Mountains of rubble stand in the way of decommissioning the No. 4 reactor of the Fukushima No. 1 nuclear power plant, part of an unprecedented challenge facing Japan to decommission four crippled reactors.
The No. 4 reactor building was opened to a handful of media organizations on May 26 for the first time since the nuclear crisis was triggered following last year's March 11 Great East Japan Earthquake and tsunami.
A reporter from the Tokyo Shimbun described the scene on the fourth floor as looking like that of a "battlefield after being bombed." The wall facing the sea had been blown off in a hydrogen explosion on March 15 last year.
"Pipes were severely bent," the reporter said. "Steel frames were also twisted and rusted. It was hard for me to believe such a thick wall was blown off over a wide area."
A tour of the No. 4 building by media outlets was given to coincide with an inspection by Goshi Hosono, minister in charge of handling the nuclear disaster.
What is most under threat in the No. 4 building, experts in and out of Japan say, is the spent fuel pool, which holds 1,535 fuel assemblies, an equivalent of those in three reactors.
Many point out the risks of the collapse of the pool if another huge temblor with the power of last year's quake strikes the plant.
To dismiss concerns about potential risks to the No. 4 building, TEPCO released a report on May 25 stating that the structure had an outward bulge of 3.3 centimeters in a portion of its west wall due to the hydrogen explosion, but did not pose a threat to its structural integrity.
Hosono said after the tour that the government accepted Tokyo Electric Power Co.'s assurance of the safety of the building.
“The government has concluded that even if an earthquake measuring ‘upper 6’ (on the Japanese scale of 7) hits, the No. 4 building will be able to withstand the impact,” Hosono said. “The wall buckling out is situated away from the pool, but the government has ordered TEPCO to double-check the safety of the building as we take the situation seriously.”
TEPCO reinforced the structure of the pool by adding steel support and concrete beneath the pool in July.
The utility also said that it would take two or three weeks for spent fuel rods to start being exposed in the event of the pool's cooling system being knocked out.
On the fifth floor of the No. 4 reactor building, the top floor, the Tokyo Shimbun reporter could see the upper part of the spent fuel rod pool, which was covered with a floating white tarp.
"I could catch a glimpse into the water surface of the pool, but the water looked too stagnant to see the fuel rods seven meters beneath," he said.
The reporter said he was not entirely reassured by the utility’s promise that the structure will be sturdy enough to remain unscathed in another big quake despite no major, visible damage to the wall near the pool.
"TEPCO said that the pool can withstand a temblor equivalent to the quake last year, but I was not convinced of that," the reporter said.
The decommissioning work is said to be farthest along in the No. 4 building, compared with the buildings housing the No. 1 through No. 3 reactors, where three meltdowns occurred.
The No. 4 reactor was offline when the quake and tsunami struck. TEPCO plans to start moving the fuel rods from the No. 4 reactor spent fuel pool to a nearby common pool in December 2013 and complete the work in about two years.
To proceed to that stage, debris left on the upper floors of the building after the hydrogen explosion must be cleared.
But TEPCO said only 60 percent of the work has been completed since the process began last autumn. An excavator has been brought in on the fifth floor of the No. 4 reactor building to remove debris.
The decommissioning of the four reactors is expected to take at least 30 years, according to the mid- to long-term road map released in December by the government and TEPCO.
It will take 20 to 25 years to finish retrieving all the melted fuel left in the three reactors.
TEPCO is now preparing for decontamination work at the No. 1 through No. 3 reactor buildings to pave the way for workers to begin the retrieval of melted fuel rods.
The utility plans to remove debris and damaged walls at the No. 4 reactor building by autumn this year, a required step before it begins removing spent fuel rods in the pool.
It envisages covering the No. 4 building with a canopy by next summer to reduce the release of radioactive materials into the atmosphere.
A crane and other equipment needed to move the fuel rods will be installed in autumn 2013 so that technicians can start the retrieval process.
But there are many uncertainties that could easily derail TEPCO’s timetable, experts say.
The plan could be delayed because clearing the structure could take more time than expected because concrete blocks and pieces of steel frame are scattered all around in and out of the No. 4 reactor pool.
TEPCO also needs to secure a facility to store fuel rods from the pool, as a common nearby pool has space for only 465 fuel rods remaining.
The No. 1 through No. 3 reactors are being cooled by makeshift cooling systems, resulting in the leakage of a large amount of highly contaminated water at the plant.
High levels of radiation in the drainage are preventing the utility from preparing for the start of decommissioning work.
TEPCO will also have to proceed with decommissioning amid concerns for possible powerful aftershocks and tsunami.
It said that the reactors will be cooled with emergency cooling pumps even if the existing cooling systems are knocked out in such an event.
If a tsunami strikes the plant when the decommissioning work is under way, the makeshift cooling systems could be destroyed and contaminated water could leak into the sea.
TEPCO said the plant will be shielded from tsunami up to 8 meters high, as it erected a temporary breakwater up to 14 meters from the sea surface on a stretch of about 380 meters along the sea as a safeguard.
But the ability of the breakwater to withstand a tsunami 13 meters high, just like the one last year, is being questioned since it was built using buckets of stones piled atop each other.
The utility needs to put up a full-fledged breakwater in the future, but has yet to draw up a specific plan for one.
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