21 May (NucNet): Tokyo Electric Power Company (Tepco) today began discharging into the Pacific Ocean around 560 tonnes of groundwater collected at the crippled Fukushima-Daiichi nuclear station after the water passed stringent safety tests.
According to Japan’s Nuclear Regulatory Authority, the so-called “groundwater bypass system” means diverting the flow of naturally occurring groundwater between the hilltop behind Fukushima-Daiichi and the reactor buildings, which are close to the ocean.
The groundwater bypass, one of several strategies being used to reduce the accumulation of contaminated water at the plant, aims to intercept clean groundwater as it flows downhill toward the ocean, and reroute it safely around the facility. The water is temporarily stored to verify its quality before it is released into the ocean.
The bypass is expected to reduce the amount of groundwater flowing into the reactor building basements by a maximum of 100 tonnes a day, the NRA said in a letter to the International Atomic Energy Agency posted online.
Radioactive water has been increasing at the facility because groundwater is seeping into the basement of reactor buildings and mixing with water used to cool the three reactors that suffered meltdowns in the 2011 accident.
Tepco and the government jointly decided to begin releasing groundwater only after confirming that it passed “stringent safety tests” and receiving agreement from the Fukushima fishermen’s union.
Limits have been set for levels of radioactivity in the groundwater. The limits, which Tepco says are tighter than World Health Organisation guidelines for drinking water, state that released groundwater should contain less than one becquerel per litre of caesium-134 and caesium-137, five becquerels per litre of beta ray-emitting radioactive material such as strontium-90, and 1,500 becquerels per litre of tritium.
As part of its obligations under the agreement, Tepco said it will have the water quality monitored regularly by an independent third party using safety and environmental standards more stringent than those set by Japanese law. The company said it would suspend the bypass operation “if at any time water quality limits are exceeded”.
Tepco said the bypass will help reduce the volume of water that becomes contaminated and then needs to be cleaned and stored on site. This, in turn, is expected to reduce the burden on storage facilities by slowing the pace of contaminated water accumulation.