Airborne radioactive
materials released during debris-clearing work at the Fukushima No. 1
nuclear power plant were found in a town 60 kilometers away on seven
occasions since March 25.
Led by Teruyuki
Nakajima, a professor of atmospheric physics at the University of
Tokyo’s Atmosphere and Ocean Research Institute, the team noted a
surge in concentration of airborne radioactive cesium during clean-up
activities that reached the town of Marumori in neighboring Miyagi
Prefecture.
The researchers said
the findings show that radioactive materials were repeatedly released
into the environment and reached extensive areas during
debris-clearing operations.
They called on Tokyo
Electric Power Co., the operator of the Fukushima plant, to take more
care to prevent the spread of radioactive materials during
debris-clearing operations, even if it requires implementing more
costly methods.
In conducting its
research, the team placed a device to collect airborne dust at the
town office of Marumori, 59 kilometers north-northwest of the
stricken Fukushima plant. The device collected the samples at four-
or five-day intervals between December 2011 and July 2014.
The team determined
that there were eight cases in which the amount of radioactive cesium
in the samples were at least 10 times higher than normal levels and
the material likely originated from the Fukushima plant because of
wind direction and speed.
The highest level of
contamination was recorded in a sample collected between July 15 to 18, last month, reaching 50 to 100 times higher than normal levels.
TEPCO began
large-scale debris-clearing work at the plant on July 15.
Previous research by the farm ministry and Kyoto University also
showed that radioactive dust released during the work reached
locations 27 km and 48 km from the plant.
In seven other
cases, the amount of radioactive materials in the samples was about
10 times higher than normal. The research team reported the results
of its findings to the farm ministry in May.
According to TEPCO,
seven of the eight cases were recorded during the same period when
the utility was doing debris-clearing work at the No. 3 reactor
building.
The remaining case
involved samples collected between Nov. 16-20, 2012, coinciding with
an accidental water leak from a vent pipe of a cesium-absorption
device at the plant.
A TEPCO official
said it was unlikely that the accident caused a major release of
radioactive materials like the August 2013 incident.
The utility had
planned to dismantle a shroud over the No. 1 reactor building this
month to start full-scale debris-clearing work around the reactor,
but postponed the plan in order to strengthen measures to prevent the
spread of radioactive materials during clean-up activities.
A worker at the
Fukushima plant said that TEPCO has not discussed any drastic
measures, such as covering the reactor with a container.
“It will likely
resume debris cleanup when criticism calms down,” the worker said.
Asahi
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