Decommissioning progress

13 Mars 2018

March 11, 2018

Decommissioning Fukushima reactors will take time but progress continues

https://mainichi.jp/english/articles/20180310/p2a/00m/0na/018000c#cxrecs_s

In this July 27, 2017 file photo, contaminated water storage tanks are seen on the Fukushima No. 1 nuclear plant grounds, in Okuma, Fukushima Prefecture. (Mainichi)

Over the past year, clumps appearing to be melted fuel debris have been found inside three reactors at Tokyo Electric Power Co. (TEPCO)'s Fukushima No. 1 Nuclear Power Plant -- which will soon mark seven years since being struck by disaster, on March 11.

However, the specific properties of the fuel debris remain unclear, and the decision on how to go about extracting the material has been delayed. The mammoth task of decommissioning the nuclear power plant, which is expected to take 40 years, is moving at a sluggish pace.

Removing the debris is the most difficult part of the decommissioning process. During an internal probe of nuclear containment vessels at the site, which involved robots, debris-like clumps were discovered in the No. 2 and No. 3 reactors, and sand-like sediment was found spread across the bottom of the No. 1 reactor. However, the specific properties and distribution of the debris has not yet been ascertained.

In September 2017, the government and TEPCO re-examined its decommissioning operation schedule. Initially, it was planned that the reactor which would undergo decommissioning first, as well as the method, would be decided by the end of the first half of fiscal 2018. However, the decision was delayed until the end of fiscal 2019 due to a lack of information concerning the situation inside the reactors, as well as the debris.

Meanwhile, as part of countermeasures against contaminated water, an ice wall designed to block the flow of underground water has almost been completed. In addition, a sub-drain well that pumps away subterranean water has been reinforced. As a result, the volume of underground water flowing into the buildings housing the reactors has been reduced from roughly 400 metric tons per day, which was the figure immediately after the outbreak of the disaster, to about 80 tons per day -- indicating that there has been some progress regarding the "entrance" policy designed to reduce the volume of contaminated water generated at the site.

However, the "exit" policy, designed to dispose of treated water after most of the radioactive materials have been removed from the contaminated water, is still up in the air. The major issue concerning this policy is that the radioactive material tritium (tritiated hydrogen) cannot be removed, in principle, from treated water.

Tritium is something that appears in the natural world. Based on the fact that it has been flowing out into the sea from nuclear facilities across the globe, the Nuclear Regulation Authority stresses that Fukushima's treated water containing tritium should be diluted and flushed out into the sea. However, due to fears that this could damage the reputation of the local fishing industry, the government and TEPCO continue to keep the treated water stored in tanks.

As a result, the amount of radioactive water stored at the site, including the treated water, has risen to about 1.05 million tons, and the number of tanks has increased to roughly 850. The government has set up a committee looking into how to dispose of the treated water, but consensus has not yet been reached.

Meanwhile, with regard to the extraction of fuel from pools of spent nuclear fuel, removal is planned from the No. 1 and No. 2 reactors in fiscal 2023, three years later than initially scheduled, and from the No. 3 reactor sometime around mid-FY2018. Special cranes are being installed to prepare for the job.