Summary of Decommissioning and Contaminated Water Management

Main works and steps for decommissioning

Fuel removal from Unit 4 SFP had been completed and preparatory works to remove fuel from Unit 1-3 SFP and fuel debris ^{(Note 1)} removal are ongoing.

Toward fuel removal from pool

Installation of a cover for fuel removal at Unit 3
Installation of the west-side stopper (February 7, 2017)

Toward fuel removal from Unit 3 SFP, works to install the cover are underway.
As measures to reduce the dose on the Reactor Building operating floor, decontamination and installation of shields were completed in June and December 2016 respectively.
Installation of a cover for fuel removal started from January 2017.

Three principles behind contaminated water countermeasures

Countermeasures for contaminated water are implemented in accordance with the following three principles:

1. Eliminate contamination sources

① Multi-nuclide removal equipment, etc.
② Remove contaminated water in the trench ^{(Note 3)}

2. Isolate water from contamination

③ Pump up ground water for bypassing
④ Pump up ground water near buildings
⑤ Land-side impermeable walls
⑥ Waterproof pavement

3. Prevent leakage of contaminated water

⑦ Soil improvement by sodium silicate
⑧ Sea-side impermeable walls
⑨ Increase tanks (welded-joint tanks)

(Note 3) Underground tunnel containing pipes.

Multi-nuclide removal equipment (ALPS), etc.

High-performance multi-nuclide removal equipment

This equipment removes radionuclides from the contaminated water in tanks and reduces risks.
Treatment of contaminated water (RO concentrated salt water) was completed in May 2015 via multi-nuclide removal equipment, additional multi-nuclide removal equipment installed by TEPCO (operation commenced in September 2014) and a subsidy project of the Japanese Government (operation commenced in October 2014).
Strontium-treated water from equipment other than ALPS is being re-treated in ALPS.

Land-side impermeable walls

Opening/closure of frozen pipes

Land-side impermeable walls surround the buildings and reduce groundwater inflow into the same.
Freezing started on the sea side and part of the mountain side from March 2016 and on 95% of the mountain side from June 2016. From December 2016, freezing started for two of seven unfrozen sections on the mountain side.
On the sea side, the underground temperature declined below 0℃ throughout the scope requiring freezing except the unfrozen parts under the seawater pipe trenches and the areas above groundwater level in October 2016.

Sea-side impermeable walls

Impermeable walls are being installed on the sea side of Units 1-4, to prevent the contaminated groundwater from flowing into the sea.
The installation of steel pipe sheet piles was completed in September 2015 and they were connected in October 2015. These works completed the closure of sea-side impermeable walls.