TEPCO has discovered high levels of radioactive tritium in groundwater between units 1 and 2 of the Fukushima Daiichi site; one measurement taken on 24 May was 500,000 Bq/L.
TEPCO says that there is a high possibility that tritium remaining in soil was transferred to groundwater when contaminated water leaked into the unit 2 screen pump room at unit 2 in 2011.
When water leaked into the unit 2 screen pump room, it passed through crushed rock under a power cable conduit, from where it likely spread out into the ground. Unlike caesium, which is generally absorbed into the soil, tritium has been moved by groundwater.
After past leakages of contaminated water, trenches on the site have been blocked.
The measurements are an order of magnitude greater than previous measurements in December 2012, so TEPCO reasons that groundwater has been relatively uncontaminated until now.
To halt the spread of contamination, TEPCO plans to use chemical grouting to prevent the contamination reaching the seawall, and will fill the crushed rock layer of the cable duct foundation. It also plans to monitor the area more closely.
Picture: Near Fukushima Daiichi unit 2 seawater intake, 1 April 2011