Tepco readies to install unit 3 cover

The installation of a protective cover over unit 3 of the damaged Fukushima Daiichi plant in Japan can start as soon as the removal of rubble from the reactor building is completed, Tokyo Electric Power Company (Tepco) said.

The installation of a protective cover over unit 3 of the damaged Fukushima Daiichi plant in Japan can start as soon as the removal of rubble from the reactor building is completed, Tokyo Electric Power Company (Tepco) said.

Sections of the cover at the Onahama works (Image: Tepco)

Plans were announced in November 2012 for a cover to be constructed to encase the unit's damaged reactor building, protecting it from the weather and preventing any release of radioactive particles during decommissioning work.

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.

The fabrication of the cover has been under way since November 2013 at the Onahama works in Iwaki city. It has been made in sections so that once it is transported to Fukushima Daiichi, the time to assemble it can be shortened and the radiation exposure to the workers on site can be significantly reduced, Tepco said.

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.

On 2 August, Tepco announced that it had removed the fuel handling machine, the largest remaining piece of rubble, from the unit's used fuel pool at the top of its reactor building. Its removal followed months of preparation and clears the way for the remaining rubble and the used fuel in the storage pool to be removed.

The assembly of the protective cover over unit 3 will start once all the rubble is removed.

Tepco said there are a total of 566 fuel assemblies inside the unit's pool and the cover will prevent radioactive substances from scattering during their removal.

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.

Researched and written
by World Nuclear News