The first attempt to recover a tiny amount of highly radioactive fuel debris from Japan's crippled Fukushima Dai-ichi nuclear power plant was delayed shortly before the delicate maneuver was due to take place on August 22, but analysts and the operator of the plant insist the hold-up will be brief.

Although it had been hoped that the first debris could be retrieved as far back as 2021, experts say that ensuring safety remains the absolute priority and that delays are inevitable as nuclear engineers attempt something that has never been tried before.

"Retrieving fuel debris from the reactor buildings at the Fukushima plant is a very important task that can be said to be the core of decommissioning," an official of Tokyo Electric Power Co (Tepco) said in a statement to DW.

"Although the amount of debris retrieved in this trial retrieval will be only a few grams, we believe that there is a high possibility that analyzing as much information as possible from the retrieved fuel debris will greatly contribute to decommissioning work in the future," said the official, who declined to be named.

What does the clean-up entail?

Tepco officials emphasized that retrieving the debris "is an extremely difficult task that is unprecedented in the world. We will continue to proceed with the work carefully, with safety as our top priority, so as not to affect the surrounding environment."

On March 11, 2011, three of the facility's six reactors suffered meltdowns in the aftermath of a magnitude-9 earthquake that triggered a series of powerful tsunamis.

It was the worst nuclear disaster after the April 1986 crisis at Chernobyl. Radioactivity from the three damaged reactors spread across large parts of northeast Japan, where some areas remain off-limits to this day.

During the meltdown, nuclear fuel from the containment chamber melted and mixed with material that formed the jacket of fuel rods, along with debris inside the reactor building, before re-solidifying into debris.

Experts estimate that as much as 880 tons of debris, so highly radioactive that it would be fatal for a human to be near, remains in the three reactor buildings.

Experts selected the number 2 reactor for the initial test recovery. The plan called for a robotically operated device that resembles a telescoping fishing rod to be inserted through a hole in the side of the reactor.

A claw attached to the tip of the extending arm is designed to grasp a small chunk of debris, weighing as little as 3 grams, Tepco said.

Once recovered, the sample is to be transferred to a secure transportation box before being moved to facilities operated by the Japan Atomic Energy Agency to study the debris.

Why was the operation delayed?

The decision to delay the recovery maneuver was taken just hours before the planned start, when experts determined that the equipment had been wrongly assembled. Rectifying the problem should be straightforward, although Tepco was quickly the target of criticism.

An editorial published in the August 26 edition of the Mainichi newspaper expressed "disappointment at such a rudimentary error."

It added that it was "beyond comprehension just why the utility has made such a blunder," pointing out that had the operation gone ahead with the equipment incorrectly assembled, then there could have been "major trouble."

The Tepco official confirmed that it is investigating to determine how the mix-up occurred, but emphasized that the work to recover the debris will go ahead as there is no alternative.

"The risk associated with spent fuel has mostly been taken care of in the past few years by removing those fuels," said Vincent Gorgues, chief of staff to the French High Commission for Nuclear Energy and presently one of three international advisors to Japan's National Damage Compensation and Decommissioning Corp.

"The main remaining safety risk source is the presence of fuel debris at the bottom of the three different units," he told DW. "As soon as the fuel debris can be retrieved and stored – even if that is temporary safe storage – then the remaining hazard potential will have decreased by several orders of magnitude," he added.

The knowledge gained and the techniques honed in the recovery effort at the number 2 reactor will be "very helpful" for the subsequent retrieval of debris from the other two reactors, Gorgues said.

Progress varies between reactors

Work at the number 2 reactor is the most advanced, in part because the building did not experience a hydrogen explosion in the immediate aftermath of the earthquake.

At number 3, engineers are working on ways to "define and implement the best methodology to access and retrieve the fuel debris," Gorgues said. Work is still under way at the number 1 reactor to gather information to get a fuller picture of the situation inside the building.

Gorgues also defended Tepco from some of the criticisms that it has received.

"I want to emphasize that the teams are set to encounter difficulties, setbacks and technical problems. This is perfectly normal. This is not a walk in a park and there will be additional problems," he said.

"The main thing is the ability of the teams, project management, engineering and research and development, to work together and overcome these difficulties. They have done it successfully in the past few years and I trust them to do it again and again, for as long as it takes," he added.

The Tepco official added that the delay in the retrieval work will not impact the timeline for the complete decommissioning of the entire site, which is presently estimated to take between 30 and 40 years.

Edited by: Wesley Rahn