Mission to remove used fuel complete at Fukushima

A year-long operation to remove all the used fuel assemblies from the storage pool at the damaged Fukushima Daiichi unit 4 has been successfully completed. Some fresh fuel remains in the pool, but this should be removed by the end of the year.

A year-long operation to remove all the used fuel assemblies from the storage pool at the damaged Fukushima Daiichi unit 4 has been successfully completed. Some fresh fuel remains in the pool, but this should be removed by the end of the year.

The cask holding the last used fuel assembly is moved to the shared storage pool (Image: Tepco)

The last of the 1331 used fuel assemblies at the unit were removed and transferred to a common pool in a separate building on 5 November, Tokyo Electric Power Company (Tepco) announced.

Since last November, the used fuel assemblies in unit 4's storage pool have been removed one by one from storage racks and placed into a transportation cask. This has then been moved across the site to be unloaded at the site's shared storage facility. This process was repeated a total of 63 times until all the used fuel had been removed from the pool.

The fuel removal process was suspended between 1 July and 3 September due to an annual inspection for the overhead crane used for the operation. It resumed on 4 September.

Tepco said the removal of the used fuel marks "a solid step toward the decommissioning of the plant."

Unit 4 was off line for maintenance at the time of the 2011 accident with its full core load of fuel, as well as used fuel from previous operation, stored in a fuel pool at the top of the reactor building. Although this meant there was no possibility of a reactor accident at unit 4, there was a risk of the pool overheating. The stability of the pool was then reduced by major structural damage to the building caused by the ignition of hydrogen that leaked through ventilation systems shared with unit 3. The building has since been reinforced, and heavy debris and rubble has been removed from its roof. The used fuel transfer operation was managed within a new cover over the building which includes all the fuel handling equipment of a normal nuclear power plant.

Some 180 fresh fuel assemblies remain to be transferred from unit 4's pool to the common pool. Tepco said that the transfer of this fuel will be easier "as the radiation levels in the new fuel rods are low enough to be handled manually." However, it added, "The task will be handled with the same vigilance and commitment to safety that has characterized the removal effort so far."

The removal of the unused fuel is expected to be completed by the end of December.

Researched and written
by World Nuclear News