December 6, 2021
On December 6, Tokyo Electric Power Company (TEPCO) began to drive steel pipes into the ground to stop the inflow of underground water into the thawed part of the frozen soil barrier wall (about 1.5 km long) built underground around the No. 1 to No. 4 reactors at the Fukushima Daiichi Nuclear Power Plant (Okuma and Futaba towns, Fukushima Prefecture). Over the course of about a week, eight steel pipes with a diameter of 35 centimeters and a maximum length of six meters will be driven into the outside of the wall, creating a wall about four meters wide. If the water is not stopped, additional steel plates will be driven into the wall.
 According to TEPCO, the frozen soil wall is believed to be thawing at the intersection of the southwest side of Unit 4 and the underground tunnel for drainage. The temperature of the ground has been above zero since mid-September, and it has been confirmed that it has reached more than 10 degrees Celsius.
 The frost wall has been in operation since 2017 to prevent the inflow of groundwater into the reactor building, where melted nuclear fuel (debris) remains from the accident, and to reduce the generation of contaminated water. About 1,600 freezing pipes (30 meters long) driven into the ground are circulated with cooling liquid at 30 degrees below zero to freeze the surrounding soil.
https://www.tokyo-np.co.jp/article/147155?rct=national&fbclid=IwAR30nXaBUALO9eC4RHZkaRsXHg3j01jRmWd0RBkk4oF53UDmROD0Dk3YGNg