Jiji Press, Apr. 13, 2014: Up to one ton of radioactive water has leaked out of a plastic storage tank at […] Fukushima No. 1 nuclear plant, TEPCO said Sunday […] some 700 meters away from the shore […] While the tank’s lower part is damaged to allow tainted water to flow into the ground […] The water contained 440 becquerels [per liter] of cesium-134 and 1,200 becquerels [per liter] of cesium-137 as well as 1,400 becquerels [per liter] of beta ray-emitting radioactive substances such as strontium-90, according to TEPCO.
Kyodo, Apr. 12, 2014: August water leak at No. 1 far more toxic than announced: Tepco […] After recalculating the radiation level, Tepco said the water contained 280 million becquerels per liter of beta ray-emitting radioactive materials such as strontium-90, instead of 80 million becquerels¹. A total of 300 tons of toxic water was found to have leaked at that time, part of which is believed to have flowed into the adjacent Pacific Ocean. The Nuclear Regulation Authority assessed the severity of the incident to be level 3 on an eight-point international scale. […]
¹ 280,000,000 Bq/liter of beta ray-emitting radioactive materials such as strontium-90 * 1,000 liters/metric ton * 300 tons = 84,000,000,000,000 Bq of beta ray-emitting radioactive materials such as strontium-90
Soon after the INES level 3 incident, a Tepco release stated: “We determined that this incident corresponds to “a case when nuclear fuel material (not in the form of gas) or the like has leaked within an area controlled by the company due to an unpredictable event such as a failure of a nuclear reactor facility for power generation” as per Article 18, item 12 of the regulations concerning the operational safety and the protection of specified nuclear fuel material at the TEPCO’s Fukushima Daiichi NPS nuclear reactor facilities.”