Concern is mounting as Tepco, operator of Japan's crippled Fukushima Plant prepares for what may be the most dangerous phase yet in the decommissioning process.

The work, to begin removal of 1,300 spent fuel assemblies from the remains of the reactor No 4 building, is scheduled for mid-November. The rods were being stored in a pool 100 feet above ground when the plant was struck by a tsunami March 11, 2011.

The head of Japan's Nuclear Regulation Authority, Shunichi Tanaka, warned the planned operation would be more hazardous than usual because the storage pool is filled with debris as a result of hydrogen explosions that occurred during the disaster.

"It's a totally different operation than removing normal fuel rods from a spent fuel pool," Tanaka was quoted as saying by The Guardian newspaper Thursday. "They need to be handled extremely carefully and closely monitored. You should never rush or force them out, or they may break. I'm much more worried about this than I am about contaminated water."

Tepco will use a remote-controlled crane installed inside the reinforced reactor building to remove, one by one, the fuel assemblies, which will be placed in dry casks before being moved to a common cooling pool in an adjacent building.

In a video released this week explaining its plan to remove the rods, Tepco said, "This transfer from one form of underwater storage to another will not lead to any radiation exposure to workers or anyone else."

But Charles Perrow, a Yale University professor who analyzes high-risk technologies, told the Australian Broadcasting Corp. one pool contains 10 times as much radioactive caesium-137 as was released at Chernobyl and warned that one mishap with the removal of the highly radioactive fuel could trigger a chain reaction.

"Tokyo would have to be evacuated because of caesium and other poisons that are there will spread very rapidly," Perrow said, referring to the consequences of such a mishap. "Even if the wind is blowing in the other way it's going to be monumental.

"This has me very scared," Perrow said.

Tepco has long been under fire for its handling of the disaster, and the plant has been plagued by a series of problems.

Six workers at the plant were accidentally doused in radioactive water this month. The week before that, Tepco said there was a radioactive water leak after workers overfilled a storage tank. In August the company said 300 tons of radioactive water had leaked from a storage tank into the ground. In July, Tepco admitted radioactive water was going into the sea.

While Tepco hopes to complete the removal of the 1,300 spent fuel assemblies before the end of next year, the entire process of decommissioning the plant is expected to last around 30 years and cost more than $1 billion, The Guardian reported.