Risk in Fukushima No. 4 reactor mitigated as last of nuclear fuel removed

OKUMA, Fukushima Prefecture--Tokyo Electric Power Co. removed the last four nuclear fuel assemblies that remained in the No. 4 reactor building of the crippled Fukushima No. 1 nuclear power plant from its storage pool on Dec. 20.

The No. 4 reactor was offline at the time of the March 11, 2011, Great East Japan Earthquake and tsunami. However, an explosion occurred in the building four days later, seriously damaging it.

After the accident, experts pointed to the risk of nuclear fuel in the pool melting from insufficient cooling and releasing a large amount of radioactive materials. However, the threat has been mitigated with the removal of the last assemblies.

On Dec. 20, TEPCO allowed the media to watch the removal work.

Workers pulled up from the pool a cask containing the last four unspent nuclear fuel assemblies. They plan to transfer it to the No. 6 reactor building, which sustained relatively minor damage in the disaster, within a few days after decontaminating the outside of the cask.

The transfer will mean that all of the nuclear fuel in the No. 4 building has been removed from the building as scheduled by year-end.

The pool had held a total of 1,535 nuclear fuel assemblies, which consisted of 1,331 spent and 204 unspent nuclear fuel assemblies.

TEPCO started the removal of those assemblies from the pool in November 2013 after installing a new roof and a crane on the building. The removal of spent nuclear fuel assemblies concluded in November this year.

There will be no work in the No. 4 reactor building for the time being. TEPCO will be engaged in efforts at the No. 1, No. 2 and No. 3 reactor buildings and in dealing with the growing volume of contaminated water partly resulting from efforts to keep the reactors from overheating.

(This article was written by Yu Kotsubo and Hiromi Kumai.)