Three of the spent fuel assemblies workers will pull out from the crippled Japanese nuclear plant at Fukushima suffered damage even before the 2011 earthquake and tsunami knocked out the facility.

The plant’s operator, Tokyo Electric Power Co., (Tepco), said they can’t remove the damaged assemblies, which are 4.5 meter high racks containing 50-70 thin rods of highly irradiated used fuel, from Fukushima’s Reactor No. 4 using the large cask assigned to taking out more than 1,500 of the assemblies.

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One of the assemblies suffered damage as far back as 1982, when workers mishandled it during a transfer, and it ended up bent out of shape, Tepco said in a brief note at the bottom of an 11-page information sheet in August.

In a statement from April 2010, Tepco said it found two other spent fuel racks in the reactor’s cooling pool had what appeared to be wire trapped in them. Rods in those assemblies have pin-hole cracks and are leaking low-level radioactive gases, Tepco spokesman Yoshikazu Nagai said Thursday.

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The existence of the damaged racks, reported in a Fukushima regional newspaper on Wednesday, came to light as Tepco prepares to begin decommissioning the plant by removing all the spent fuel assemblies from Reactor No. 4.

“The three fuel assemblies … cannot be transported by cask,” Tepco spokeswoman Mayumi Yoshida said Thursday, referring to the large steel chamber workers will use to shift the fuel assemblies from the pool high up in the damaged reactor building to safe storage.

“We are currently reviewing how to transport these fuel assemblies to the common spent fuel pool,” she said.

Tepco is due within days to begin removing 400 metric tons of the dangerous spent fuel in a hugely delicate and unprecedented operation fraught with risk. Each assembly contains radiation equivalent to around 10 times that of the atomic bomb dropped on Hiroshima in 1945.

Having to deal with the damaged assemblies is likely to make that task more difficult and could jeopardize a 12-month timeframe to complete the removal that many have already called ambitious.

Three reactors suffered core meltdowns at the Fukushima Daiichi plant north of Tokyo after the March 2011 disaster that triggered explosions and forced the evacuation of 160,000 people from nearby towns and villages.

Tepco, which has floundered in trying to bring the plant under control in the two and a half years since the disaster, is now moving to full decommissioning at the six-reactor facility.

The most urgent task is to remove the fuel assemblies from the unstable Reactor No. 4, which due to their height — about 18 meters above ground level — are more vulnerable to any new earthquake. The operation is a test of Tepco’s ability to move ahead with decommissioning the whole facility, which could take decades and cost tens of billions of dollars.

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