Here is a brief reminder of the facts of the worst nuclear disaster since Chernobyl (Ukraine) in 1986 and the challenges that remain.

The damage

Three of the plant's six reactors - Units 1, 2 and 3 - were in operation when the tsunami, following a powerful undersea earthquake, swept through on March 11, 2011. Their cooling systems failed when waves flooded the emergency generators, causing the cores of all three reactors to melt.

Hydrogen explosions in Units 1, 3 and 4 also caused significant damage, still visible in various places, such as the ruins of the metal frame at the top of Unit 1.

The Fukushima nuclear disaster in 2011 John SAEKI AFP

Roofing work continues using cranes, while workers in coveralls and equipped with dosimeters operate other machines.

Green corridors painted along the roads indicate where they can walk without reinforced protective equipment.

fuel rods

At the time of the accident, all six reactors had spent fuel rods in cooling pools.

The bars have been removed from two units and the process is ongoing in units 5 and 6, undamaged.

But in reactor No. 1, large quantities of radioactive rubble must be cleared beforehand.

To avoid spreading radioactive dust, the workers are installing a new roof and thus the extraction of the rubble should only start around 2027.

The Fukushima Dai-ichi nuclear power plant in Okuma, Fukushima prefecture, Japan, March 5, 2022 Charly TRIBALLEAU AFP / Archives

In Unit 2, radiation levels are so high that plant operator Tepco plans to access the bars by sending robots from two elevated platforms, one of which has already been built.

The removal of the bars is expected to begin there around the spring of 2024.

Molten fuel debris

In units 1 to 3, reactor fuel and other materials melted and then solidified into highly radioactive debris, a huge puzzle that Tepco has been working on for seven years now.

"We started examining the interior of reactor No. 1 in February" and "we expect reactor No. 2 to be the first from which we will remove fuel debris this year," Keisuke Matsuo told AFP. central communication officer.

Storage of contaminated water at the Fukushima Dai-ichi nuclear power plant in Okuma, Fukushima prefecture, Japan, March 5, 2022 Charly TRIBALLEAU AFP / Archives

Developed in the UK by Veolia Nuclear Solutions and Mitsubishi Heavy Industries, the more than 20-meter-long robotic arm that will be used for this mission was delivered last July after a delay due to the pandemic.

It is currently being tested.

contaminated water

The plant generates an average of 140 m3 of contaminated water per day, due to bad weather, groundwater and cooling water.

Tepco concreted floors, installed pumps and built an underground ice wall, but the problem persists.

The water is recovered and filtered to remove various radionuclides, but not tritium which cannot be removed with existing technologies.

Also 1.29 million tons of water are currently piling up in more than a thousand white, gray and blue tanks on the site of the power plant, whose storage spaces are expected to be exhausted within about a year.

Under a government plan, the water is to be diluted to reduce tritium levels before being released into the sea via a mile-long underwater pipe, a process expected to take many years. many years.

Although it has been approved by the International Atomic Energy Agency (IAEA), this project is criticized by neighboring countries of Japan, environmental NGOs and local fishing communities.

"We think the treated water is safe," says Matsuo, but "we can't start releasing the water without buy-in from those who will be affected."

A pharaonic invoice

The total cost of dismantling, which should last 30 to 40 years, is currently estimated at 8,000 billion yen (63.5 billion euros), which Tepco says it can cover.

But this figure does not include the cost of treatment and disposal of contaminated water.

© 2022 AFP