11 Mar (NucNet): Contaminated rainwater has been found seeping into the ground in the Fukushima-Daiichi nuclear power station’s water storage tank area, operator Tokyo Electric Power Company (Tepco) has said.
Tepco told the Japan Nuclear Regulatory Authority (NRA) today that approximately 750 metric tonnes of rainwater containing strontium-90 (Sr-90) “may have leaked” from tanks storing contaminated water used for cooling the damaged reactors.
Tepco said the water is “unlikely” to leak into the ocean through any of the drainage channels, but it is monitoring the situation.
According to reports, there has been heavy rain in Fukushima prefecture and rainwater had accumulated in the water storage tank area.
The water storage tanks have an inner dyke to protect the tank area and an outer dyke to prevent the possible spread of any leakage from the inner dyke. Tepco said “it was possible that some water may have seeped out” through some of the protective sealing designed to contain water inside the inner dyke.
Analysis of the water collected from the outer dyke showed total beta-radiation levels – the total amount of beta-emitting radionuclides such as Sr-90 – ranged from 150 to 8,300 becquerels per litre (Bq/ℓ). Caesium levels were not detected.
Tepco’s limits for groundwater contamination say that groundwater should contain less than 5 Bq/ℓ of beta ray-emitting radioactive material and 1 Bq/ℓ of caesium-134 and caesium-137.
Tepco said it will continue to investigate the cause of the rainwater contamination and will take steps to further waterproof the outer dyke.
On 9 March 2015, the NRA said one of the key issues remaining at Fukushima-Daiichi is dealing with contaminated water that is being stored on-site after being used to cool the reactors.
Tepco said it had started using a new high-performance system for treatment of the contaminated water. The new system reduces radioactive Sr-90 to non-detectable levels, which will reduce any risk in the event of a leak, lessen offsite radiation doses, and decrease the amount of radiation exposure of workers on patrol, Tepco said.
