Plans for the removal of nuclear fuel from Fukushima Daiichi 4 have been explained by Tokyo Electric Power Company (Tepco).
Unit 4 is heavily damaged and the used fuel pond has had to be supported by the installation of steel beams and concrete. The pond also contains more fuel than the others on site because the entire core load of fuel had been stored there for maintenance work when the natural disasters struck on 11 March 2011.
For these reasons unit 4's pond represents one of the biggest hazards on the site, and tackling it by removing the fuel is one of Tepco's highest priorities. This is greatly complicated, however, by the contamination and damage of equipment normally used for this purpose and the many tonnes of wreckage on top of the reactor building as a result of the ignition of hydrogen. To remove the fuel, therefore, Tepco will have to finish clearing the debris and then create new shelters fitted with the proper equipment for the work to take place.
Work has already started on a cover for unit 4's reactor building and the company said today it plans to construct another 53 metre steel beam structure alongside and over the top of this, enclosing most of the reactor's service floor. It will protect the used fuel pond and the equipment used to remove fuel from the pond and package it. The fuel will be packaged for transport the short distance to the site's shared fuel pond, although it will also need to be inspected and flushed clean of dust and debris.
The extra building structure will be clad in steel with a weatherproof covering. Tightly sealed, it will feature filters to control the movement of fine radioactive particles. Air supplied to the building will be filtered on the way in and on the way out.
Tepco's diagrams showed the building is supported by an 'improved foundation' and the company said it would be constructed to standards 50% higher than Japanese earthquake codes. Equipment within will be operated from a remote earthquake-proof building with feedback from numerous radiation detectors in the filtration system.
The timescale for this project depends on Tepco's success in removing the roof-top debris, which is ongoing and expected to conclude in the second quarter of this year. Work is starting now on the new buildings and these could be finished with equipment fully installed in the second quarter of 2013. The target to actually begin removing the fuel is the latter part of 2013.
Researched and written
by World Nuclear News