Update: Fukushima Unit 1 & 3 Containment Leaks
New information was published by TEPCO updating details about the new containment water leaks caused by the February earthquake.
At Unit 1 they found the water level dropped then stabilized around the lower side of the vacuum breaker tubes on the suppression chamber. If the water level is low enough containment slightly loses pressure. This indicates a “gas” leak, or a route that air can escape in enough quantity to lower containment pressure. TEPCO mentioned they plan to increase water injection as needed to keep the water level within the current height range until the end of the month. This may become a permanent tactic to keep air from escaping containment.
This lower water level has caused a new problem. The upcoming containment inspection using a floating ROV unit assumed the water level in containment would be above the downcomer tubes. The ROV requires guide rings to prevent it from becoming entangled in equipment and structures inside containment. Those guide rings were to be placed on the flat covers over the downcomer tubes. Without the water level at the old height this can not be done. The temporary thermometer sensor installed in containment would now be in the way of the ROV if they attempted the inspection without the guide rings. This essentially ruins the plan for the upcoming inspection. TEPCO did not mention any immediate plan to deal with this challenge.
For unit 3, this most recent update included a diagram of the water level inside containment. This shows the water level drop and to the left the MSIV room where past and new water leaks have taken place.
The leak at unit 3 is problematic as it has increased containment leakage into the first floor areas of the reactor building. It doesn’t appear to be causing a larger reduction of the water level in containment.
Unit 1’s leak appears more problematic as it has created a new air pathway out of containment that is hard to control. The upcoming inspection that would have provided important information about the conditions inside the reactor pedestal is now in doubt.
We expect this issue will have more information forthcoming and will update as new information is made available.
TEPCO document:
https://www.tepco.co.jp/decommission/information/newsrelease/reference/pdf/2021/1h/rf_20210318_1.pdf
English translation:
https://www.dropbox.com/s/dijpynw3vvbmozy/units1_3_water_containment_drop_rf20210318_1_translated.pdf?dl=0
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