Fukushima Trench Freezing Failures & Tactics Technical Report
Update: Added table of sea water data at the end and another TEPCO handout on the work released this week.
TEPCO admitted a few weeks ago to METI that the trench freezing operation underway for units 2 and 3 was not working. TEPCO initially provided few details but did give a detailed report to METI. Today TEPCO released some ideas for how they intend to overcome the problems but didn’t make the details of the problems readily available.
We reviewed the report from TEPCO to METI and found the causes and problems, below is an overview of the issues and what will be attempted to solve the problem.
TEPCO initially did a test run of the technology in December of 2013 in an unidentified tunnel at the plant. This proved successful. The area was frozen including inside pipes. Images of the test run can be found here.
Now as TEPCO’s actual installation is failing, they told the press it was a trickle of water. But the report to METI says otherwise.
The trenches begin at the turbine buildings for unit 2 and unit 3. The attempts to freeze the trenches are at access points near the turbine buildings.
Freezing location for unit 2, trench A is located in the above image.
Diagram of the trench junction where the freezing equipment is set up.
Orange = measuring tubes
Blue = freezing tube
Light blue circle = the packer bag. (image below shows what the packer bags look like) The packer bags are filled with cement or clay.
Side view of trench location 2A. Black lines are cable trays, blue vertical lines indicate the location of the freezing pipes. Horizontal light blue lines indicate the range of the height of standing water in the trench.
Trench 2A wall temperature chart. Over three dates temp readings were taken with green areas being the warmest. The charts show how much of the wall is above the temperature needed to freeze.
Location of trench 2B on the side of the unit 2 turbine building.
Diagram of the unit 2 trench 2B freezing location. Blue dots are freezing pipes, Light blue circles are packers and green dots are temperature sensors.
Unit 2 trench 2b side view. Blue vertical lines are freezing pipes, black lines are cable trays, light blue lines are water levels.
Unit 2 trench 2B wall temperatures. The location has seen some freezing over the last month but large portions seen in green are still above freezing.
Unit 3 trench A:
Location of unit 3 trench A near the unit 3 turbine building.
Unit 3 trench A location of frozen wall in the trench. Blue is frozen pipes, light blue are packers, green are temperature sensors.
Unit 3 trench A side view. Blue vertical lines are freezing tubes, light blue horizontal lines are the water level range. Work is still underway to complete this installation.
Unit 3 trench D:
Unit 3 trench D location. Blue is the location of freezing pipes, light blue are packers, green are sensors.
Unit 3 trench D side view. Blue vertical lines frozen pipes, light blue horizontal lines are the water level range.
This location is still being installed.
TEPCO inserted a scope camera via an access hole to look into these locations to understand the condition of the frozen walls.
The camera results confirmed the temperature issues:
Frozen wall 2A shows limited freezing in blue.
For frozen wall 2A they also checked the flow direction and velocity of the water moving in the trench at different heights.
TEPCO released the timeline below as their work schedule for this effort:
Some of TEPCO’s fix attempts will include throwing sandbags into certain areas, adding more freezing pipes and adding ice to the standing water in an attempt to cool it down enough to freeze the wall. Concrete is also being considered to block the tunnels. TEPCO posted a press release outlining this on July 24, 2014.
TEPCO did announce on July 24, 2014 that they have begun dumping ice into the trench in an effort to lower temperatures enough for the frozen wall to work. Once they are able to freeze these trench locations work will begin to pump out the highly contaminated water. That is expected to take about 4 months once it begins. The NRA plans to check the process of these frozen walls inside the trenches about mid-August.
Workers begin adding ice into the trench of contaminated water to try to lower the temperature near the frozen wall.
This section of work is required to make the over all frozen wall plan work and also to be able to remove the highly contaminated water from unit 2 where it has been sitting and leaking since 2011.
TEPCO released this chart explaining the contamination and some of the chemistry of the water:
All diagrams included here are courtesy of TEPCO from this report to METI
A rough English machine translation of the document can be found here.
TEPCO released a very abbreviated handout in English explaining their efforts to solve the problem
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