Protecting unit 3

Tuesday, 20 November 2012

Plans for the construction of a protective cover over the damaged reactor building of Fukushima Daiichi unit 3 have been announced by Tokyo Electric Power Company (Tepco).

How the completed cover and defueling structure could appear (Image: Tepco)

The section of the reactor building that sheltered the service floor of unit 3 was wrecked by a hydrogen explosion three days after the tsunami of March 2011 - leaving the fuel pond exposed and covered by debris including many twisted steel beams. Concrete dust in the pool has made the water very murky and the debris inside inhibits the flow of water.

The cover will be constructed to encase the damaged reactor building, protecting it from the weather and preventing any release of radioactive particles during decommissioning work. A separate structure will be built to facilitate the removal by crane of used fuel from the storage pool. This 54-metre-tall structure will include a steel frame, filtered ventilation and an arched section at its top to accommodate the crane. Measuring 57 metres long and 19 metres wide, it will not be fixed to the reactor building itself, but will be supported on the ground on one side, and against the turbine building on the other. Tepco noted that the steel-clad structure would be built to standards 50% higher than Japanese earthquake codes.

Construction of the cover and defueling structure over unit 3 is expected to start as soon as debris removal has been completed from the top of the reactor building.

Tepco aims to remove sufficient debris from unit 3's used fuel pool to allow the removal of the fuel assemblies to start in fiscal 2014.

The fuel removed from unit 3 will be packaged for transport the short distance to the site's communal fuel storage pool, although it will need to be inspected and flushed clean of dust and debris.

Fukushima Daiichi unit 1 has already been covered, and work is underway for a similar cover at unit 4.

Researched and written
by World Nuclear News