21 Nov (NucNet): Tokyo Electric Power Company (Tepco) has successfully moved a cask containing 22 fuel assemblies from the spent fuel pool at Fukushima-Daiichi-4 to safe storage in a common fuel pool.
Tepco said the fuel assemblies were loaded into the specially designed cask from 18-19 November. The cask was then decontaminated and transported today to the common spent fuel pool at 13:20 local time.
The work to remove 1,533 fuel assemblies from the Unit 4 spent fuel pool will now be paused for a scheduled safety review of procedures and methods, Tepco said.
Tepco said last week that 1,331 of the fuel assemblies are used and 202 unused, and their removal to long-term onsite storage is expected to take until the end of 2014.
Unit 4 at Fukushima-Daiichi was shut down for a regular inspection when the plant was hit by an earthquake and tsunami in March 2011 and all spent fuel assemblies had been transferred to the spent fuel pool. The unused assemblies were being prepared to be inserted into the reactor when the disaster happened.
Removing fuel assemblies from a fuel pool is “a normal operation”, Tepco said, but because of damage caused by a hydrogen explosion at Unit 4 after tsunami and earthquake, the job entails a risk that is “clearly different from normal operations in terms of working environment”.
One particular issue is debris that has fallen into the pool and could not be completely removed because it sits between the fuel racks and the assemblies. Tepco said that to avoid this debris causing any damage to the fuel elements during removal, the process would proceed slowly and be carefully monitored.
Tepco said the removal of the fuel assemblies is necessary because they are sitting in a storage pool that is above ground and in a heavily damaged building that had to be stabilised before beginning the removal. Removal of the assemblies will “lay the groundwork” for decommissioning and remediation work at the plant, Tepco said.
Tepco said that in December 2012 it conducted a seismic safety evaluation of the Unit 4 reactor building, which showed that even in the event of a major earthquake the earthquake resistance of the reactor building and the spent fuel pool is adequate.
