By Aaron Sheldrick
TOKYO (Reuters) - The operator of Japan's wrecked Fukushima atomic plant removed 400 tonnes of spent uranium fuel from a damaged reactor building, the first of four sets of used rods to be removed in a cleanup expected to last decades.
The year-long operation is a rare success for Tokyo Electric Power Co since the meltdowns at the Fukushima Daiichi nuclear plant north of Tokyo more than three years ago. The overall clean-up has been plagued with delays and leaks of radioactive water.
The utility known as Tepco completed the removal of 1,331 spent fuel rods from the upper levels of the badly damaged reactor No. 4 building on Wednesday, a spokeswoman said.
The No. 4 building was a source of concern during the disaster because of fears it would collapse in another earthquake, leading to exposure of the spent fuel.
Tepco still needs to remove 180 fuel assemblies that haven't been used but these are considered less dangerous than spent fuel as they have not been irradiated in the reactor.
The unused assemblies will be moved to reactor No. 6, which was unscathed when an earthquake and tsunami knocked out power and cooling in March 2011 causing the worst nuclear disaster since Chernobyl in 1986.
The spent rods and 22 unused assemblies were placed in a storage pool at ground level at the plant, Tepco said.
It must repeat the task in the three reactors that experienced meltdowns during the disaster and are holding almost 1,400 fuel assemblies in storage pools on their upper floors.
Once the spent fuel has been removed, Tepco can address the most difficult task of extracting the three reactor cores that melted during the crisis, an unprecedented occurrence.
Tepco and the Japanese government plan to delay by five years the removal of the melted fuel to around 2025 because of holdups in the decommissioning work, Kyodo News reported last week.
(Reporting by Aaron Sheldrick; Editing by Nick Macfie)