TOKYO, Japan (Xinhua) — While Japan yesterday marked the sixth anniversary of the 2011 earthquake and tsunami and the subsequent Fukushima nuclear disaster, how the aftermath has been dealt with has drawn much attention and concern from all over the world.

Tokyo Electric Power Company Holdings Inc (TEPCO), operator of the crippled Fukushima Daiichi nuclear plant, has said it plans to decommission the reactors in about four decades.

However, the difficult tasks such as processing contaminated water, cooling the reactors, and removing nuclear fuel and debris continue to pose serious challenges to the power company as well as the Government.

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 were rendered useless.

TEPCO has, since the disaster, successfully decommissioned the number 5 and 6 reactors at the plant, and more than 1,500 fuel rods in the number 4 reactor have been taken out and safely stored.

But removing the melted nuclear fuel rods from the number 1-3 reactors poses the biggest challenge yet to the decommission work, according to experts, and TEPCO, apparently, has not yet come up with a viable solution.

Naohiro Masuda, head of the decommissioning unit of TEPCO, told Xinhua recently that TEPCO will come up with a plan after discussions with the Government this summer, but how the plan will proceed is not yet clear.

One of the difficulties lies in the extremely high radiation levels inside the reactors, and the fact that the actual condition of the melted fuel inside the reactors remains unknown.

The operator of the crippled power plant said last month that levels of radiation as high as 650 sieverts per hour were detected inside the number 2 reactor, much higher than an earlier reading of 73 sieverts per hour in 2012. The amount of radiation is enough to kill a person, even after being exposed for just a brief period of time.

Even robots sent to gather information in the damaged reactor suffered malfunctions and failures, possibly due to extremely high levels of radiation.

The power company said on Thursday that it will attempt to examine the inside of the number 1 reactor next Tuesday using another remote-controlled robot, following a failure last month to robotically look into the number 2 reactor.

There have also been concerns that the melted nuclear fuel residue is eroding the concrete bottom of the safety shell of the reactors, having already penetrated the reactor pressure vessel.

Masuda denied such a possibility, however, saying that "although we don’t have direct confirmation about the concrete bottom of the safety shell, based on other information, we think the residue has not eroded through the bottom".

"The bottom might have been eroded by 50 or 60 centimetres, but it is as thick as two or three metres, so there is no need to worry," he added.

To keep the number 1 to 3 reactors cooled, TEPCO has to inject a large amount of fresh water into them 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, and now there is close to one million tons of ‘decontaminated’ water stored in giant steel tanks at the nuclear plant, and the amount of water is increasing.

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 yet enough scientific research to determine the effects of the contaminated water on the sea.

TEPCO has also tried to build a frozen soil wall around the crippled nuclear plant, to prevent groundwater from flowing into the facilities and getting contaminated.

The wall was built by driving around 1,500 steel pipes 30 metres into the soil around the perimeter surrounding the Number 1 to 4 reactors and then pumping liquid calcium chloride at minus 40 degrees Celsius into the pipes to freeze the surrounding soil.

The wall reportedly melted in two places following powerful typhoons last September, raising concerns over the efficacy of such an unprecedented and expensive approach.

According to Japan’s Ministry of Economy, Trade and Industry, the cost of the decontamination work, including soil and tree removal, is expected to surge to 4 trillion yen (US$35 billion).

The unprofitable project has also led to an increase in corruption, as evidenced recently by a 56-year-old Environment Ministry employee arrested on suspicion of accepting a bribe.

The employee was found to have given favourable treatment to a construction company in the allocation of clean-up work in Fukushima Prefecture, after he was treated with nice dinners and free trips.

The case is only "the tip of the iceberg", according to local media, as there have been a lot of rumours about corruption connected to the multitrillion-yen decontamination project.

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