After the accident, highly contaminated water accumulated inside the seawater piping trench, an underground tunnel originally for storing pipes and cables, on the ocean side of the Unit 2 to Unit 4 turbine buildings. This contaminated water was removed from the trench by transferring it to the turbine buildings or elsewhere, considering the nature of the contamination and the quality and volumes of water. The trench was then filled by suitable methods, selecting filling materials in consideration of the structure and other factors, to mitigate leakage risks.

Overview of Seawater Piping Trench

Overall Diagram of Seawater Piping Trench

Overall Diagram of Seawater Piping Trench

Cross-Section of Seawater Piping Trench

Cross-Section of Seawater Piping Trench

Status of Seawater Piping Trench

Overall progress in contaminated water removal as of March 2017: 100%

Unit 2 Unit 3 Unit 4
Status
  • Filling of tunnel portion: Completed December 18, 2014
  • Filling of vertical shafts: Completed March 9, 2017
  • Transfer of water accumulated in trench: Completed June 30, 2015
  • Filling of tunnel portion: Completed April 8, 2015
  • Filling of vertical shafts: Completed August 27, 2015 (except for upper part of shaft D)
  • Transfer of water accumulated in trench: Completed July 30, 2015
  • Filling of tunnel portion: Completed March 21, 2015
  • Filling of openings II and III: Completed April 28, 2015
  • Transfer of water accumulated in trench: Completed December 11, 2015
  • Tunnel above water discharge channels: Completed December 21, 2015
Remaining water volume 0m3 0m3 0m3
Filling volume Approx. 4,910m3 Approx. 5,980m3 Approx. 780m3

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