Removal of radionuclides by ferrocyanide sorbents for
the treatment of liquid radioactive wastes of nuclear power plants
A.Toropov., toropov@nnc.kz
Radioactive waste management, being an integral part of the nuclear fuel
cycle, is one of the key areas in the development of nuclear energy in general. [1].
Currently, the reactor BN-350 in Aktau, Kazakhstan is being
decommissioned. The nuclear power complex in Mangistau stores about 5,000 m3
of liquid radioactive waste (LRW). This LRW has a total volume activity of 107-108
Bq L-1. The status of storage tanks is
close to the emergency. However, the LRW with its high salt content can in the long term corrode
the structural materials of these tanks, and this poses serious environmental
risks in its vicinity.
In international practice, selecting the most appropriate method for
managing LRW is determined by technical and non-technical factors. The most
frequently used techniques include micro-ultrafiltration using ceramic filters,
reverse osmosis and selective sorption on organic and inorganic materials. Is known successful method employed in the
LRW cooling pool at the Taiwan Research Reactor uses a cascade of ceramic
filters with diatomite [2].. However,
this technology cannot be applied on highly mineralized LRW, which is the LRW
in BN-350.
Also is not effective to apply the processing technologies which use of
reverse osmosis membranes due to the limitations on the chemical composition
and salinity of liquid wastes. For the processing of
concentrated
of LRW with
a high content
of nitrates and borates in
the Loviisa NPP (Finland) and the
Paks NPP (Hungary) use a deposition
technology borates as crystalline precipitation and
further purification
of the
cesium ions
with sorbents based
on cobalt ferrocyanide. Also as sorption
materials used ferrocyanides other metals
as well as their composite materials, such as copper
and nickel ferrocyanides [3].
This article have been studied composite
materials based on ferrocyanides of
metals applied on natural sorbent - mineral
matrix to make the benefits of the
sorbent in the chemical and radiation resistance, which achieved
by the combination
of qualities each
of them.
The purpose of
research was
the choice of
the most suitable composite
material based on
metal's ferrocyanide and natural
sorbent for the extraction of cesium from highly
mineralized
LRW.
For the study
of sorption properties
of the composites
have been synthesized 15 composites ferrocyanides copper,
nickel, cobalt were applied to five types
of mineral sorbents of East Kazakhstan region.
Sorption of
microquantities of cesium
on composite ferrocyanide sorbents were
carried out in
static conditions by
continuously
stirring sample of
air-dry sorbent with an aliquot of
the liquid phase
during 1 hour,
then to stand for 2 hours to an
additional capture of cesium ions sorbent particles. The ratio of the
solid and liquid
phases was 1:400. After
standing the liquid and solid phases
were separated
by filtration through
cellulose filter paper.
Contents of
the main components of salinity
and cesium were determined by
atomic emission spectrometry (ICP-AES) on
the instrument
iCAP 6300
and mass spectrometry (ICP-MS)
instrumentation by
ELAN 9000. Activity radioactive
tracers -
cesium isotopes was
determined by
gamma- spectrometers with semiconductor
detector CANBERRA. pH was
monitored by
potentiometric pH
meter Mettler Toledo. Repeated experiments – are
three-time.
This article
studied a series of
sorbents for their ability to absorption of cesium
- main dose radionuclide of LRW. Revealed that
the most effective
composite materials are ferrocyanides copper applied
on mineral sorbent. The
distribution coefficients
of unmodified natural sorbents determined
by the values
Kd = 102, ferrocyanide composite sorbents copper
and nickel Kd = 103-104. The
optimum time
of sorption purification -
1 hour. Among the factors affecting the extraction
of cesium from solutions, the
most significant effect
is the concentration of
organic matter.
The
results of the research can be seen that at pH values above 10, as the
adsorption capacity of composite sorbents and pure ferrocyanides directionally
begins to decline, and for pure ferrocyanide reduction is more noticeable. With additional studies, the most effective composite sorbents
can be tested on real LRW which the similar comrosition.
1.The Principles of Radioactive Waste Management. – Vienna: IAEA, Safety
series, ¹ 111-F, STI/PUB/989, 1995
2. Chung-Ping Huang, Tzung-Yi Lin, Ling-Huan Chiao, Hong-Bin Chen.
Characterisation of radioactive contaminants and water treatment trials for the
Taiwan Research Reactor’s spent fuel pool // Journal of Hazardous Materials –
233-234 (2012) P. 140-147
3. Milyutin V., Kononenko O., Mikheev S., GelisV. Sorption of cesium on
finely dispersed composite ferrocyanide sorbents / / Radiochemistry. - 2010. -
T.52. - ¹ 3. - P.238-240.