Publications and Presentations

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.

Advanced 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

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.