TOKYO, October 21 (Itar-Tass) - Radioactive strontium-90 has been detected in rainwater that spilled over the protective barriers around storage tanks with contaminated fluid at Japan’s crippled Fukushima Daiichi (Fukushima 1) nuclear power plant, the NPP operator - Tokyo Electric Power Company (TEPCO) reported on Monday.
According to the company, strontium-90 in water that had accumulated due to heavy rainfall was above the limit of 10 becquerels per liter around six clusters of tanks, with the reading in one of the areas reaching 710 becquerels.
TEPCO said some of the toxic water has seeped into the ground, but that it is unlikely to have flown into the adjacent Pacific Ocean because of mounds created outside the barriers to prevent water from entering drainage channels.
How radioactive water leaks
The barriers, about 30 centimeters high, have been created to block water from spreading outside when a leak occurs in the tanks, which hold highly radioactive water. Such barriers exist around each of the 23 clusters of tanks, the Kyodo news agency reported.
When rainwater accumulates inside, TEPCO transfers it to other containers and checks its radiation level before discharging it. But the rainfall on Sunday was so heavy that water overflowed from the barriers. TEPCO said Sunday that water near a total of 12 clusters had spilled from the barriers, but it corrected the number to 11 on Monday.
Level of hazard
The Nuclear Regulation Authority has told TEPCO it will authorize the Fukushima plant to discharge water from within the barriers only if radiation readings are below 15 becquerels per liter for cesium-134, below 25 becquerels per liter for cesium-137, and below 10 becquerels per liter for strontium-90 and if other radioactive substances that emit gamma rays are not present. The legal limit for the release of strontium-90 into the sea outside the plant, meanwhile, is set at 30 becquerels per liter. Strontium tends to accumulate in bones and is feared to cause bone cancer and leukemia.
Since the beginning of October, several incidents with rainwater have occurred at the Fukushima 1 NPP. In early October, about 0.5 tonnes of radioactive water spilled over the barrier. Meanwhile, on Wednesday, due to heavy rain caused by Typhoon Wipha, the NPP reservoirs for rainwater leaked. So, the plant’s employees had to discharge the fluid into the ground