TOKYO -- An attempt to use a telescoping robot to remove a sample of melted fuel from a wrecked reactor at Japan’s tsunami-hit Fukushima Daiichi nuclear power plant was suspended Thursday due to a technical issue.

The retrieval of a small sample of the debris within the Unit 2 reactor’s primary containment vessel would mark the beginning of the fuel debris removal process, the most demanding phase in the decades-long decommissioning of the plant where three reactors were destroyed in the March 11, 2011, magnitude 9.0 earthquake and tsunami disaster.

The operation was stopped on Thursday morning when workers discovered that five 1.5-meter (5-foot) pipes used to move the robot were incorrectly assembled and could not be fixed within the allotted time for their radiation exposure, according to the plant operator Tokyo Electric Power Company Holdings.

The pipes were intended to guide the robot into the reactor and then withdraw it once the task was completed. The robot is controlled remotely from a secure location once it is inside the vessel.

The robot can extend up to 22 meters (72 feet) to reach its target area and collect a fragment from the surface of the melted fuel mound. It utilizes a device equipped with tongs that are attached to the robot's tip.

The mission to retrieve and return the fragment is anticipated to span two weeks. TEPCO has yet to announce a revised start date.

The sample-return mission marks a crucial initial step in the decades-long decommissioning effort at the Fukushima Daiichi plant. However, the mission's objective of retrieving less than 3 grams (0.1 ounce) from an estimated 880 tons of highly radioactive molten fuel highlights the immense challenges involved.

While the retrieved debris sample is small, experts emphasize its value in providing crucial data for the development of future decommissioning methods, technologies, and robots.

A thorough understanding of the melted fuel debris is paramount to the successful decommissioning of the three damaged reactors and the entire facility.

Despite criticism of the timeline's feasibility, the government and TEPCO are committed to their initial 30-40 year cleanup goal set shortly after the meltdown. Comprehensive strategies for the complete removal and storage of the melted fuel debris remain undefined.