The operator of the crippled Fukushima Daiichi nuclear power plant is planning to conduct robotic probes and collect samples from damaged reactors this year.
The work will be a key step in the effort to decommission the plant.
The No.1, 2 and 3 reactors suffered meltdowns following a major earthquake and tsunami in 2011.
Nuclear fuel melted and collapsed into the reactors' containment vessels. It mixed with surrounding metal parts and formed solid fuel debris.
Tokyo Electric Power Company plans to begin a robotic survey of the No.1 reactor in mid-January. The survey is expected to take about six months.
The robots will use ultrasonic devices to locate and measure the thickness of the deposits.
Utility officials say they also hope to collect samples.
Preparation to retrieve fuel debris from the No.2 reactor is underway with a robotic device that was developed in the UK.
It is now undergoing performance tests in Japan.
Tokyo Electric Power Company is planning to collect a few grams of debris with the robot by the end of this year. It hopes to gradually increase the amount to be retrieved.
Removal and safe storage of the extremely radioactive debris is thought to be one of the biggest challenges in the decommissioning process.