The Subdrain System And The Seaside Impermeable Wall: Facilities to Achieve Further Water Control at Fukushima Daiichi
FUKUSHIMA, August 13, 2014?Facilities of the two important systems that will significantly improve water management at the Fukushima Daiichi Nuclear Power Station, the seaside impermeable wall and the subdrain system, are ready for approval from the regulator and the other important stakeholders, Tokyo Electric Power Company announced.
Of the three large water management strategies, "Contaminant removal", "Contaminant isolation", "Leakage prevention", the two systems are designed to fundamentally address the latter two strategies. The subdrain system is now restored and rebuilt to greatly reduce the amount of contaminated water that currently accumulates at the reactor facilities at the site each day, one of the most important measures to address "Contaminant isolation".
The seaside impermeable wall is installed to prevent groundwater from flowing out to the sea, a measure that aims to address "Leakage prevention".
The two systems also aim to further control and reduce the amount of radioactive material released from the site, TEPCO explained.
"These two systems are important components of our larger strategy to improve water management at Fukushima," said Naohiro Masuda, TEPCO's Chief Decommissioning Officer. "Along with the other multi-layered measures which includes sophisticated water treatment systems ("Contaminant removal"), groundwater bypass system and development of the ‘ice wall' around the perimeter of the four reactor units ("Contaminant isolation"), I believe the two systems will contribute to further improving water management at the site."
The subdrain system had to be restored and rebuilt after it was damaged in the March 2011 accident following the earthquake and tsunami. Once back in operation, the subdrain system will capture 500 to 700 tons per day of underground water enabling it to be pumped up so that it can be treated.
The water will be treated in a purification system that will clean the water to a safer level than any international or Japanese safety standard. TEPCO has assured all concerned that any water discharged would meet the same stringent criteria, and be subject to the same monitoring requirements, as the water currently being discharged as part of the "groundwater bypass" system. No final decision has been made concerning the ultimate disposition of the water, and no discharge will be made without the agreement of the relevant governments and local fishermen, the company said.
As a result of this strategy, the total daily accumulation of water is expected to be consequently cut by approximately 200 tons per day.
Seaside Impermeable Wall
The seaside impermeable wall is a steel pipe sheet pile wall being constructed on the east side of the facility, to prevent groundwater that might otherwise continue to flow eastward (and downhill) into the sea, from flowing out.
This groundwater has not entered the reactor buildings and is therefore not nearly as contaminated as the water that has collected in those basements. However some of this natural groundwater may have come into contact with minor contamination already in the ground from the 2011 accident. Together with the subdrain system which pumps up upstream groundwater, the seaside impermeable wall will finally prevent the groundwater from flowing out to the sea. Groundwater collected at the wall will be treated, along with the water collected from the subdrain system.
Together, the two systems will further control and reduce radioactive material which goes out to the ocean, such as Strontium 90 and Cesium 137 will be reduced to one-fortieth, the company explained.
For details, please go to http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2014/images/handouts_140811_03-e.pdf and http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2014/images/handouts_140811_04-e.pdf
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