Unchartered territory

November 19, 2013 

TEPCO takes on long, unprecedented mission in decommissioning nuke reactors

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201311190056

THE ASAHI SHIMBUN

Workers at the Fukushima No. 1 nuclear power plant are in uncharted territory, facing the risk of damaging fuel rods and scattering radioactive materials during a yearlong mission to remove fuel from a storage pool strewn with debris.

On Nov. 18, Tokyo Electric Power Co., the plant operator, began removing fuel from the pool in the No. 4 reactor building, whose roof and walls were blown off in a hydrogen explosion in the early stages of the nuclear crisis set off by the 2011 earthquake and tsunami.

“We are confident (we can carry it through), but we will proceed with caution,” Noriyuki Imaizumi, acting general manager of TEPCO’s Nuclear Power and Plant Siting Division, said of the work under way at the No. 4 reactor building.

Under normal operating procedures, fuel-handling equipment automatically moves to the locations of fuel to be removed.

But in this case, workers have to visually check the locations because fuel units are not necessarily in their regular positions due to the hydrogen explosion.

Large pieces of rubble generated by the explosion have been cleared, but small fragments still remain in the water-filled pool.

On Nov. 18, workers using special equipment moved four fuel assemblies to a cask, a cylindrical container used for transportation, one at a time. Work was monitored through underwater cameras.

Workers spent about 40 minutes to transfer each fuel assembly to the cask, slowly moving each unit about one centimeter per second.

After 22 fuel assemblies are in the cask, it will be transported to a common storage pool about 100 meters away. TEPCO said it will take until December 2014 to move all 1,533 fuel assemblies.

Six teams, each made up of six workers, will take turns doing the fuel removal work. Each team will work for up to two hours due to high radiation levels.

If nuclear fuel is damaged, radioactive materials could be released. Equipment will automatically stop when abnormal conditions are detected.

Radioactive materials could also escape if a cask is broken, for example, if a powerful quake hits while operations are in progress.

TEPCO said such an accident is unlikely due to the precautions it has taken, including the use of duplex cask-hoisting wires.

In addition, parts of the building under the pool have been reinforced with steel frames and concrete to improve quake resistance. Steel shielding has also been installed over the building.

Officials estimate that potential effects outside the plant premises would be limited in the event a cask breaks.

But workers would have to evacuate, depending on radioactivity levels. If work is suspended for an extended period, the decommissioning schedule will have to be reviewed.

“More than a few employees have expressed concern that the work may not proceed smoothly,” said a senior official of Tokyo Power Technology Ltd., TEPCO’s wholly owned subsidiary responsible for fuel removal.

The company used to change fuel at the plant before it was damaged by the Great East Japan Earthquake and tsunami. But until now, no one has experience in removing fuel from a debris-scattered pool.

Workers will have to wear three layers of gloves, made of cloth or vinyl, and a mask to protect against high radiation levels while carrying out their tasks. Workers complained that finger grips feel different from when they are without gloves and that it is difficult to breathe through a mask.

A man who has been working at the plant since before the disaster said he does not feel anything special about the current decommissioning work.

“Before the accident, it was a big deal if we dropped a pen in a storage pool,” said the man, who now inspects radioactive water storage tanks and does other jobs. “Today, I do not feel the same way, although small debris fragments remain in the pool. I think my senses have become numb due to the extraordinary situation that has continued since the accident.”

High radioactivity levels have prevented workers from entering areas of the No. 1 to No. 3 reactors, which went into meltdown in the early stages of the disaster. Removal of spent nuclear fuel in those three reactor buildings is expected to begin in 2015, at the earliest.

TEPCO hopes to start removing the melted fuel from the No. 1 to No. 3 reactors in fiscal 2020.

Overall decommissioning work at the plant is expected to take 30 to 40 years.