TEPCO's rubble removal at Fukushima plant likely spread cesium to rice paddies
Tokyo Electric Power Co. plans to clear debris from the Fukushima No. 1 nuclear plant despite strong indications that earlier removal work contaminated rice paddies far from the stricken facility, The Asahi Shimbun has learned.
The agriculture ministry pointed out the possibility that the removal of rubble from the plant site in August last year spread radioactive substances to 14 rice paddies in Minami-Soma outside the evacuation zone and more than 20 kilometers from the plant.
Cesium levels in the rice crops harvested last autumn exceeded the safety standard of 100 becquerels per kilogram, according to ministry officials.
Radioactivity readings above the standard were also detected from rice grown at five locations inside the evacuation zone.
The ministry called on TEPCO to take preventive measures in its debris-removal work.
Although the utility has since suspended its clearing operations at the plant, the company plans to soon dismantle a cover installed on the No. 1 reactor building, where highly contaminated debris remains to be removed.
TEPCO has not told the public about the ministry’s findings.
“(If TEPCO hopes to resume rubble-clearing operations), providing information on the possibility of the spread of (contaminated substances) is a major premise,” said Takehiko Murayama, a risk management professor at the Tokyo Institute of Technology.
An agriculture ministry survey found that some parts of rice crops that emerged in mid-August were contaminated. If the crops had drawn up radioactive substances released into the soil immediately after the Fukushima nuclear plant was hit by the Great East Japan Earthquake and tsunami in March 2011, those substances would be detected uniformly throughout the plants.
Since they weren’t, the ministry concluded that the radioactive substances had been newly released at least by the end of September 2013, the harvest period for the rice crops.
The ministry is pointing to Aug. 19, when TEPCO removed a large piece of wreckage from the plant’s No. 3 reactor building. Radioactive dust under the debris blew away in the process and exposed two workers away from the reactor to radiation.
A maximum reading of 13 becquerels per square centimeter was detected from the heads of the two workers. Air dose rates increased at five measuring points 2.8 to 8.3 km north-northwest on the leeward side of the nuclear plant.
The Fukushima prefectural government attributed the increase in air dose rates to radioactive substances released during the Aug. 19 removal operation.
“We cannot think of any other factors,” said a prefectural official. “It is almost certain that the rise in readings was caused by the clearance work.”
The farm ministry also said Minami-Soma lies downwind of the five measuring spots, and that the System for Prediction of Environmental Emergency Dose Information (SPEEDI) estimated that the released particles would reach the city within three hours.
It also says Minami-Soma is the only city with more than one site contaminated with cesium levels exceeding the safety standard, and that the high readings were not detected from rice crops in the area the previous fiscal year.
Ministry officials said they planned to disclose the findings after confirming the cause of the rice crop contamination.
TEPCO said it will resume debris-clearing efforts at the nuclear plant while taking preventive measures based on the ministry’s instructions that came in March this year.
However, the utility said it has yet to learn how far the released particles spread.
The company said its plans to dismantle the cover on the No. 1 reactor building will be the fastest way to remove wreckage from the site. TEPCO will also spray more anti-scattering agents than usual during the operation.
But the company acknowledged that the procedure will still lead to the release of a large amount of radioactive substances, and the spread of the substances will depend on the weather and the wind direction.