, it was dismantled and reassembled at its current location where the leak occurred, the utility said.
TEPCO is investigating whether partial damage or deterioration in the tank, whose foundation sank about 20 centimeters, had anything to do with the leakage.
The tank was one of three tanks that had to be dismantled and relocated because their foundations sank, the utility said. The tanks were relocated in September 2011.
The contaminated water in the two other tanks, which are also at risk of leaking, will be transferred to other tanks on Sunday.
TEPCO said workers, before reusing the tanks after reassembly, confirmed with their naked eyes that there were no leaks when they filled them with water.
On Monday TEPCO first noticed puddles with high radiation levels -- about 100 millisieverts per hour -- near where many storage tanks stand.
Some of the radioactive water might have flowed into the adjacent Pacific Ocean via drainage channels, data provided by TEPCO showed Wednesday. The same day, the Nuclear Regulation Authority said it is considering raising the severity assessment of the event to level 3 on an eight-point international scale from level 1.
Level 3 on the International Nuclear and Radiological Event Scale is defined as a "serious incident."
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