Fukushima Unit 1 Containment Inspection Update

Plans to inspect inside the containment structure of unit 1 at Fukushima Daiichi has again hit a series of delays. This isn’t the first inspection inside unit 1’s containment. It is the first that requires a larger air lock to introduce the robot.

Earlier in 2019 workers discovered increased radiation levels inside containment as they cut part of the inner hole for the air lock. This caused work stoppages as the cause of the radiation increase was reviewed. A specific cause for the radiation increase was not identified. In response, an additional dust monitor has been installed in the reactor well near the yellow containment cap. This set of sensors should detect any future increase in radioactivity leaking from the containment cap.

The location of the new dust monitor is identified in red below

The dust monitor was installed by cutting an unused pipe between the 4th floor and the reactor well.

The steps identified above show where they cut the pipe to insert the monitoring cables & sensors into containment.

Dust swipes were taken inside the 4th floor pipe after it was cut and on nearby surfaces where the new dust monitor was installed. Alpha radiation was found inside the pipe but not on nearby surfaces. Beta radiation & y rays were found inside the pipe and in smaller amounts in the other locations.

The current schedule for cutting the remainder of the air lock access into containment is scheduled for late November into January. Guide pipe & air lock installation is currently scheduled for mid-January. The actual containment inspection is currently scheduled for mid January to the end of January. The actual inspection should only take a few days. This wide scheduling window likely reflects the uncertainty and complexity of completing this work.

Source document:
https://www4.tepco.co.jp/decommission/information/committee/roadmap_progress/pdf/2019/d191031_08-j.pdf

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