IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
IV.A.2. Radiation Stable Resins for the Recovery of
Actinides and Palladium
The purification and
concentration of plutonium
from dilute process solutions
are major steps in nuclear spent
fuel reprocessing in current
PUREX plants. Due to its
simplicity, ion exchange
processes have advantages
over the other separation
methods for the concentration
and purification of plutonium.
Anion exchange process is
being commonly used by most
of the nuclear plants and
laboratories for plutonium
processing and purifications.
The inability of several elements
to form the anionic complexes
in nitric acid solution makes it
possible to get a better
decontamination factor. The
conventional anion exchange
resins have a styrene-DVB
based coplymers matrix.
In India, the purification and
concentration of plutonium is
carried out by conventional
anion exchange. The two major
problems which have been
encountered during plutonium
purification using the anionexchange
process are
i) very slow sorption and
desorption kinetics,
ii) radiation degradation of
the anion-exchange resin in
intense radiationfield.
The use of resin beads with
high porosity and lower bead
size is preferred to overcome
the slow kinetics. The
combination of hostile
conditions such as high
radiation and concentrated
nitric acid can degrade the
resins and various accidents
had been reported during the
anion-exchange process of
plutonium purification. Thus,
anion-exchange resins, which
possess high radiation and
chemical stability, are preferred
for the purification of
plutonium. From the literature it
is found that pyridine-based ion
exchangers have the highest
order of radiation stability. This
is because vinylpyridine resins
are less susceptible to
electrophilic attack than the
styrene-based resins. At the
centre, a programme has been
initiated to synthesise and
develop gel-type 4-
vinylpyridine(PVP) resins for
plutonium processing and
precious metal recovery. The
PVP resins were synthesized by
suspension polymerization
technique and after that resin
was methylated with
iodomethane. Three different
cross-linked (4, 8, and 12%)
gel-type 4-vinylpyridine resins
were characterized, and
evaluated for processing and
purification of plutonium and
palladium from nitric acid
medium. For palladium
recovery PVP resin was used as
it is and for plutonium
methylated resin was used. The
results were compared with
those obtained with the
conventional anion-exchange
resin namely, Dowex 1X4,
which has been studied
extensively.
Variation of DPu(IV) as a
function of acidity
From Fig.1 its is seen that
D Pu(IV) value of 4% cross-linked
PVP resin is lowest at all
acidities and for 8% the D Pu(IV) is
highest. In Dowex 1x4, the
maximum D Pu(IV) value is
attained at 7 - 8 M, whereas for
PVP resins, the maximum shifts
towards 8 - 10 M nitric acid.
The D Pu(IV) for 8% and 12%
crosslinked resins is high as
compared to Dowex 1X4.
Elution studies
The column performance of
PVP resins was compared with
that of Dowex 1X4 under
similar conditions. Pu(IV) was
loaded from 8 M nitric acid and
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