A "long and bumpy" path to decommissioning

7 Mars 2019

March 6, 2019

8 years on, and no quick fix in sight to reactor dismantling

http://www.asahi.com/ajw/articles/AJ201903060056.html

By CHIKAKO KAWAHARA/ Staff Writer

Time is slipping away as the government and Tokyo Electric Power Co. continue to grope with the formidable challenge of decommissioning the crippled Fukushima No. 1 nuclear plant.

Already, more than one-fifth of the 30 to 40 years estimated for the work has passed without any discernible leap forward on the issue.

“We no longer face a situation of having to quickly respond to a slew of rising problems like a whack-a-mole machine,” said a TEPCO official, referring to the aftermath of the 2011 nuclear disaster and incremental steps in progress since then.

For example, reporters decked out in full protective gear were allowed to visit the central control room for the No. 1 and No. 2 reactors in February. The room, dimly-lit, is now tidied up.

When the crisis unfolded at the plant after the Great East Japan Earthquake and tsunami hit on March 11, 2011, the room was a hive of activity with 24 people present.

Today, many gauges filling walls of the room bear signs saying “Unusable.” Figures scribbled down by technicians were left on the wall next to a water level indicator, a frantic effort to grasp of what was happening inside the No. 1 reactor’s pressure vessel after cooling systems were knocked out.

The path to decommissioning bears all the signs of being long and bumpy.

Plant operator TEPCO is tasking with finding solutions to a host of challenges to complete decommissioning, including how to remove melted nuclear fuel from the crippled reactors.

Radiation levels at the No. 1 and No. 2 reactor buildings are still too high for workers to enter. Melted nuclear fuel remains intact inside those reactors.

Retrieval of the nuclear fuel debris, which is scheduled to start in 2021, is considered to be the primary hurdle for the utility, a challenge that will determine success or failure of the overall decommissioning program.

Albeit slowly, though, conditions inside the reactors have been revealed by investigations with the use of remote-controlled probes.

A probe in the No. 2 reactor’s containment vessel in February succeeded in making "first contact" with fuel debris.

The device, not unlike a prize-grabbing crane machine at a game arcade, was able to lift pebble-like radioactive debris.

The problem is that such small melted fuel represents only a portion of the entire debris. The rest rests on the bottom of the containment vessel, and removing it from the reactor building poses immense hurdles.

Also, no decision has been made on where to store and dispose of the fuel debris even if the company manages to remove the stuff.

In the case of the No. 3 reactor, the building is now covered with a canopy to prevent radioactive substances spewing into the atmosphere. The top floor of the building blew up in a hydrogen explosion triggered by the meltdown.

Workers in protective gear are busy training for the day they start removing spent nuclear fuel from the storage pool at the No. 3 reactor building. A huge crane moves left to right when a siren sounds.

A combined 1,573 spent nuclear fuel assemblies were stored in the storage pools of the No. 1 through No. 3 reactor buildings.

Moving the fuel to somewhere safe has taken on added urgency since the buildings, already damaged by the quake, tsunami and nuclear accident, could collapse if another major temblor and tsunami strike the nuclear complex.

The transfer of all spent fuel from the No. 4 reactor building, which had been shut down before the 2011 disaster, was completed in December 2014.

But work at the No. 3 reactor building was significantly delayed by the project to install a canopy and decontaminate the structure, which took longer than expected. The crane used for the work also malfunctioned, adding to the delay.

Removing spent fuel from the No. 1 and No. 2 reactor buildings is expected to start in fiscal 2023.

Sprawling woods that existed at the nuclear complex prior to the disaster were transformed into a vacant lot for row after row of tanks storing radioactive water produced by cooling the crippled reactors.

There are now about 950 storage tanks, holding more than 1 million tons of contaminated water.

No decision has been made on how to dispose of the contaminated water although the plant is nearing its capacity to keep storage tanks on its premises.

Still, cleanup work over the past few years has freed up some space for workers on-site.

Starting from last year, workers can walk between the No. 2 and No. 3 reactor buildings in just a helmet and a simple respirator mask, gear that is considerably lighter than when radioactive levels were extremely high.

The increased mobility makes it easier for them to go about their tasks.

Radiation levels there hover at between 200 and 300 microsieverts per hour, which means workers have less than a five-minute window to take a break if they stop due to health risks.