The process of removing all 566 fuel assemblies from the storage pool of unit 3 at the damaged Fukushima Daiichi nuclear power plant in Japan was completed on 28 February, Tokyo Electric Power Company (Tepco) has announced. Fuel assemblies have already been removed from the pool at unit 4, but such work has yet to start at units 1 and 2.

The fuel removal facility above unit 3's reactor building (Image: Tepco)

The removal of fuel from unit 3's storage fuel pool began on 15 April 2019 after several years of work to remove debris from the reactor building service floor and prepare for this work to reduce the hazard at the accident site. Tepco's aim was to complete the fuel removal during fiscal year 2020 (ending March 2021), in accordance with its mid and long-term roadmap.

The company announced yesterday that the final six fuel assemblies from the used fuel pool had been removed from their transport containers and placed into the fuel rack in the common storage pool, thereby completing this project.

The section of the reactor building that sheltered the service floor of unit 3 was wrecked by a hydrogen explosion three days after the earthquake and tsunami of 11 March 2011 - leaving the fuel pond exposed and covered with debris, including many twisted steel beams.

Tepco said the removal of fuel from unit 3's storage pool consisted of a series of preparatory tasks that were completed one by one, such as: the removal of rubble from, and decontamination of, the uppermost floors of the reactor building; the construction of a fuel removal cover; and, the installation of a fuel handling machine. Since all of these tasks had to be performed in a high-dose environment, remotely operated equipment was used to remove debris whilst removing fuel.

"This was the first time such methods were attempted and there were various problems that had to be overcome," Tepco said.

Tepco constructed a separate structure to facilitate the removal of fuel from unit 3's storage pool by a remotely-operated crane. This 54-metre-tall structure includes a steel frame, filtered ventilation and an arched section at its top to accommodate the crane. Measuring 57m long and 19m wide, it is not fixed to the reactor building itself, but is supported on the ground on one side, and against the turbine building on the other.

The company completed the removal of 1331 used assemblies from the storage pool at unit 4, which had suffered much worse structural damage, by the end of 2014.

Tepco said the "knowledge and lessons learned" from the removal of fuel at unit 3 "will be leveraged during the upcoming fuel removal from the unit 1 and unit 2 used fuel pools as we continue to steadily move forward with decommissioning whilst prioritising safety."

Researched and written by World Nuclear News