Operator Tokyo Electric Power (TEPCO) said it had begun the process of removing the uranium and plutonium rods from a storage pool -- a tricky but essential step in the complex's decades-long decommissioning plan.
The operation follows months of setbacks and glitches that have stoked widespread criticism of the utility's handling of the crisis, the worst nuclear accident in a generation.
The work pales in comparison with the much more complex task that awaits engineers, who will have to remove the misshapen cores of three other reactors that went into meltdown before being brought under control two years ago.
Over the course of two days, the company said it expects to remove 22 assemblies, with the entire operation scheduled to run for more than a year.
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"At 15:18 (0618 GMT), we started to pull up the first fuel assembly with a crane," a company spokesman said today.
The huge crane, with a remote-controlled grabber, is being lowered into the pool and then hooked onto the assemblies, placing them inside a fully immersed cask.
Experts have warned that slip-ups could trigger a rapid deterioration in the situation. Even minor mishaps will create considerable delays in the already long and complicated decommissioning.
While such operations are routine at other nuclear plants, the disaster has made conditions far more complex, TEPCO has said.
"This is an important process that is an inevitable part of the decommissioning process, but it includes work that could pose a great risk," the Citizen's Nuclear Information Center, an independent energy think tank, said in a statement.
Hiroaki Koide, assistant professor at Kyoto University's Research Reactor Institute, said the timing of the fuel rod removal was crucial as "the reactor's storage pool is in an unstable condition".
Koide added that the whole decommissioning process would involve tasks that pose "unprecedented challenges".