Universitat Autònoma de Barcelona
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Scientists from the Universitat Autònoma de Barcelona (UAB)
investigated the levels of radioactive strontium and cesium in the coast off
Japan in September 2013.
Radioactive levels in seawater were 10 to 100 times
higher than before the nuclear accident, particularly near the facility,
suggesting that water containing strontium and cesium isotopes was still
leaking into the Pacific Ocean.
March
11 will be the 5th anniversary since the nuclear accident in Fukushima, Japan.
The Tohoku earthquake and the series of tsunamis damaged the Fukushima Dai-ichi
Nuclear Power Plant (FDNPP) causing a massive release of radioactivity into the
atmosphere and the Pacific Ocean.
Since then, the Tokyo Electric Power Company (TEPCO) and the Japanese authorities have focused on controlling the water flowing in and out of the FDNPP and on decontaminating the highly radioactive water used as coolant for the damaged reactors (about 300 m3 a day, cubic meter = 1000 L). This cooling water is then stored in tanks and, to some extent, being decontaminated.
A
new study recently published in Environmental Science and Technology, uses data
on the concentrations of 90Sr and 134,137Cs in the coast off Japan from the
moment of the accident until September 2013, and puts it into a longer-time perspective
including published data and TEPCO's monitoring data available until June 2015.
This study continues the work initiated after the accident in 2011 by some of
the authors.
These and other partners from Belgium and Japan are currently
involved in the European FRAME project lead by Dr. Pere Masqué that aims at
studying the impact of recent releases from the Fukushima nuclear accident on
the marine environment.
FRAME is encompassed within the European COMET project (https://wiki.ceh.ac.uk/display/COM/COMET-FRAME).
Seawater
collected from the sea surface down to 500 m between 1 and 110 km off the FDNPP
showed concentrations up to 9, 124 and 54 Bq·m−3 for 90Sr, 137Cs and 134Cs,
respectively. The highest concentrations, found within 6 km off the FDNPP, were
approximately 9, 100 and 50 times higher, respectively, than pre-Fukushima
levels.
Before the accident, the main source of these radionuclides was
atmospheric deposition due to nuclear bomb testing performed in the 1950s and
1960s.
The presence of 134Cs (undetectable before the accident) and the
distinct relationship between 90Sr and 137Cs in the samples suggested that
FDNPP was leaking 90Sr at a rate of 2,3 -- 8,5 GBq d-1 (giga-Becquerel per day)
into the Pacific Ocean in September 2013.
Such a leak would be 100-1000 times
larger than the amount of 90Sr transported by rivers from land to ocean.
Additional risk is related to the large amounts of water stored in tanks that
have frequently leaked in the past.
These results are in agreement with TEPCO's
monitoring data which show levels of 90Sr and 137Cs up to 10 and 1000 times
higher than pre-Fukushima near the discharge channels of the FDNPP until June
2015 (most recent data included in the study).
The presence of 90Sr and
134,137Cs in significant amounts until 2015 suggests the need of a continuous
monitoring of artificial radionuclides in the Pacific Ocean.
