Emily Siska

Emily Siska

Emily Siska preparing a resistive heated DAC

Status: Ph. D. Chemistry, 3rd year

Project: Development of Novel Wasteforms for the Long Term Storage of Nuclear Waste

Advisor: Barbara Lavina and Paul Forster

Email: siskae@unlv.nevada.edu

 

Education:

B.S., Chemistry, University of Nevada Las Vegas, Las Vegas, NV 2012

 

Research:

Nuclear power makes up 5.7% of the world’s energy consumption and is expected to grow every year. Currently, the most widely used waste form is borosilicate glass. Although glass and ceramic waste forms have proven to be durable and sufficient at immobilizing many radionuclides; there are some radionuclides that cannot be sufficiently captured and contained by glasses or ceramics. There is a need to design new waste forms that have low dissolution and leaching rates and high durability. Radioisotopes including 129I, 85Kr, 135Xe, and 99Tc with long half-lives need to be isolated from human and environmental exposure for thousands – and in some cases millions of years. This research project aims to explore novel waste forms to immobilize these problematic radionuclides.

My research focuses on two different types of waste forms. The first is the immobilization of radionuclides by encapsulation into zeolites. Zeolites are a class of mineral with a crystalline structure that is made up of a rigid silicate framework that form pores and channels. They are composed of naturally abundant compounds and can be synthesized with inexpensive, non-toxic materials. Typically, the pore and channel system of zeolites lends itself to industrial applications such molecular sieving. However, sodalite, has a unique structure that is made of face sharing cages and is devoid of channels. Once a guest atom/molecule has been incorporated or inserted into a cage, it would be difficult for it to diffuse out provided the windows size is small enough. With moderate pressure and temperature the normally rigid framework can become flexible and its windows can accommodate diffusion of large guest atoms/molecules. Using a diamond anvil cell equipped with internal and external resistive heaters we are investigating the insertion of different guest molecules into the host sodalite. Insertion is determined by monitoring changes in unit cell volumes by means of synchrotron x-ray diffraction. The second type of waste form being explored is the formation of stable compounds of radionuclides. Technetium is not abundant naturally and is primarily found as a fission by-product in the uranium fuel cycle. Experimental work with analogs of Tc and computational studies suggest the existence of stable technetium nitride compounds. However, researchers have presently been unable to synthesize them at ambient conditions. High pressure and temperature have been previously exploited to explore novel chemistries for many elements, and may be the key to creating stable technetium nitride compounds. Synthesis of technetium nitride compounds is being investigated across a wide range of temperatures and pressures using double-sided laser heated diamond anvil cell. We will use in situ x-ray diffraction to monitor the synthesis and determine the crystal structure.

 

National Laboratories:

  • Argonne National Laboratory, Advanced Photon Source, Sector 16 – IDB. Powder and Single Crystal X-ray Diffraction.
  • Lawrence Berkley Laboratory, Advanced Light Source 12.2.2. Powder X-ray Diffraction.

 

Professional schools & workshops:

  • 17th National School on Neutron and X-ray Scattering School: learned how to utilization neutron and x-ray facilities. Lectures on the principles of scattering theory and application of scattering methods to a variety of scientific subjects. Also conducted short experiments at Argonne’s Advanced Photon Source and Oak Ridge’s Spallation Neutron Source and High Flux Isotope Reactor facilities.
  • HPCAT workshop on high-pressure time-resolved synchrotron techniques: lectures on the advances in synchrotron sources, x-ray optics, fast area detectors, IR lasers and adaptable remote pressure controls in relation to time-resolved experimental techniques for studying materials at extreme pressure and temperature conditions.
  • 2015 IUCr High-Pressure Workshop, Brazilian Synchrotron Light Laboratory: Presentations on high-pressure crystallography, crystal structure determination, phase transitions and their kinetics, new materials synthesis,

 

Awards:

  • Malcolm F. Nical Graduate Scholar, 2014-2015
  • Graduate and Professional Student Association Research Sponsorship Funding, Spring 2015, Fall 2015, Summer 2016
  • 2nd Place for Outstanding Presentation, Graduate College & Graduate and Professional Student Association Annual Research Forum, University of Nevada Las Vegas, 2015

 

Publications:

  • Mwilu, S. K., Siska, E., Baig, R. N., Varma, R. S., Heithmar, E., & Rogers, K. R. (2014). Separation and measurement of silver nanoparticles and silver ions using magnetic particles.Science of the Total Environment472, 316-323.
  • Mast, D. S., Kim, E., Siska, E. M., Poineau, F., Czerwinski, K. R., Lavina, B., & Forster, P. M. (2016). Equation of state for technetium from X‐ray diffraction and first-principle calculations.Journal of Physics and Chemistry of Solids95, 6-11.
  • Huynh, K. A., Siska, E., Heithmar, E., Tadjiki, S., & Pergantis, S. A. (2016). Detection and Quantification of Silver Nanoparticles at Environmentally Relevant Concentrations Using Asymmetric Flow Field–Flow Fractionation Online with Single Particle Inductively Coupled Plasma Mass Spectrometry.Analytical chemistry,88(9), 4909-4916.

 

Presentations:

  • Novel Radionuclide Wasteforms Prepared Under Pressure. Poster session at HPCAT workshop on high-pressure time-resolved synchrotron techniques, Argonne National Laboratory, 2014

 

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