19 Jun (NucNet): Higher concentrations of the radioactive isotopes tritium and strontium-90 have been found in the groundwater below units 1 to 4 of the Fukushima-Daiichi nuclear power plant, operator Tokyo Electric Power Company (Tepco) has confirmed.
The company said levels of tritium had been detected at 0.5 million becquerels per litre (Bq/ℓ) and of strontium-90 at 1,000 Bq/ℓ.
Tepco said it is working to determine the extent of contaminated groundwater and implement measures in order to prevent the contaminated water from leaking into the ocean.
The company said: “We assume contaminated water leaked at the time of the accident and has been diffusing in nearby ground.”
Sampling of the groundwater in the area, which is near the turbine building, will continue, Tepco said.
According to Tepco, testing of groundwater outside the Unit 2 turbine building had shown that the level of strontium-90 had increased by more than 100 times between December 2012 and May 2013.
Tepco said it was likely the radioactive material entered the environment after water poured over the melted fuel in Unit 2 and leaked out via the turbine building, which is between the reactor and the ocean.
Tritium is a radioactive isotope of the element hydrogen. According to the US Environmental Protection Agency (EPA), exposure to tritium increases the risk of developing cancer.
However, because tritium emits very low energy radiation and leaves the body relatively quickly, for a given amount of activity ingested, tritium is one of the least dangerous radionuclides. According to radiation protection guidelines, a concentration of up to 7,000 Bq/ℓ would be considered acceptable for drinking water.
Strontium-90 is a long-living, biologically active radioactive isotope of strontium produced by nuclear fission with a half-life of 28.8 years.
According to the EPA, it tends to deposit in bone and blood-forming tissue and can be linked to increase risk of cancer.
According to EPA guidelines, the maximum contaminant level of strontium-90 in drinking water is 0.3 Bq/ℓ, significantly lower than the recommended level for tritium.
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