OSAKA, Japan — While Japan debates the possible restart of two nuclear reactors amid warnings of summer power shortages, the plant that prompted the shutdown of the country's entire nuclear industry is still a cause for concern.
Six months after the government declared that Fukushima Daiichi, where three reactors melted down following the earthquake and tsunami on March 11, 2011, had reached a stable state known as "cold shutdown," the focus has shifted to the condition of spent fuel rods being stored in a fourth reactor building.
Fukushima Daiichi's reactor No. 4, which was badly damaged by a hydrogen explosion last March 15, houses 1,535 uranium fuel assemblies and, some activists and politicians have warned, is vulnerable to collapse if the plant is rocked by a powerful earthquake.
A strong quake, they say, could also puncture the pool's casing and allow the water now being used to cool the fuel rods to seep away and cause a major release of radiation.
The minister in charge of the worst nuclear crisis in Japan's history, Goshi Hosono, recently took a small group of journalists inside the reactor to address concerns that the fuel storage pool, located on the fifth floor of the building, has the potential to cause a disaster even more serious than March 11, 2011.
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The reactor is particularly troublesome because it holds all of reactor No. 4's fuel rods — they had been removed to allow for maintenance work when the plant was hit by a 46-foot tsunami.
Hosono, however, said he accepted assurances by the plant's operator, Tokyo Electric Power (Tepco), that the unit would be safe in an earthquake similar in strength to the one that struck last March.
"A variety of concerns has been raised about the spent fuel pool at unit 4, and my goal was to assess the situation directly," Hosono said after a brief visit to the reactor dressed in protective clothing and flanked by security guards.
He said he had confirmed that the 33 foot by 66 foot (10 meter by 20 meter) pool had not tilted, adding that the surrounding structure had been reinforced with concrete and steel. Asked about a 3 cm outward "bulge" in one wall of the building, he said: "I have asked Tepco not to take an optimistic view, but to deal with it strictly in order to ... ensure safety. It is true that there are various issues left to deal with."
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Checks on the reactor building have revealed no major cracks or metal corrosion in the structure housing the pool, Tepco said. Even if the spent fuel rods were to be exposed after another earthquake, the utility added, it would take three weeks for them to gain sufficient heat to pose a threat. Preparations have been made to keep them cool with water or even to encase them in a special concrete-like mixture.
Tepco and the government moved to reassure the public after a US senator warned of massive radiation leaks in the event of a collapse or major damage to the fuel pool.
Ron Wyden, a Democratic senator from Oregon who recently toured Fukushima Daiichi, said authorities in Japan needed to move more quickly to put the fuel rods out of harm's way.
"The precarious status of the Fukushima Daiichi nuclear units and the risk presented by the enormous inventory of radioactive materials and spent fuel in the event of further earthquake threats should be of concern to all and a focus of greater international support and assistance," Wyden said in a letter to Japan's ambassador to the US, Ichiro Fujisaki.
The government acknowledged international concerns, but said the senator's warnings were misplaced.
"We have no evidence to support that the No. 4 reactor building is neither as sound or more dangerous structurally compared to the other buildings [on the Fukushima Daiichi site]," Ikko Nakatsuka, Japan's senior vice minister for reconstruction, told reporters.
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"But we understand that there are concerns about the reactor, including those that have been proven to be false. All we believe is that the situation of the facilities at the Fukushima plant is very different from other nuclear plants and thus stricter safety measures must be applied."
Reactor No. 4 is only one of four reactors at Fukushima Daiichi that will test Japan's ability to clean up the world's most hazardous industrial site. The government says it expects to begin removing the spent fuel rods from the storage pool in December 2013, but it will be another decade before workers can begin removing melted fuel from deep inside reactors Nos. 1-3.
Decommissioning the plant will take far longer. "This may take 30 or even 40 years to complete, and extremely difficult work is still ahead of us," Hosono said.