It will take six months to a year to analyze a tiny sample of radioactive debris retrieved by a robot from Tokyo Electric Power Company Holdings' crippled Fukushima No. 1 nuclear plant, its operator said Thursday.

The analysis could shed light on radioactivity levels and the chemical structure of the fuel debris — a key part of preparation for the decadeslong decommissioning process.

Around 880 tons of hazardous material remain at the Fukushima plant, more than 13 years after a tsunami caused by an earthquake triggered one of the world's worst nuclear incidents.

Last week, the sample, weighing just below 0.7 gram — equivalent to about one raisin — was delivered to a research lab near Tokyo for analysis.

It had been removed from a reactor by an extendible robotic device in a tricky operation suspended several times by technical problems.

"Six months to a year will probably be needed" to fully probe the material, Akira Ono, chief decommissioning officer of plant operator Tepco, told a briefing.

"We're confident we can obtain data that will further enlighten us on how the fuel debris was formed in the first place, and what we need to be aware of when removing such debris on a large scale in the future," Ono added.

Although the size of the sample is "extremely small ... there is a lot of information that can be gleaned from it, given how advanced the analysis technology is today," he said.

Three of the Fukushima No.1 plant's six reactors went into meltdown in 2011 after the huge tsunami swamped the facility.

Last year, Japan began releasing into the Pacific Ocean some of the 540 Olympic swimming pools' worth of reactor cooling water amassed since the disaster.