All systems ready for Fukushima fuel removal

Wednesday, 13 November 2013

Engineers at Fukushima Daiichi have done final checks before they begin removing fuel from unit 4's storage pond, the highest priority safety-related task in the site's decommissioning.

Technicians within the new building cover. The empty reactor vessel is beneath the circular section, the rectangular part is the used fuel pool (Image: Tepco)

 
A fuel transport container will be placed in the pool using the main crane. Workers will then use the smaller refuelling crane to move fuel assemblies one by one from their vertical storage racks to the container. When this is full it will be sealed, lifted from the water by the main crane, placed on the service floor for decontamination and then taken through a special route to a vehicle that will move it across the site to be unloaded at the site's shared storage facility. This process will be repeated until the pool is empty.

With a total of 1533 fuel assemblies in the pool (1331 used, 202 unused) this is expected to take until the end of 2014. Tepco will move the fuel during the day and clean dust and debris from the pool water during the night. Two containers will be used in relay.

One of the fuel containers pictured during training tests (Inage: Tepco)

 
The Nuclear Regulatory Authority granted its approval for the security and radiological protection aspects of the work yesterday, and Tepco engineers conducted final functional checks of the cranes using non-radioactive dummy fuel today. One more round of feedback from local people is required before the operations begin, perhaps as soon as next week.

Inspecting the controls of newly-installed cranes (Image: Tepco)

 
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 thousands of tonnes of debris and rubble have been removed from its roof. The new cover has been constructed with all the fuel handling equipment of a normal nuclear power plant and inspections of the pool have shown the fuel to be undamaged and not suffering from corrosion.

Researched and written
by World Nuclear News