information about Fukushima published in English in Japanese media info publiée en anglais dans la presse japonaise
19 Novembre 2013
November 19, 2013
http://ajw.asahi.com/article/views/editorial/AJ201311190036
Tokyo Electric Power Co. has started removing spent and unused nuclear fuel from the No. 4 reactor building at the Fukushima No. 1 nuclear plant. This is an important step to lessen the danger posed by the nuclear complex, which was wrecked in the 2011 earthquake and tsunami disaster.
The operation will likely take more than a year to complete. Even then, it will not dramatically change anything. Underground water continues to flood the crippled No. 1 to No. 3 reactors, making it radioactive.
The electric power industry and the government must not attempt to delude the public by stressing progress in just one aspect of the huge challenge that lies ahead. They must make utmost efforts to explain the overall picture. There is no room for even the slightest exaggeration.
The No. 4 reactor was offline for a regular safety inspection when disaster struck. So unlike the No. 1 to No. 3 reactors, the No. 4 unit did not have a core meltdown. However, the No. 4 reactor building was ripped apart by an explosion of hydrogen that apparently leaked from the No. 3 reactor.
There are 1,533 nuclear fuel assemblies in the storage pool, located in the upper part of the No. 4 reactor building. The figure compares with the 1,496 assemblies that were in the No. 1 to No. 3 reactors.
These bundled pellets of uranium fuel in the assemblies must be kept cool as they generate intense heat. If the storage pool loses its water, the fuel assemblies could overheat and cause a fire. If this happened, a vast amount of radioactive materials--including plutonium--would be released into the atmosphere, causing the situation to spin out of control.
As aftershocks have continued to jolt the Fukushima plant, the need to remove nuclear fuel from the unstable No. 4 reactor building has taken on increased urgency.
To accomplish this task, special equipment had to be created from scratch to pull the fuel assemblies out of the pool as well as a crane to load them onto vehicles for transportation.
That is why it has taken 2 years and eight months after the accident for the fuel removal operation to begin.
The work involves sinking a cask receptacle that can hold 22 assemblies into the pool and arranging assemblies with utmost care into the container one by one. The receptacle must then be transferred to a more secure shared pool some 100 meters away. The utility plans to finish the transfer of all the fuel assemblies from the No. 4 unit by the end of 2014.
Experts have voiced concerns about the fuel removal operation, which “involves a high degree of risk potential,” according to Shunichi Tanaka, chairman of Nuclear Regulation Authority. “In a sense, it is more risky than the radioactive water crisis,” he said.
Workers engaged in the operation face a high risk of being exposed to radiation. To secure skilled workers for the operation, proper monitoring of the dose levels and management of working conditions are even more vital.
The priority must be on ensuring absolute safety, not on meeting the schedule.
As for the No. 1 to No. 3 reactors, it is still unclear when the removal of nuclear fuel in the storage pools can start. Dealing with the melted fuel in the reactor cores requires developing special technologies.
What has started at the No. 4 unit is actually just one risky and delicate part of the complicated, multifaceted challenge of cleaning up the mess at the Fukushima No. 1 plant.
Transferring the fuel assemblies to the shared pool is not the end of the story. Eventually, it will be necessary to figure out a safer way to store the nuclear fuel, such as dry cask storage, which doesn’t carry the risk of the loss of water.