IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
in thermoelectric peltier
element module for
maintaining temperature of
sample. Samples were loaded
in polystyrene cups and placed
into the activity meter. The
activity meter was standardized
using a two-step procedure. In
the first step, purified and
degassed ASTM-Grade-1 water
was used as a standard in
addition to the four aqueous
electrolyte solutions supplied in
sealed ampules as standards.
These solutions were 0.5 m KCl
(a W =0.984±0.003), 6.0 m
NaCl (a W = 0.760±0.003),
8.57 m LiCl (a W =0.500±
0.003) and 13.3 m LiCl (a W
=0.250±0.003). In the second
step, 19 aqueous solutions of
AR grade urea (1 x 10 -4 to 13 m
approx.) were made and their
water activities were
determined experimentally.
Experimentally determined
water activity values for ureawater
system were compared
with two sets of literature data
and an excellent agreement
was observed. 14 solutions of
uranyl nitrate were made
(~5x10 -4 to 5 m). The water
activity values for the uranyl
nitrate solutions were
determined and plotted in Fig.1
along with the values reported
in the literature
The osmotic coefficient was
derived from water-activity
values and based on that
activity coefficient of uranyl
nitrate in aqueous solution was
estimated. From water activity
values, vapour pressure of
aqueous solutions of uranyl
nitrate was also estimated and
is shown in Fig.2 along with the
literature data. Both match
well. Based on similar
methodology, activity
coefficients of various other key
and non-key solutes of interest
to reprocessing are being
evaluated. Incorporation of
these activity coefficients in the
mathematical models for
nuclear solvent extractions
would reduce the margin of
error in the predictions from the
computer simulations.
Fig.2 Variation of vapour pressure of
aqueous solution of uranyl nitrate
hexahydrate with concentration at
298.15 K and 0.l MPa. The present
experimental and calculated
data are compared with those
reported in the literature.
IV.B.3 Study of TBP-Nitric Acid Runaway Reaction
and Synthesis of Red-Oil
TBP nitric acid runaway
reaction was studied in a high
temperature-high pressure
autoclave (shown in Fig.1) and
red-oil was synthesized. It was
established that presence of
metallic nitrates was not
essential for red-oil formation
as thought earlier. Various
single-phase as well as twophase
experiments have been
completed.
From Fig.2 it is observed that
temperature profile had a
threshold of about 403K. This
Autoclave
Fig.1 A view of the experimental
setup for study of runaway chemical
reactions of interest to reprocessing
threshold temperature is
initiation temperature. From
Fig.3, it can be seen that the
amount of pressure generated
per mL of TBP exceeds even
500 psi /mL of TBP. It
underlines the absolute
necessity of removal of
entrained as well as dissolved
organics from the aqueous salt
solutions before they are
concentrated by means of
FUEL CYCLE 99