Workers have begun the delicate task of removing fuel rods from a storage pool at the Fukushima Daiichi nuclear power plant, more than two and a half years after the facility suffered a triple meltdown after being hit by a powerful earthquake and tsunami.

The operation to remove more than 1,331 used fuel assemblies and 202 unused assemblies began on Monday and is expected to take just over a year. Decommissioning the entire site is expected to take at least 30 years.

The plant's operator, Tokyo Electric Power [Tepco], said the fuel removal was an important step in decommissioning the plant, which experienced multiple meltdowns and explosions after Japan's north-east coast was hit by a powerful earthquake and tsunami in March 2011.

Tepco brushed off fears that removing the rods from near the roof of reactor No 4 could cause a serious accident. Some experts have warned that a collision involving the fuel assemblies, a sudden loss of coolant water or another earthquake could cause a chain reaction and release huge quantities of radiation into the atmosphere.

Reactor No4 was closed for routine maintenance at the time of the disaster and so did not suffer a meltdown. But a hydrogen explosion on 15 March 2011 blew the walls and roof off the reactor building, leaving it vulnerable to further damage from earthquakes.

The utility has since reinforced the building with a huge steel canopy and insists the structure can withstand seismic events of the same intensity that shook the plant in March 2011.

But it conceded that the fuel assemblies needed to be moved to a safer storage site as soon as possible.

"After the explosion, one big challenge was to deal with the spent fuel pool, because if the water evaporated it would cause a radioactive cloud stretching all the way to Tokyo, which would have to be evacuated," Yuichi Okamura, deputy manager of the water treatment department at Fukushima Daiichi, told the Guardian on Monday.

"It was a big challenge, so today is a big success for the cleanup teams."

Yoshimi Hitosugi, a Tepco spokesman, said: "This is an important moment. It is one big step towards decommissioning the reactor." He added that three fuel assemblies had been discovered that were damaged prior to the tsunami and measures were being taken to deal with them.

Hitosugi said the firm was confident that the workers would be able to cope with any debris caused by the explosion that remained in the spent fuel pool, adding that it would not compromise the fuel removal operation.

Tepco's president, Naomi Hirose, said the fuel extraction "represents the beginning of a new and important chapter in our work", and thanked plant workers for the "ingenuity, diligence, and courage that made this achievement possible".

The utility believes that a specially chosen team of 36 men will need until late 2014 to remove all of the fuel assemblies from the pool, located 130 feet above ground, and place them in submerged protective casks. The casks will then be taken to ground level and transported to a more stable storage pool nearby.

Each cask can hold up 22 assemblies comprising between 60 and 80 fuel rods. Workers will remove the fresh fuel assemblies first because they are easier to handle.

"The extraction work started at 3:18pm and the first fuel completed its extraction from the fuel rack to the cask placed inside the pool at 3:57pm as planned, following thorough safety preparations with the co-operation of many partner companies and individual workers," Tepco said in a statement.

But antinuclear campaigners have voiced concern over Tepco's ability to complete the work without incident following revelations that up to 300 tonnes of radioactive water are leaking from the site into the sea every day.

The utility also came under fire this summer for installing poorly designed tanks that leaked toxic water.

"We are concerned that Tepco may not be capable of conducting this risky operation safely, and that there are significant risks involved in this operation," said Kazue Suzuki, a nuclear campaigner with Greenpeace Japan.

"Tepco's inability to solve the problems with leaking tanks that store contaminated water, and the continued flow of contaminated water from the site to the ocean adds to our concerns about its ability to handle this dangerous operation to remove spent fuel.

"If Tepco makes mistakes again and can't handle this task, workers could be exposed to excessive levels of radiation and in a worst-case scenario there could be a massive new release of radiation to the atmosphere."

The head of Japan's nuclear safety agency, Shunichi Tanaka, recently warned that removing the fuel involved huge risks, particularly if any attempt were made to force fuel assemblies that have become impeded by debris. "The process involves a very large risk potential," he said. "In a sense, it is more risky than the radioactive water crisis."

According to Tepco, the specially designed handling equipment has inbuilt mechanisms to prevent the fuel from being accidentally dropped, and that even breakages in a small number of fuel assemblies would not pose a risk to areas around the plant.

Local authorities in Fukushima will send emergency notifications to residents via mobile phones and other devices in the event of an accident.

Even if the fuel removal ends without a hitch, Tepco faces the even more difficult task of locating and removing melted fuel from deep inside the three reactors that suffered meltdown.

Radiation levels inside those reactors are still too high for humans to enter, and the technology has yet to be developed to carry out the unprecedented operation. As a result, Tepco says it will not be able to begin removing melted fuel from those reactors until 2020 at the earliest.