19 march 2013

Fukushima nuclear plant loses power

By Jonathan Soble in Tokyo, Financial Times March 19, 2013

A power failure at Japan’s Fukushima Daiichi nuclear station which shut down critical cooling systems for more than a day, has highlighted lingering hazards at the crippled facility, two years after it was devastated by the tsunami.

The widespread loss of power, which began on Monday night, was the most serious systems failure at the plant since it was restored to a state of relatively safe “cold shutdown” in December 2011, nine months after the accident. Power was fully restored by late on Tuesday night.

Tokyo Electric Power, the plant’s owner, said there was no immediate danger because the pools had been cooled to well below safe levels since the accident at the plant in March 2011.

Still, the breakdown of such a critical system is a reminder that the situation at remains fraught even after a two-year repair effort. Full disposal of dangerous materials inside the plant will take years, during which time the badly damaged facility will remain vulnerable to potential new accidents.

Last year, Tepco reinforced the floor of the most crowded and damaged storage pool, in reactor number 4, with steel columns and cement. It had been put on the defensive about the potential danger posed by the pool by Ron Wyden, a US senator, who declared the situation “precarious” after a visit to the plant.

He said he feared a loss of containment that would result in an “even greater release of radiation than the initial accident”.

The subsequent discovery that one wall of the Unit 4 building has buckled outward by 3cm, a result of explosions or the earthquake or both, added to concerns.

The power failure appeared to have been caused by a problem with temporary electrical distribution boards installed by emergency workers, Tepco said. It affected nine separate areas of the plant, including the plant’s earthquake-proofed control building, newly built since the facility’s battering by the tsunami; a system for purifying coolant water; three of four fuel storage pools located inside the damaged reactor buildings; and a larger secondary storage pool on the site, which was the last still to be restored on Tuesday.

Tepco said water supply to the three reactor cores that melted during the accident was not interrupted.

Power in the control building was restored relatively quickly on Monday night, but engineers appeared to struggle with other areas. Thousands of tonnes of water is constantly cycled through the reactors and spent-fuel pools to keep the uranium inside from overheating and releasing radiation.

Together, the pools that lost power contain about 9,000 uranium fuel rods that had been removed from the reactor cores before the accident.

Temperatures inside the pools were between 15 and 30 degrees Celsius at 10am Japan time on Tuesday, Tepco said. The utility estimated that the pool in reactor number 4 would reach 65 degrees – the upper end of the threshold that regulators regard as safe – in four and a half days. The other pools are likely to take between seven and 27 days.

During the accident, water reached boiling point and evaporated, leaving fuel rods exposed to the air and releasing explosive gasses and radioactive particles.

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