Workers lower the last part of a semi-cylindrical covering on top of the No. 3 reactor building.
April 12, 2019
The operator of the crippled Fukushima No. 1 nuclear power plant will start removing nuclear fuel from the No. 3 reactor as early as next week through equipment controlled remotely due to high radiation levels inside the building.
This will mark Tokyo Electric Power Co.’s first attempt to remove spent fuel from one of the three reactors that experienced a meltdown during the 2011 nuclear accident.
All spent fuel has already been removed from the No. 4 reactor.
TEPCO workers will use remote control to remove nuclear fuel assemblies kept in the pool on the upper floors of the No. 3 reactor building.
Utility officials acknowledge that the process will not be easy, as they have no experience conducting such a dangerous task remotely.
The 566 nuclear fuel assemblies in the storage pool will be removed under a plan expected to take two years to complete.
TEPCO wants to remove the assemblies as quickly as possible owing to concerns that another major earthquake or tsunami could further damage the reactor building and equipment. The No. 3 reactor will also serve as a test case for eventually removing spent nuclear fuel from the No. 1 and No. 2 reactor buildings.
Under the plan, workers will be stationed in a control room about 500 meters from the reactor building and use remote control equipment while observing the process through monitors.
Each nuclear fuel assembly will be lifted and transferred to a special transport container that can hold up to seven such assemblies in water. The container will then be carried out of the reactor building by crane, which will then lower the container outside of the building to a trailer about 30 meters below at ground level.
As a hydrogen explosion blew off the roof of the No. 3 reactor building in the wake of the 2011 nuclear accident, a semi-cylindrical copper covering has been placed over the building to prevent radioactive materials from spreading when the spent nuclear fuel is being removed.
All 1,535 nuclear fuel assemblies at the No. 4 reactor building were removed by the end of 2014. Radiation levels were comparatively low so workers could enter the building to work on the removal.
A TEPCO official in charge of the process called the removal at the No. 4 reactor “normal operating procedures,” but admitted that remote control operations added a new dimension of difficulty.
The utility has experienced problems with the crane and other equipment to be used at the No. 3 reactor.
Under TEPCO’s plan compiled shortly after the nuclear accident, all spent nuclear fuel was to have been removed from all four reactors by the end of fiscal 2021.
“We do not believe the process will proceed with zero problems,” said Akira Ono, president of the Fukushima Daiichi Decontamination and Decommissioning Engineering Co.
The work at the No. 3 reactor will serve as a model for a similar process planned for the No. 1 and No. 2 reactor buildings to start in fiscal 2023.
Government and TEPCO officials have said they will consider a detailed plan for removing spent nuclear fuel from those two buildings after reviewing the work done at the No. 3 reactor building.
The two other reactor buildings present different hurdles for workers.
The top floor of the No. 1 reactor building is covered with debris from a collapsed ceiling and damaged crane, the removal of which has proved difficult. Workers have also confirmed that the lid on top of the containment vessel has shifted, meaning radiation levels inside the building are likely even higher than in the No. 3 reactor building.
It thus remains to be seen if the same equipment to be used for the No. 3 reactor can be used for the No. 1 building. To prevent leaking of radioactive materials, the lid for the containment vessel will first have to be moved back into place.
While the No. 2 reactor building did not suffer major structural damage, large amounts of radioactive materials are believed to be trapped inside the building, meaning radiation levels are also very high there.
The level at the top floor is so high that any worker remaining there for one hour would quickly exceed the annual radiation exposure level. After decontamination, the upper part of the No. 2 reactor building will have to be taken apart to remove the spent fuel. However, this poses the major problem of preventing the spewing of radioactive materials during that process.
“To be honest, it will be difficult to say that no problems will emerge that will force a change in plans,” said Toyoshi Fuketa, chairman of the Nuclear Regulation Authority.