Tokyo Electric Power Company (Tepco) has examined two unused fuel assemblies from the fuel storage pool at unit 4 of the Fukushima Daiichi plant and found no significant damage. A further 200 unused assemblies remain in the pool, alongside over 1300 which have been used.
|Top: Workers inspect an unused fuel assembly from the pool. Left: A small amount of corrosion is found on the fuel. Right: Debris found between some of the fuel rods
Unit 4 was offline for regular maintenance when the 11 March 2011 earthquake and tsunami struck, meaning that its full inventory of nuclear fuel was stored in the used fuel pool at the time. Four days after the natural disasters, the top part of the reactor building, where the fuel pool is housed, was destroyed by a hydrogen explosion followed by a fire. The pool contains 1533 fuel assemblies. However, 202 of these have never been used in the reactor and are not significantly radioactive and do not generate heat, making them easier to handle.
Tepco removed two of the unused fuel assemblies from pool in mid-July. The company has now completed visual inspections of them and found no significant damage or corrosion. Grit found between the fuel rods in the assemblies is believed to be debris from the damaged concrete walls of the reactor building.
The relatively large amount of nuclear fuel in the pond has made unit 4 one of the top priorities for Tepco in assuring overall safety of the site. The pond has been covered with a steel platform.
Tepco plans to build an airtight secondary structure alongside and over the top of unit 4 to enable engineers to safely remove nuclear fuel from the pond. As part of its plan to decommission the Fukushima Daiichi site, the company expects to begin removing all the fuel assemblies from the storage pool in December 2013.
Researched and written
by World Nuclear News