The disaster that struck four years ago may have abated for most of the Tohoku region, but the nightmare continues at Tokyo Electric Power Co.’s Fukushima No. 1 nuclear plant, which suffered three reactor core meltdowns and is plagued daily by increasing amounts of radioactive water.

Tepco hopes to improve the situation via two key measures: a 1.5-km-long sunken wall of frozen soil encircling stricken reactors 1, 2 and 3 and the damaged reactor 4 building to keep groundwater from entering and mixing with coolant water leaking in the reactor building basements, and “subdrain” wells around the buildings to pump up the tainted groundwater for treatment and ultimate discharge into the Pacific.

The utility hopes these steps will drastically reduce the amount of radioactive water, which is currently some 300 tons each day.

Many experts, however, say Tepco can’t expect smooth sailing as a wall of underground ice of such magnitude has never before been attempted.

And Tepco’s plans to pump up tainted groundwater via the subdrains and discharge it into the sea after removing most of its radioactive components also appears iffy. The company has already lost the trust of fishermen over its failure to disclose the extent of the radioactive water flowing into the Pacific.

The crippled complex has to contend with some 300 tons of new tainted groundwater every day, and part of the process has entailed a nonstop effort to build steel storage tanks. The groundwater, mainly rain that seeps into the soil both at the complex and at locations farther inland, flows toward the sea, including into the basements of the buildings housing the three wrecked reactors.

There, the groundwater mixes with radioactive water that is leaking from cracks in the reactors. Tepco must keep pumping new water into the reactors to cool the melted fuel rods within. The basements are too radioactive to enter.

The problematic groundwater flow used to amount to 400 tons daily, but the utility has taken some steps, including paving over part of the complex with asphalt to keep rainwater from seeping underground.

To stop the increase of tainted water, Tepco must keep all, or at least nearly all, groundwater from flowing into the basements.

The sunken ice wall is considered critical to this goal and Tepco has been setting up pipes to run coolant underground to freeze the soil — a process the utility hopes to start at the end of this month if it receives approval from the Nuclear Regulation Authority.

Although Tepco said it will take several months to completely freeze the soil into a solid ice wall, it expects the wall to reduce the amount of groundwater flowing into the reactor buildings to 50 tons a day from 300 at present.

One “problem will be how long it will take to freeze soil evenly (to make an ice wall without holes), and we have already seen this problem when Tepco attempted to make ice walls inside the underground trench (connected to the reactor turbine buildings),” said Shigeaki Tsunoyama, an education and research special adviser at the University of Aizu.

“I’m worried that the same thing might happen with the ice wall (encircling the reactor buildings),” said Tsunoyama, who sits on a panel formed by the NRA to oversee the decommissioning of the nuclear plant.

Fukushima No. 1 has a maze of underground trenches connected to the reactor turbine buildings to run cables and pipes, and they are now filled with highly radioactive water leaking from the turbine buildings.

To remove the water in the trenches, Tepco tried for months to block the tainted water running from the buildings by freezing it before abandoning the effort last year.

Kiyoshi Takasaka, an adviser on nuclear issues to the Fukushima Prefectural Government, also said there are many unknown technical factors regarding the ice wall, including areas where the uneven groundwater flow is fast and underground cable and pipe conduits that may impede the freezing effort.

Then there’s the plan to pump up groundwater from dozens of subdrain wells built around the reactor buildings and dump it into the sea.

This is different from the so-called groundwater bypass, which is already underway and aimed at intercepting clean groundwater before it arrives at the plant and pumping it into the ocean directly.

If the subdrain well plan works effectively along with the ice wall, Tepco estimates it will be able to effectively stop the groundwater from reaching the reactor buildings.

Ending the increase is a pressing issue because the utility has been endlessly making tanks to store the tainted water at the site, and some of those tanks have leaked.

Tepco already has more than 500,000 tons of tainted water on its hands. As this amount grows, so does the possibility of leaks. Also, the amount of high-level radioactive waste derived from the cleaning process will also increase.

Meanwhile, the groundwater pumped up from some of the subdrain wells likewise contains highly radioactive materials.

Tepco says it will scrub the water with treatment systems to lower the levels of radioactive substances to less than the legal limits before discharging it into the sea.

This plan was authorized by the NRA in January, but Tepco has been unable to get fishermen to approve it.

People in Fukushima “do not want Tepco to dump the water into the sea. The most troubling thing is . . . harmful rumors,” said Tsunoyama, who is also an adviser to Fukushima Prefecture on nuclear issues.

“You can’t really persuade people to ignore harmful rumors,” he said.

The subdrain well plan is also not a cure-all, as it was revealed last month that Tepco knew radioactive rainwater has been leaking from the roof of a reactor building into the sea since last spring but did not think it necessary to disclose this information.

Some of the fishery groups in Fukushima were about to agree to the plan, but Hiroshi Kishi, chairman of the National Federation of Fisheries Cooperative Associations, said fishermen no longer have any trust in the utility — and this will make it even harder for Tepco to get them on board.

Tsunoyama and Takasaka both said Tepco won’t be able to start the subdrain well plan anytime soon, so the ice wall will be a vital step in slowing the increase of radioactive water.

Takasaka said that although such an ice wall has been used before in civil engineering work, the scale of the project at Fukushima No. 1 will be unprecedented.

Takasaka and Tsunoyama said Tepco’s measures have tended to be ad hoc, so it has always had to come up with extra measures. The utility must make careful plans, including identifying spots expected to be tough to freeze, and take precautions to avoid unexpected problems in creating the ice wall, they said.