Particulate plutonium released from the Fukushima Daiichi meltdowns


Date:
July 14, 2020
Source:
University of Helsinki
Summary:
Small amounts of plutonium (Pu) were released from the damaged
Fukushima Daiichi Nuclear Power Plant (FDNPP) reactors into the
environment during the site's 2011 nuclear disaster. However,
the physical, chemical, and isotopic form of the released Pu has
remained unknown. Now, recent work has shown that Pu was included
inside cesium-rich microparticles (CsMPs) that were emitted from
the site.



FULL STORY ========================================================================== Small amounts of plutonium (Pu) were released from the damaged Fukushima Daiichi Nuclear Power Plant (FDNPP) reactors into the environment during
the site's 2011 nuclear disaster. However, the physical, chemical,
and isotopic form of the released Pu has remained unknown.


==========================================================================
Now, recent work published in the journal Science of the Total Environment
has shown that Pu was included inside cesium-rich microparticles (CsMPs)
that were emitted from the site. CsMPs are microscopic radioactive
particles that formed inside the Fukushima reactors when the melting
nuclear fuel interacted with the reactor's structural concrete. Due to
loss of containment in the reactors, the particles were released into
the atmosphere; many were then deposited across Japan.

Studies have shown that the CsMPs are incredibly radioactive and that
they are primarily composed of glass (with silica from the concrete) and radio-cesium (a volatile fission product formed in the reactors). Whilst
the environmental impact and distribution of the CsMPs is still an active subject of debate, learning about the chemical composition of the CsMPs
has been shown to offer a much-needed insight into the nature and extent
of the FDNPP meltdowns.

The study published in Science of the Total Environment, involving
scientists from Japan, Finland, France, Switzerland, the UK, and USA,
was led by Dr.

Satoshi Utsunomiya and graduate student Eitaro Kurihara (Department of Chemistry, Kyushu University). The team used a combination of advanced analytical techniques (synchrotron-based micro-X-ray analysis, secondary
ion mass spectrometry, and high-resolution transmission electron
microscopy) to find and characterize the Pu that was present in the
CsMP samples.

The researchers initially discovered incredibly small uranium-dioxide inclusions, of less than 10 nanometers in diameter, inside the
CsMPs; this indicated possible inclusion of nuclear fuel inside the
particles. Detailed analysis then revealed, for the first-time, that
Pu-oxide concentrates were associated with the uranium, and that the
isotopic composition of the U and Pu matched that calculated for the
FDNPP irradiated fuel inventory.

Dr Utsunomiya stated "these results strongly suggest that the nano-scale heterogeneity that is common in normal nuclear fuels is still present in
the fuel debris that remains inside the site's damaged reactors. This
is important information as it tells us about the extent / severity of
the melt-down.

Further, this is important information for the eventual decommissioning
of the damaged reactors and the long-term management of their wastes."
With regards environmental impact, Dr Utsunomiya states "that as we
already know that the CsMPs were distributed over a wide region in
Japan (up to 230 km from the FDNPP), small amounts of Pu were likely
dispersed in the same way." Professor Gareth Law, a co-author on
the paper from the University of Helsinki, indicated that the team
"will continue to characterize and experiment with the CsMPs, in an
effort to better understand their long-term behavior and environmental
impact. It is clear that CsMPs are an important vector of radioactive contamination from nuclear accidents." Professor Bernd Grambow, a
co-author from Nantes/France, states that "while the Pu released from
the damaged reactors is low compared to that of Cs; the investigation
provides crucial information for studying the associated health impact." Professor Rod Ewing at Stanford University emphasized that "the study used
an extraordinary array of analytical techniques in order to complete
the description of the particles at the atomic-scale. This is the
type of information required to describe the mobility of plutonium in
the environment." Utsunomiya concluded "It took a long time to publish
results on particulate Pu from Fukushima. I would like to emphasize that
this is a great achievement of international collaboration. It's been
almost ten years since the nuclear disaster at Fukushima," he continued
"but research on Fukushima's environmental impact and its decommissioning
are a long way from being over."

========================================================================== Story Source: Materials provided by University_of_Helsinki. Original
written by Gareth Law.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Eitaro Kurihara, Masato Takehara, Mizuki Suetake, Ryohei Ikehara,
Tatsuki
Komiya, Kazuya Morooka, Ryu Takami, Shinya Yamasaki, Toshihiko
Ohnuki, Kenji Horie, Mami Takehara, Gareth T.W. Law, William Bower,
J. Frederick W. Mosselmans, Peter Warnicke, Bernd Grambow, Rodney
C. Ewing, Satoshi Utsunomiya. Particulate plutonium released from
the Fukushima Daiichi meltdowns. Science of The Total Environment,
2020; 743: 140539 DOI: 10.1016/j.scitotenv.2020.140539 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200714101238.htm

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