Reducing contamination risk vital in Fukushima N-plant deactivation

Reducing contamination risk vital in Fukushima N-plant deactivation

Decommissioning operations have made some progress, but many hurdles remain. The work will take as long as 40 years to complete, and it is essential to overcome challenges one by one.

The cores of Nos. 1, 2 and 3 reactors were damaged in the accident, and the No. 4 reactor building collapsed in an explosion caused by hydrogen that leaked from the No. 3 reactor. The extraction of nuclear fuel from the cooling pool of the No. 4 reactor was completed late last month.

Now that the wreckage of the building that housed the No. 3 reactor has been removed, the operation to extract nuclear fuel will start. The work must be carried out steadily to reduce the risk of contamination.

The amount of radioactive contaminated water generated daily at the plant has dropped from 400 tons to 300 tons in the past year. The amount has declined because groundwater from wells is being pumped up before it flows into the reactor buildings and is discharged into the sea.

In a bid to further reduce the generation of contaminated water, TEPCO has been building a frozen-soil wall to prevent the inflow of water by freezing the soil around the reactor buildings. There is also a plan to purify the groundwater generated nearest to the buildings before discharging it into the sea. This must be realised quickly.

A series of unexpected problems must be dealt with properly.

TEPCO’s handling insufficient

It came to light last month that radioactive rainwater was leaked into the sea through a drainage canal. TEPCO has come under heavy criticism for not making public the related data, and negotiations with the fishermen concerned over additional discharging of groundwater into the sea have hit a snag.

The utility did not consider that the data on rainwater generated in a natural phenomenon was subject to publication. In hindsight, it must be said that TEPCO’s handling of the matter was insufficient. The utility is urged to check again whether there are any undisclosed data.

The disposal of contaminated water stored in the plant’s compound has been delayed despite the progress of measures to prevent the generation of contaminated water.

About 1,000 tanks store more than 600,000 tons of contaminated water, and no more space will become available in the near future for installation of additional tanks. It is feared that radioactive contamination could spread if the existing tanks are damaged in an earthquake or other natural disaster.

It is also feared that if so many workers continue to be assigned to monitoring the tanks, decommissioning work as a whole will be delayed.

It is imperative to stabilise the operation of contaminated water purification equipment as soon as possible so the contaminated water can be stored after its radioactive content is decreased.

Discharging the stored water into the sea sooner or later after confirming its safety could be a realistic option.

The most important processes in reactor decommissioning are to grasp the situation within the reactors and to extract damaged fuel. Use of robots is unavoidable in conducting work at sites that are inaccessible due to serious radioactive contamination.

The government should foster personnel in charge of decommissioning and boost assistance to develop technology that can withstand a harsh environment.

Publication Date : 08-03-2015

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