The concentration of radioactive cesium-137, which was spread about following the accident at Tokyo Electric Power Company Holdings Inc.’s Fukushima No. 1 nuclear power plant, has been rapidly decreasing in river waters in municipalities near the facility in Fukushima Prefecture, according to a survey by the Japan Atomic Energy Agency.
Compared to the speed at which the radiation of cesium-137 naturally decreases, the concentration in the rivers is decreasing at a speed tantamount to 10 times that, said the JAEA, a national agency for research and development.
The JAEA assesses that cesium on top of the ground is carried into rivers by rain but as the radioactive substance seeps underground, among other possible factors, the volume flowing into rivers might have decreased.
Following the March 2011 nuclear accident, radioactive materials were dispersed and fell onto the earth. Among these materials was cesium-137, which has a relatively long half-life of about 30 years and is releasing radiation even now.
From April 2015 to March 2018, the agency examined two rivers in the prefecture — the Ukedogawa river in Namie and the Otagawa river in Minamisoma. It sampled the waters in a 20-kilometer area around the nuclear power plant and precisely measured the concentration of cesium-137 in them.
Results showed the concentration in the Ukedogawa river was around 0.2 becquerels per liter at the start of the study, but had dropped to around 0.1 becquerels in March 2018, indicating the concentration was decreasing 10 times faster than normal. The Otagawa river also showed a similar trend, according to the agency.
Takahiro Nakanishi, a senior researcher at the JAEA, said, “If the concentration in river waters relied on for agricultural purpose decreases, the result could help local people resume their agricultural activities.”Speech