Tokyo Electric Power Co. said Friday that it has finished transferring the first batch of fuel rod assemblies from the Fukushima No. 1 plants reactor 4 spent fuel pool to another building with more stable storage conditions.

“All of the fuel assemblies have been placed in the storage rack (inside the common pool), meaning the first fuel transfer work effectively ended,” Tepco official Noriyuki Imaizumi told a press conference.

After reviewing the work flow that started Monday, the utility will move on to retrieve the next batch of fuel assemblies from the spent fuel pool of the damaged reactor 4 building.

The pool contains over 1,000 fuel assemblies and the process is expected to continue through the end of next year.

To get used to the operation, workers commenced with the removal of unused fuel assemblies, but they will also have to take out spent fuel, which is more difficult to handle because it is highly radioactive and emits heat as radioactive elements in the fuel decay.

The process starts with the transfer of fuel assemblies inside the water-filled spent fuel pool one by one into a transport container also placed inside the pool.

Once the container is filled with 22 fuel assemblies, workers lower it by crane from the fifth floor of the building where the pool is located so that it can be taken to the common pool about 100 meters away.

During the 2011 nuclear crisis, reactors 1 to 3 experienced core meltdowns, while unit 4 only suffered a hydrogen explosion as all of its fuel was stored in the spent fuel pool because the reactor was undergoing periodic maintenance work at the time.

However, the condition of the spent fuel pool on the highest floor of the crumbling building was a major source of concern in the early days of the crisis, as the water level was suspected to have dropped low enough to expose the fuel. Tepco later said the fuel in the reactor 4 pool probably did not sustain major damage.