Nuclear Fuel Cycle
Nuclear power plants all over the world, with the exception of
France, practice the "once-through" fuel cycle, wherein the used
fuel removed from the reactor is destined for ultimate disposal in
a repository. However, this results in less than optimal use of
resources, as the used fuel can be reprocessed to recover fissile
and fertile material for reuse. It is anticipated that nuclear
fuel cycle will transition through a limited recycle (reuse of
fissile material in existing reactors) to, ultimately, a "closed"
cycle that utilizes fast breeder and burner reactors to utilize
fully all the fissile and fertile resources. The fuel cycle
research includes investigations into issues related to efficiency
and enhancements in aqueous and electrochemical reprocessing as
well as treatment of waste streams such as off-gas emissions from
the reprocessing operations.
Reactors-Hybrid Energy Systems
The nuclear reactors of the future are expected to have
flexibility to provide, in addition to electricity, thermal energy
(heat) as an output for direct utilization in chemical processes.
Thus nuclear heat can be harnessed for the production of synthetic
transportation fuels, hydrogen, or any other application that
requires high temperatures. These so-called Gen IV reactors will
operate at higher temperatures than the current generation of
light water reactors, and utilize heat transfer media such as
helium, liquid sodium, molten salts, etc. The research conducted
in this field includes modeling and simulation of the behavior of
the advanced reactor-heat transfer system including the
development of control strategy, and development of hybrid systems
for production of synthetic transportation fuels.
Teaching and Pedagogy
The effectiveness of teaching as measured by the level of student comprehension can be greatly enhanced by turning the students into active participants in the learning process. This is particularly important for chemical engineering courses that require application of advanced mathematical concepts to complex topics. Effective teaching techniques were implemented in the Transport Phenomena courses by incorporating experiments focused on mass transfer concepts. The hands-on activity in the laboratory and the data collection-analysis-inference exercise helped the students link the theoretical concepts to practical manifestations, turning them into active learners.
Hydrogen is presumably the transportation of the future, and the
U.S. Department of Energy has developed a Hydrogen Posture Plan
and National Roadmap for transitioning to a hydrogen economy. The
hydrogen and energy related research includes production via
nuclear energy-driven thermochemical cycles, utilization, life
cycle assessment to ascertain the environmental impacts, and
evaluation of primary energy sources for future.
Acid Mine Drainage Remediation
Acid mine drainages (AMDs) are contaminated acidic bodies of water that are formed, primarily due to microbial oxidation of sulfidic ores. AMDs containing high concentrations of sulfate and metal ions can be remediated by metal hydroxide precipitation using lime. However, it requires expensive reagents and results in generation of large quantities of mixed metal hydroxide sludge that has to be treated as hazardous waste. An attractive alternative treatment utilizes sulfate reducing bacteria (SRB) to convert sulfate ion to sulfide, that can then react with metal ions and precipitate metal sulfides that have even lower solubility than hydroxides. The AMD drainage research focusses upon:
1. Determination of biokinetics of sulfate
reduction using mixed cultures of SRB
2. Determination of toxic/inhibitory impact of metal ions on SRB activity
3. Quantification of inhibitory effect of sulfide, and
4. Development of processes for metal separation/recovery
Biosorption and Biofiltration
Metal ions can be recovered from aqueous waste streams by sorbing them on a biosorbent, such as, activated sludge. Equilibria and kinetics of sorption of copper and zinc on non-viable activated sludge were determined using a packed column. Biosorption study using continuous column configuration represents a significant departure from the suspended, well mixed batch systems used in most biosorption studies.
Technological feasibility of microbial degradation of volatile
organic chemicals (VOCs) was demonstrated using air biofiltration.
A comprehensive mathematical model was developed for the
biofilters. The salient features of the model included: (1). the
use of monod kinetics to describe intrinsic biodegradation
kinetics, (2) Incorporation of external mass transfer
(gas-liquid) and (liquid-solid) resistances, and (3) consideration
of diffusive resistances within the biofilm. Intrinsic
biodegradation constants for the target substrates were determined
in a microbiofilter. The biokinetic constants were used in
numerical simulations of the model and the theoretical predictions
correlated well with the experimental observations, indicating the
validity of the model.
Multiphase Reactor Design
A number of industrial processes (hydrometallurgical operation,
coal desulfurization) utilize three phase (gas, liquid and
catalytic/non-catalytic solid) sparged reactors. The reactions of
individual solid particles were modeled using shrinking core and
simultaneous diffusion with reaction models. These models combined
with the flow models for the reactors led to overall models for
fluidized bed and bubble column slurry reactors. Simulations of
overall process models yielded performance charts that relate the
conversion of the solid phase with respect to the residence time
in the reactor. The conversion, or extent of reaction is a
function of the operating conditions and properties of the
reactants. The validity of the models was tested by comparison of
the predicted conversions with the observed experimental data.