Ground water contamination has been rising steadily at the Daiichi site, especially since the summer of 2013 when water from the well between the ocean and unit 1 measuring a record 5 million Becquerels per liter of radioactive Strontium-90 alone in July 2013 (“Record Strontium-90 Level,” 2014).
The quantity of Strontium-90 in the July 2013 well water was 170,000 times the permissible level. TEPCO stated the total Becquerels per liter was likely 10 million when all beta ray sources are included (“TEPCO to Review,” 2014).
TEPCO had originally interpreted the July 2013 beta tests as indicating 700,000 Becquerel per liter of Strontium-90, but revised the figure upwards to 5 million in February of 2014. Critics charged that TEPCO was hiding data after the company announced it would not revise known inaccuracies in data reported from July 2013 through December 2013 (“TEPCO Withheld,” 2014).
The results that had been reported by TEPCO during this period and after indicated a clear upward trend in strontium, tritium and cesium contamination levels from July 2013 forward (“TEPCO Announced,” 2014).[i]
January 27 2015 TEPCO measured 31,000,000 Bq/m3 of Strontium-90 in boring well nearest Reactor 2, a level which was more than 10 percent more than reported in December of 2014 (Fukushima Diary 1/32/2015 http://fukushima-diary.com/2015/01/31000000-bqm3-strontium-90-measured-nearest-boring-well-reactor-2; TEPCO).
By February of 2015 TEPCO was reporting even higher levels of Strontium-90 in the same location, with the highest sample measured at 590,000,000 Bq/m3 of Strontium-90 (Fukushima Diary 590,000,000 Bq/m3 of Strontium-90 measured from groundwater of Reactor 2 seaside). The spiking strontium levels are consistent with the predictions of the German melt-through scenario. Highly contaminated ground water that may be flowing out to sea. For example, TEPCO identified a surge in contaminated ground water as a likely cause for a recorded spike in beta readings to 7,230,000 Bq/m3 in drain water flowing from the Daiichi plant directly into the ocean (Fukushima Diary 2/22/2015, “7230,000 Bq/m3”).
The “German Risk Study, Phase B” found that a core meltdown accident could result in complete failures of all structural containment, causing melted fuel to exit the reactor foundation within five days (cited in Bayer, Tromm, & Al-Omari 1989).
Moreover, the study found that even in the event of an intact building foundation, passing groundwater would be in direct contact with fuel, causing leaching of fission products. Strontium leaches slower than cesium. A follow-up German study, “Dispersion of Radionuclides and Radiation Exposure after Leaching by Groundwater of a Solidified Core-Concrete Melt,” predicted that strontium contamination levels would rise exponentially years after a full melt-through located adjacent to a river (Bayer, Tromm, & Al-Omari, 1989).
The study’s experimental conditions are roughly similar to Daiichi’s site conditions, including groundwater emptying into an adjacent river, whereas Daiichi is physically situated above an underground river emptying into the sea.
The study predicted concentrations of Strontium-90 in river water would spike relatively suddenly, but maintain extraordinarily high levels of contamination for years: “The highest radionuclide concentration of approx. 1010 Bq/m3 is reached by Sr-90 after some 5000 days.”