TOKYO, March 11 (Xinhua) -- Seven years after one of the worst nuclear disasters in history, Japan is still struggling with the aftermaths, not only the tough tasks of reconstruction, but also nuclear cleanup work that is expected to take generations, with hefty costs and unsolved technical problems.

The massive earthquake and the ensuing tsunami on March 11, 2011 severely damaged three reactors at Daiichi facility in Fukushima, which suffered core meltdowns after their key cooling systems were knocked out and backup power supplies rendered useless.

Tokyo Electric Power Company Holdings Inc. (TEPCO), operator of the crippled Fukushima Daiichi nuclear plant, had since successfully decommissioned the No. 5 and 6 reactors at the plant, and more than 1,500 fuel rods in the No. 4 reactor had been taken out and safely stored by the end of 2014.

But the problem lies with removing the melted nuclear fuel and debris from the No.1 to 3 reactors, which, according to experts, poses the biggest challenge to the decommission work.

The Japanese government and TEPCO have made plans to start fuel removal from the three reactors in 2021, but experts have expressed doubts regarding whether the plan could be carried out as scheduled.

Toyoshi Fuketa, Nuclear Regulation Authority Chairman, told a press conference recently that the removal work has not yet reached a point where "exit is in sight."

One of the difficulties lies in the extremely high radiation levels inside the reactors.

TEPCO said last month that levels of radiation detected inside the No. 2 reactor in a January probe were as high as 7-42 sieverts per hour, still enough to kill a person for just a short period of exposure.

The operator of the crippled plant, having established the path of conducting the cleanup work through remote mechanic systems, is still struggling with finding more viable technical solutions to the process.

The whole process also comes with a hefty price tag. According to Japan's Ministry of Economy, Trade and Industry, the cost of the decontamination work and treatment of polluted water, is expected to surge to 8 trillion yen (75 billion U.S. dollars) in total.

The number was much higher according to the calculation of a civil group Atomic Energy Citizens' Committee, reaching roughly 30 trillion yen (281 billion U.S. dollars).

Other thorny problems include decontaminating the soil and treating the contaminated water.

To keep the No.1 to 3 reactors cooled, TEPCO has to inject a large amount of fresh water into the reactors constantly. The water becomes radioactive in the process and is then stored in the basement of the reactor buildings. TEPCO's "decontamination" facilities can remove radioactive cesium and strontium from the water but not tritium.

TEPCO released a limited amount of radioactive water into the Pacific Ocean after getting approval from the local fishery association in September 2015. But there is not enough scientific research to determine that dumping contaminated water into the ocean is safe.

Some much-vaunted measures turned out not as efficient as they were originally planned while costing a huge sum of the money.

A government-commissioned group of experts concluded recently that a costly underground ice wall is only partially effective in reducing the ever-growing amount of contaminated water at the nuclear plant.

The wall cost 34.5 billion yen (323 million U.S. dollars) to build and is expected to cost more than 1 billion yen (9.4 million U.S. dollars) annually in operating and maintenance.

Most of the hefty expenses would have to be borne by taxpayers, as TEPCO, which was bailed out by the government, has been grappling with difficult financial situations when coping with the lengthy task of decommissioning the plant and carrying out cleanup work which is likely to take decades.

The operator of the Fukushima Daiichi nuclear plant has also been hit with a number of lawsuits for alleged negligence or improper design, construction and maintenance of the nuclear facilities.

"The multiple disasters that struck Fukushima seven years ago are not something that just belongs to the past, but are still affecting us," said Fukushima Governor Masao Uchibori.