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Saturday, 13 June 2015

INSIGHT: Success of revised decommissioning plan for Fukushima far from a done deal



Safety over speed reflects the thinking behind the revised road map for decommissioning the reactors at the Fukushima No. 1 nuclear power plant.

Officials of the central government and plant operator Tokyo Electric Power Co. had wanted in the past to move quickly in decommissioning the reactors in part because that would also speed up the rebuilding process in Fukushima Prefecture.

However, because of the unprecedented scale and nature of the decommissioning project resulting from the triple meltdown triggered by the 2011 earthquake and tsunami disaster, the rush to move on resulted in only more problems that had to be addressed.

The revised road map that got the official go-ahead June 12 delays the removal of nuclear fuel from the three reactors by as much as three years. The new schedule was needed because of the numerous problems that arose in the preliminary stages of work to prepare for the most difficult work of removing nuclear fuel assemblies from the spent fuel storage pools. An even more dangerous process that comes with its own larger set of unknown factors is removing the melted fuel in the reactor cores of the No. 1, No. 2 and No. 3 reactors.

One of the biggest problems has been removing debris at the plant site caused by the explosions at the reactors, along with decontaminating work areas with high levels of radiation, stopping leaks of radiation-contaminated water and dealing with radioactive materials that are still gushing.
The hurried pace of past work may have been a factor behind a spike in work-related accidents at the plant site.

New targets have been established for dealing with the continuing problem of contaminated water.
One goal is to reduce the flow of groundwater into the reactor buildings by the end of fiscal 2016 to less than 100 tons a day from the current daily level of about 300 tons.
However, achieving that goal will require successful operation of two separate projects. One is the construction of an underground frozen wall of soil to divert groundwater, while the other involves processing pumped up groundwater before releasing it into the ocean.

Even if the contaminated water problem is dealt with, there are other issues that have to be addressed before removal of the nuclear fuel from the reactors can begin.

The overall goal of completing the decommissioning within a period of 30 to 40 years has not changed. The road map also maintains the objective of starting the removal of melted fuel at one of the three reactors in 2021. To achieve that goal, the method for removing that fuel will have to be finalized in early fiscal 2018.

However, a major problem is the uncertainty about just where that melted fuel is located within the reactor containment vessel.

Remote-controlled robots will be used within the vessels to assess conditions there.
Hajimu Yamana, deputy head of the Nuclear Damage Compensation and Decommissioning Facilitation Corp. who is in charge of providing technological advice, said, "By using investigative robots to gather information, we will have a pretty good idea of the state of the melted fuel within two years. We should have all the information we would need by then in deciding how to remove the fuel."

But some experts still seem to think the authorities are rushing things.

Shigeaki Tsunoyama, former president of the University of Aizu in Fukushima Prefecture who serves as an adviser to the Fukushima prefectural government on nuclear issues, cast doubt on whether fuel removal could begin within three years of deciding the removal method.
He cited the problem of developing specialized equipment, training the workers to use it and screening by the Nuclear Regulation Authority as being time-consuming issues that would have a bearing on the outcome.

Source ; Asahi Shimbun
http://ajw.asahi.com/article/0311disaster/fukushima/AJ201506130054
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