IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
Fig.2 Effect of matrix on the
signal intensity in the laser
desorption/ionization mass
spectrum of UO 2 (NO 3 ) 2 solution
most intense signal, followed by
UO 2+
and U + (Fig. 2b); with
+
PEO as the matrix, only UO 2
was observed (Fig. 2c); and
with TBP as the matrix UO + and
UO 2+
were the major species
with very small amount of U +
(Fig. 2d). The nicotinic acid
matrix seems to score over
others, since the total U gets
divided into all the three forms
(UO + , UO 2+
, U + ), and the
peaks are also sharper (better
mass resolution). Compared to
the no-matrix condition,
improvement in signal
intensities was observed most
with nicotinic acid as matrix (10
times), implying that use of this
matrix will involve considerable
reduction in the quantity of
sample required for the
analysis.
IV.A.4. Thermophysical Property Measurements on Urania-
Thoria and Urania-Gadolinia Solid
Solutions, and U-Zr Alloys
Uranium-thorium mixed
oxides are being considered as
the fuels for the thermal
reactors such as Advanced
Heavy Water Reactors and high
temperature gas cooled
reactors. Gadolinium is one of
the major fission products and
its oxide forms solid solutions
C P
(J/K/mol)
100
90
80
70
60
U 0.1 Th 0.9 O 2 Kopp's rule
U 0.5 Th 0.5 O 2 Kopp's rule
U 0.9 Th 0.1 O 2 Kopp's rule
U 0.1 Th 0.9 O 2 Drop
U 0.5 Th 0.5 O 2 Drop
U 0.9 Th 0.1 O 2 Drop
U 0.1 Th 0.9 O 2 DSC
U 0.5 Th 0.5 O 2 DSC
U 0.9 Th 0.1 O 2 DSC
400 800 1200 1600 2000
Temperature (K)
Fig.1 Heat capacity of (U,Th)O 2
Solid solutions
with uranium oxide in the oxide
fuel. Hence the thermophysical
properties of the solid solutions
of urania with thoria and
gadolonia are important. Heat
capacity data are available for
thoria rich (≤20 mol % urania)
mixed oxides only and that too
over a limited temperature
range. Enthalpy increments of
(U 0.1 Th 0.9 )O 2 , (U 0.5 Th 0.5 ) O2 and
(U 0.9 Th 0.1 )O 2 were measured
by inverse drop calorimetric
method using a high
temperature differential drop
calorimeter in the temperature
range 430-1805 K. Heat
capacity data were computed
from the measured enthalpy
increments.
Direct
measurements of the heat
capacity of these mixed oxides
were also carried out in the
temperature range 300-800 K
using a heat flux differential
scanning calorimeter. It can be
seen from Fig.1that the heat
capacity data of all the three
mixed oxides obtained by two
different calorimetric methods
are in very good agreement
with each other within 3% in
the overlapping regions and
that they are also in agreement
with the values computed using
Neumann-Kopp's rule.
There exists discrepancy in the
literature data for the heat
capacity and no data exist for
high temperature thermal
expansion of urania-gadolinia
solid solutions. Hence, heat
capacity measurements on
( U 0 . 9 G d 0 . 1 ) O 2 . 1 2 5 ,
(U 0.8 Gd 0.2 )O 2.187 and (U 0.5
Gd 0.5 )O 1.984 were carried out
using a heat flux differential
scanning calorimeter in the
temperature range 298-800 K
and the thermal expansion
measurements were performed
86 FUEL CYCLE