31 Jan (NucNet): Significant progress has been made to move Fukushima-Daiichi from an emergency situation to a stabilised situation but management of contaminated water remains critical to the success of decommissioning, an International Atomic Energy Agency review mission has said.
The review team urged Japan’s government to urgently decide on how to dispose of treated water containing tritium and other residual radionuclides from the nuclear station, which was shut down by an earthquake and tsunami in March 2011.
The treated water is accumulating in tanks on site and is expected to reach the currently planned tank capacity within three to four years.
The water may require further treatment to reduce radionuclides to authorised levels before any of the five disposal methods being considered by the government can be implemented. The methods are ground injection, controlled discharge into the sea, discharge as steam, discharge as hydrogen, and solidification for underground burial.
Many improvements have been recorded since a previous mission in 2015, although water management remains critical to decommissioning, the team said.
Tepco has completed the construction of a 1.5km frozen underground wall designed to block groundwater from entering the reactor buildings.
The project involved 1,568 pipes placed into the ground 30 meters deep around the four reactor buildings to circulate liquid at minus 30 degrees and freeze the soil around them. Groundwater entering the reactor buildings had been coming into contact with melted nuclear fuel and other debris from the March 2011 accident, resulting in an increasing amount of contaminated water.
The finding are contained in the final report by an IAEA team that reviewed Japan's efforts to plan and implement the decommissioning of Fukushima-Daiichi. The report is based on findings made during a 5-13 November 2018 visit to Tokyo and Fukushima-Daiichi by the 13-member team.
The report contains additional details and expands on a preliminary summary report released at the end of the mission. Both contain the same advisory points on topics including long-term radioactive waste management, measures against contaminated water, the removal of spent nuclear fuel and fuel debris, and public communications.
The report is online: https://bit.ly/2MI73LV