Fukushima nuclear disaster and water release
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Fukushima nuclear plant's Nos. 1 to 4 reactor buildings on March 3, 2013 (left) and September 5, 2014 (right) respectively, showing work is under way to build underground ice walls around the basements of the buildings. Photo: Kyodo

Fukushima still a hazard due to melting ice plug, operator admits

Pouring ice into a tunnel at crippled nuclear plant has failed to keep water from seeping in

A plug of ice has failed to completely block the flow of groundwater into the basement of Japan's crippled Fukushima nuclear plant, leading to the continued risk of radioactive contamination, officials at Tokyo Electric Power (Tepco) have admitted.

Since early June, engineers from Tepco have been pouring hundreds of tonnes of ice into a tunnel, which was originally used to run cable into the reactor's turbine building, in an effort to freeze a section of the passage.

As well as stopping more water seeping into the basement, the scheme would have permitted the removal and treatment, either frozen or in liquid form, of water already contaminated.

But an official at the company said the project was not working as anticipated.

"We estimate that 92 per cent of the water in the trench is frozen, but that's not enough and water is still flowing," the official said.

"We are going to have to use additional technologies to halt the flow of water and we are holding discussions with the government about what to do."

A decision on a course of action would be announced early next month, he added. One proposal was to use more chemicals in the process, or even cement.

Engineers have been dumping 27 tonnes of ice into the trench every day, as well as injecting a further one tonne of dry ice in an effort to make it freeze solid.

When Tepco began the process of freezing the water in tunnels at the site, officials described the move as "a major milestone" in the decommissioning of the plant, which was devastated by a magnitude-9 earthquake and tsunami in March 2011.

Officials have also said the failure of the effort to freeze water in the tunnel is separate from the construction of an impermeable wall of soil frozen with chemicals. That ice wall on the landward side of the plant is meant to stop groundwater seeping into the reactor buildings and becoming contaminated before escaping into the Pacific Ocean.

"The difficulties encountered in freezing the contaminated water does not in any way represent a setback in development of the ice wall, for which construction is proceeding as planned," Tepco said in a statement.

But environmental campaigners are sceptical over whether the ice wall will work.

"We have to ask why they are pushing ahead with this plan when two of the three initial tests, which were carried out on the seaward side of the plant, failed," said Aileen Mioko-Smith, of Kyoto-based Green Action Japan.

"They have moved the construction to the landward side now and they say it is working, but I see no evidence that it will be effective," she said.

"And what if there is another earthquake?" she asked. "Even a minor one would damage the pipes and render the entire system useless."

Mioko-Smith also pointed to the massive initial cost of the system, plus the fact that the wall would consume the same energy as 13,000 ordinary households, at an annual cost of about a billion yen (HK$71.35 million).

Tepco's latest setback coincides with a large demonstration in Tokyo on Tuesday, with 16,000 people protesting against the government's plans to restart the nation's idled nuclear reactors.

This article appeared in the South China Morning Post print edition as: Fukushima still a hazard due to melting ice plug