TEPCO prepares to remove nuclear fuel at Fukushima plant 東電は、燃料棒の取り出しの準備に

November 07, 2013
By TOSHIO KAWADA/ Staff Writer
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.

MYSTERIES REMAIN AT NO. 1 TO NO. 3 REACTORS
The government and TEPCO announced the three-stage road map for decommissioning the Fukushima reactors in December 2011.
The first stage involves preparatory work, such as clearing debris, followed by the second-stage program that includes the removal of nuclear fuel from the pool in the No. 4 reactor building.


According to the road map, work to remove spent nuclear fuel from the pool in the No. 3 reactor building should start in the first half of fiscal 2015. But high radiation levels have prevented workers from approaching the No. 3 reactor, meaning that remote-control equipment will be needed to assess the situation.
The road map does not specify when the removal work will be completed there.
Removing the melted nuclear fuel from the No. 1 to No. 3 reactors is part of the third stage, and it is expected to start in fiscal 2020 at the earliest.
Engineers will first study methods to deal with the melted fuel, followed by the installation of equipment for the task. Currently, remote-control robots are being developed to study the situation and reduce workers’ exposure to radiation.
The locations and the condition of the melted fuel for these reactors remain a mystery. It apparently dropped to the containment vessels through the inner pressure vessels housing the reactor cores.
In addition, TEPCO has not determined the extent of damage to the pressure and containment vessels.
TEPCO plans to insert a small remote-control device equipped with a camera into the suppression pool in the bottom part of the containment vessel of the No. 1 reactor on Nov. 13 at the earliest to get an idea of the internal situation.

The road map for decommissioning work could drastically change depending on the conditions of the melted nuclear fuel and the damage to the containment vessels.

ONGOING CONTAMINATED WATER PROBLEM
One obstacle in the decommissioning plan is the continuous leaks of water contaminated with radioactive materials.
The Alps system that can remove 62 types of radioactive materials, including strontium, from water is scheduled to be put into full operation within this month.
It is considered a key piece of equipment to cut down the workers’ risk of exposure to radiation.
On Nov. 6, the Alps system was still not operational.
Under a tent the size of a gymnasium, where the Alps equipment is stored, workers were inspecting tanks and piping while using cranes hanging from ceilings to relocate containers.
Test runs of Alps started in March. But the operations were suspended in June after water was found leaking from some of the tanks in the system.
On Sept. 27, Alps operations were restarted, only to be shut down the same day due to a different problem.
Contaminated water is increasing by about 400 tons every day at the plant due to the continuing cooling of the reactors and groundwater entering cracks in the buildings and mixing with radioactive water.

TEPCO has removed only cesium from about 380,000 tons of contaminated water so far. And since even the Alps system cannot remove tritium, TEPCO has no choice but to store the radioactive water at the site.
In April, radioactive water was found to have leaked from an underground storage tank. In August, 300 tons of highly contaminated water had spilled from a tank and likely reached the ocean.
Other leaks have also taken place, spreading soil contamination in the plant’s compound.
Workers on Nov. 6 were seen heightening barriers and embankments to prevent radioactive water from spilling over the encasements surrounding tanks holding contaminated water.
About 200 workers have been assigned to monitor the tanks for possible leaks.
“The division to deal with contaminated water is different from the one to remove nuclear fuel. So we will be able to sufficiently carry out work for the two issues,” said Akira Ono, director of the Fukushima No. 1 nuclear power plant.
However, TEPCO Vice President Zengo Aizawa was not so optimistic.
“From the mid- and long-term perspective, I have concerns,” Aizawa said.