| Čoahkkáigeassu: | Zirconium is non-corrosive material and has high melting point. Due to its
low neutron capture cross section, zirconium can be used as cladding material
replacing silicon carbide (SiC) in nuclear fuel kernel. As cladding material,
hafnium content in zirconium must be below 0.01% or 100 ppm. This because
hafnium has neutron capture cross section 470 higher than zirconium. This
property of hafnium will disturb the fission nuclear reaction. Beside that hafnium
can be used as controlling rod materials so the separation of these two materials
is very important.
However, zirconium and hafnium are very difficult to separate due to
similarity in their chemical properties and ionic radii. Separation method based
on differences in adsorption properties has been applied such as continuous
annular chromatography (CAC) using cation resin. The separation effectiveness
strongly depends on diffusivity and adsorption affinity of components in the bed of
resin. In this work, adsorption constant of components in Dowex 1 X8 anion resin
were determined by using batch experiment. Beside that the diffusivities of each
component through the resin bed also determined in this work. The separation of
zirconium and hafnium using annular chromatography was simulated. The effect
of feed and eluent flowrate, rotation speed and height of resin on CAC resolution
was studied in order to suggest the optimum condition for separation process.
Three different isotherm equilibrium models were proposed in order to fit
the equilibrium experimental data. Simulation showed that distribution
equilibrium model could fit the experimental data very well. The distribution
coefficient for zirconium and hafnium were 6.16x10-3dm3/g resin and 4.72x10-3dm3
/g resin respectively. A column glass resin was used to determine the
diffusivities of zirconium and hafnium. Two mathematical models were proposed
such as rate-based model (RBM) and equilibrium-based model (EBM) to fit the
experimental data. Simulation result showed that the RBM could fit the
experimental data better than EBM. The diffusivities of zirconium and hafnium
were 8.78x10-5cm2/s and 7.32x10-5cm2/s respectively. Meanwhile the overall
mass transfer coefficient of zirconium and hafnium were 2.35x10-21/s and1.11x10-21/s respectively. The simulation result of separation zirconium and
hafnium using CAC based on equilibrium model showed that zirconium and
hafnium could be separated using CAC with diameter 20 cm and 20 cm of resin
height. The feed and eluent flowrate was 0.03 cm/s and the rotation speed was
0.209 rpm.
|
|---|