” OKUMA, Fukushima Prefecture–The 1,533 nuclear fuel assemblies were lined up in neat rows in the storage pool of the No. 4 reactor building amid new equipment and a clean environment.
But in stark contrast was the scene around the No. 4 reactor building at the Fukushima No. 1 nuclear power plant.
Concrete walls were still missing from the third and fourth floors of the No. 4 reactor building, raising questions among onlookers if the structure could withstand a huge earthquake.
On the sea side of the building, a piping system and metal rods were exposed behind collapsed walls of a former boiler building.
A truck swept up by the 2011 tsunami remained upside down by the side of the turbine building.
Amid these surroundings, Tokyo Electric Power Co. plans to start removing the nuclear fuel assemblies from the No. 4 storage pool as early as next week. The work would represent a new stage in the overall plan to end the nuclear crisis that started 32 months ago.
“It is a big step in the process to decommission the reactor,” Nuclear Regulation Authority Commissioner Toyoshi Fuketa said.
The entire decommissioning plan for the plant is expected to take 30 to 40 years to complete, and the strategy could change at any moment.
Workers still do not know the location of melted nuclear fuel in the No. 1, No. 2 and No. 3 reactors. High radiation levels are preventing entry to some areas. And contaminated water leaks continue to plague the site.
And removing the nuclear fuel from the No. 4 pool will require delicate procedures, considering the state of the building and the dangers involved.
NRA Chairman Shunichi Tanaka told TEPCO President Naomi Hirose to use extreme caution in removing the assemblies.
“The process involves a very large risk potential,” Tanaka told Hirose. “In a sense, it is more risky than the radioactive water crisis.”
TEPCO on Nov. 6 allowed reporters to see the spent fuel storage pool of the No. 4 reactor building and other areas of the stricken nuclear plant.
An elevator took the reporters to the top floor of the five-story building. A steel frame had been assembled near the pool, and a new fuel hoist and a new crane had been installed.
The No. 4 reactor building itself was covered by a canopy to replace the roof that was blown off in an explosion on March 15, 2011.
TEPCO plans to transfer the 1,533 nuclear fuel assemblies to a “storage pool for common use” 100 meters west of the No. 4 reactor.
The removal and transfer is expected to be completed at the end of next year.
The assemblies contain both spent and unused fuel. Some bundles were moved to the pool from the reactor core because the No. 4 reactor was undergoing a regular safety check when the Great East Japan Earthquake and tsunami struck the plant on March 11, 2011.
The disaster knocked out the cooling system for the storage pool, sparking fears that it would dry up, leaving the fuel exposed and allowing huge amounts of radioactive substances to spew into the air.
That didn’t happen. However, the explosion four days after the tsunami left large chunks of debris in the storage pool.
Those chunks have been cleared, but a number of smaller pieces remain in the storage pool.
The fuel removal process will use a cask receptacle that is 5.5 meters long, weighs 91 tons and can hold 22 fuel assemblies. It will be submerged in the pool and receive one fuel assembly at a time to prevent a nuclear reaction from occurring.
A crane will lower the receptacle to the ground, where a vehicle will pick it up and take it to the common-use storage pool.
TEPCO plans to use two receptacles to speed up the transfer process and finish removing all the fuel in just over a year.
In addition to uranium, spent nuclear fuel contains highly toxic plutonium and other radioactive substances, which could be released if the fuel assemblies are damaged during the removal or transfer process.
TEPCO has taken measures to check for deformed fuel assemblies and to prevent the remaining debris from causing damage when the fuel is pulled out.
The company has also decided to use double wires to ensure the receptacles are not dropped by mistake.
The canopy covering the No. 4 reactor building is designed to contain radioactive materials in the event of an accident. The bottom of the storage pool has also been strengthened with concrete and other materials.
The reinforced storage pool could withstand shaking as strong as the magnitude-9.0 Great East Japan Earthquake, TEPCO officials said. … ”