Some spent fuel rods at Fukushima were damaged before 2011 disaster

Mr Lake Barrett (right), a member of Tokyo Electric Power Co's (Tepco's) outside reform committee and independent consultant in the energy field, inspecting the No.4 reactor building at Tepco's Fukushima Daiichi nuclear power plant in Fukushima prefe
Mr Lake Barrett (right), a member of Tokyo Electric Power Co's (Tepco's) outside reform committee and independent consultant in the energy field, inspecting the No.4 reactor building at Tepco's Fukushima Daiichi nuclear power plant in Fukushima prefecture on November 13, 2013, in this handout photograph taken and released by TEPCO. -- FILE PHOTO: REUTERS

TOKYO (REUTERS) - Three of the spent fuel assemblies due to be carefully plucked from the crippled Japanese nuclear plant at Fukushima in a hazardous year-long operation were damaged, even before the 2011 earthquake and tsunami that knocked out the facility.

The plant's operator, Tokyo Electric Power, or Tepco, said the damaged assemblies - 4.5 metre high racks containing 50-70 thin rods of highly irradiated used fuel - could not be removed from Fukushima's Reactor No. 4 using the large cask assigned to taking out more than 1,500 of the assemblies.

One of the assemblies was damaged as far back as 1982, when it was mishandled during a transfer, and is 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 told Reuters on Thursday.

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 spokesman Mayumi Yoshida said in an emailed response to queries on Thursday, referring to the large steel chamber that will be used 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 tonnes 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 jeopardise a 12-month timeframe to complete the removal that many have already called ambitious.