IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
IV.C.4. Glass-ceramic Waste Form for the High-level Waste
from Pyrometallurgical Reprocessing of Nuclear Fuels
The high-level radioactive
waste (HLW) generated from
pyrometallurgical reprocessing
of irradiated nuclear fuels in
molten LiCl-KCl media cannot
be immobilized in the
conventional borosilicate glass,
as chlorides have very poor
solubility in glass.
Immobilization of the chloride
waste in a glass-ceramic such
as glass-bonded sodalite, has
emerged as a promising option.
Sodalite is a naturally occurring
mineral, and the glass-ceramic
waste form based on it is
considered suitable for disposal
in geological repositories. The
waste form fabrication involves
the occlusion and/or ion
exchange of the radioactive
waste on to a zeolite, tailoring
with a glass binder, and
subsequent conversion to the
glass-ceramic. The preparation
and characterization of such a
waste form using a simulated
waste composition have been
investigated.
Dehydrated Zeolite 4A was
homogenized with simulated
chloride HLW of a
representative reference
composition (2 wt% CsCl, 2
wt% BaCl 2 , 9 wt% NdCl 3 and
the rest LiCl - KCl eutectic) in
an inert atmosphere glove box,
and the mixture was
equilibrated at 848 K for 100h
in static argon. The salt-loaded
zeolite (SLZ) was washed with
water, and the eluate analyzed
by atomic absorption
spectrometry in order to
ascertain the extent of salt
uptake in the zeolite matrix. The
SLZ was then converted to
glass-bonded sodalite
[Na 8 (AlSiO 4 )6Cl 2 ] by blending
it with 25wt % of a specially
prepared boroaluminosilicate
glass, pelletizing and heating at
1188 K for 15h in flowing
argon. By this procedure,
several batches were prepared
by varying experimental
S
N
N
S
N
N
S
N
parameters such as the zeoliteto-salt
ratio. X-ray
diffractograms of the final
waste form showed sodalite as
the major phase and nepheline
as a minor phase (Fig.1). SEM
micrograph of the product
showed a uniform
microstructure (Fig. 2).
Thermophysical properties
like thermal expansion and
glass transition temperature of
the glass-ceramic were studied
by high-temperature XRD and
differential
scanning
calorimetry, respectively. The
variation of the lattice
parameter with temperature
was found to be similar to that
S
2Theta Cu K α
S : Sodalite
N : Nepheline
Fig.1 Powder XRD pattern of the glass-bonded sodalite
N
FUEL CYCLE 109