In a coastal area long silent due to the Fukushima nuclear accident, the only sounds of human activity on June 18 were from workers removing rubble and continuing their decontamination efforts. But soon, their supervisor discovered something that broke up the monotony of the work and added to the eeriness of the atmosphere.
After a call to the Environment Ministry, Takeshi Kato, 55, a ministry specialist, immediately headed to the location about 15 kilometers south of the crippled Fukushima No. 1 nuclear power plant.
As he slowly walked around with a dosimeter, he reached a hot spot where radiation levels nearly doubled those of the surrounding areas. Using a fallen branch to clear away dirt, Kato uncovered a grayish pile about 3 centimeters long, about 1.5 cm wide and about 0.5 cm thick.
The surface of the pile, which looked like soil, had gamma ray readings of about 85 microsieverts per hour. The total reading, including beta rays, came to 1 millisievert per hour.
It was the first of four mysterious objects with high radiation levels found near the mouth of the Idegawa river in Naraha, Fukushima Prefecture.
Officials at the government and Tokyo Electric Power Co., the plant’s operator, do not know where these objects came from or why they have high radiation levels. In fact, they are not sure what these objects actually are or were used for.
Kato thought the gray pile might have been radioactive materials used at a medical institution. That thought came to mind because of the incident in October 2011, when bottles of radium were found under the floor of an abandoned residence in Tokyo’s Setagaya Ward.
Under the special measures law to deal with pollution by radioactive materials, TEPCO is responsible for processing any waste emerging from the grounds of the Fukushima No. 1 nuclear plant. Based on the law, the Environment Ministry asked TEPCO to gather up and study the mystery pile.
TEPCO workers later checked the Naraha area and discovered the other objects with high radiation readings. All three objects were small enough to be held in one hand.
On July 2, a fluffy object that looked like tree bark was found, followed by what looked like a black plastic sheet and wood chips with no elasticity on July 5.
One hypothesis is that the objects flowed down the Idegawa river, but that theory is highly implausible because all four objects were found at least 100 meters from the river.
Another theory is that the objects were swept out to sea from the Fukushima No. 1 plant and eventually washed ashore. The coastal levee that was once located in the area was destroyed by the tsunami that followed the Great East Japan Earthquake on March 11, 2011.
“Rubble likely was blown out into the ocean by the hydrogen explosions that occurred at the Fukushima No. 1 plant,” an official with the Naraha municipal government said. “There is the possibility that lighter objects were washed back ashore.”
Rumors are circulating among local residents that the objects were reactor building pieces that were blown away in the hydrogen explosions. But no similar objects have been found in areas further north that are closer to the nuclear plant.
The area of Naraha had been designated a no-entry zone due to its proximity to the nuclear plant. No residents currently live there, but the government has designated it as a place where preparations can begin to lift the evacuation order.
Trucks continue to navigate the narrow streets as part of efforts to decontaminate the area of radioactive fallout. The gray pile was discovered during work to prepare a space for the construction of wave-dissipating blocks.
TEPCO officials are studying the four objects at the Fukushima No. 1 plant.
The gray pile appears to be made of rubber.
The fragile object that looked like part of a black plastic sheet had an extremely high radiation reading of 36 millisieverts per hour when combining beta and gamma rays, TEPCO officials said.
Its ratio of radioactive cesium-134 and -137 was close to 1:2, leading TEPCO officials to conclude that cesium generated by the Fukushima nuclear accident likely attached to the object.
However, it is still unclear where and how the objects were contaminated by radiation. A further study will be required to determine what the materials were originally used for.
Tetsuji Imanaka, assistant professor of nuclear engineering at the Kyoto University Research Reactor Institute, said reliable experts should handle the study.
“Rather than leave the investigation up to TEPCO, which has lost the public’s trust, a more appropriate agency, such as the Japan Atomic Energy Agency, should conduct a thorough investigation,” Imanaka said.
TEPCO sources said they were considering asking an outside agency to conduct a detailed analysis, citing limitations on what the utility could investigate..