(Corrects fourth paragraph of story published on Nov. 8 to show possible risks during removal of spent fuel.)
Tokyo Electric Power Co. plans this month to begin removing spent fuel from the wrecked Fukushima Dai-Ichi nuclear facility, the most significant test to date of its ability to contain the threat stemming from the worst nuclear disaster since Chernobyl.
An uncontrolled nuclear reaction due to structural failures or mishandled fuel is highly unlikely because of safeguards and workers’ experience with the procedure, Akira Ono, the Dai-Ichi plant’s chief supervisor, said at a news conference at the power station yesterday.
Ono’s remarks coincide with preparations to remove fuel rods from the No. 4 reactor’s cooling pool at the plant operated by Tepco, as the utility is known. The task is an early milestone in decommissioning that experts say could threaten another crisis if mishandled.
The No. 4 reactor building was heavily damaged by an explosion and fire in the days following the March 11 earthquake and tsunami in 2011. This led to concerns the nuclear rods in the spent fuel pool may have been damaged, adding to the risk of radiation release during removal, a process that will continue until the end of this year.
“I personally believe this kind of thing is very close to being impossible,” Ono said. “It’s not the first time for us to do this operation. At any ordinary nuclear power plant, workers remove spent fuel.”
Still, working amid high radiation emitted by other reactors with melted cores and dealing with possible debris remaining in the pool could present problems, Ono said.
The 1,533 fuel assemblies earmarked for removal are stored in a building heavily damaged by the March 2011 explosion. Removal is expected to begin this month, with practice drills scheduled for as early as next week, Ono said.
Some experts, such as former nuclear engineer Michael Friedlander, say Tepco could be playing down the dangers of the process.
“The thing that keeps me up late at night is that they’re getting ready to unload the spent fuel in unit 4,” said Friedlander, who spent 13 years operating U.S. nuclear plants
Tepco’s record of accidents at the plant, including power failures and contaminated water leaks, tests faith in its competence to perform such a delicate task, Friedlander said this week from Hong Kong during a phone interview. “It has the potential if it doesn’t go well to create a very, very serious accident,” he said.
Tepco plans to add 220 workers at the plant to contain contaminated water and to build higher barriers around storage tanks in a package of measures to improve management of the site, the company said in a statement today.
During a tour of the plant yesterday, crews in white Tyvek radiation-blocking overalls and respirator masks gathered around equipment in the fuel removal unit installed over the No. 4 reactor, making adjustments ahead of next week’s tests.
The fuel-removal unit is a large shoebox-shaped structure cantilevered atop the reactor building and held aloft by a grid of metal pillars. Inside, a technician will be seated on a gantry crane traversing the fuel pool, plucking out assemblies holding about 80 rods one-by-one with a telescoping hoist.
The fuel will be loaded into casks capable of holding as many as 22 assemblies. A separate, heavier gantry crane running close to the structure’s ceiling will lift the casks from an underwater loading area and lower them through a shaft leading to the ground below. Fuel will then be transported to a separate fuel-storage pool that suffered less damage during the quake.
Engineers have been examining the stability of the reactor building to make sure no new vulnerabilities have developed that could lead to accidents during removal. Quarterly tests have also been conducted to ensure the building isn’t sinking because of soil subsidence, Ono said.
Crews are scheduled to conduct their first tests of the removal system with actual fuel assemblies next week, Ono said. Technicians plan to lift and lower some of the assemblies sitting in the spent fuel pool.
While larger pieces of debris from the March 2011 explosion have been removed, any smaller bits remaining could “affect the smooth running of operation,” Ono said.
“In that sense, we are concerned,” he said, without giving details.
Fuel-removal technicians accustomed to operating in lower-radiation environments will have to wear masks and radiation-blocking clothing, which could make work more difficult, Ono said.
Ono said he’s confident that the operation at the No. 4 reactor, due to be finished by the end of 2014, will be completed without major problems.
“If there are people concerned about it, all we can do is explain that we can go ahead with the operation very safely,” he said. “I don’t think the operation itself is dangerous.”
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