Lance L. Snead
Fusion Materials Program
Oak Ridge National Laboratory
Post Office Box 2008
Oak Ridge, Tennessee 37831
865-574-9942
sneadll@ornl.gov

Dr. Snead's research is primarily on radiation damage to structural materials with emphasis on low activation materials. A brief outline of his research activities are as follows:
  • Silicon carbide and SiC composites have been discussed for fusion system application for more than twenty years with little progress towards their use. Over the past ten years substantial improvement have been made in both base properties and the radiation stability of these materials due in large part to a fundamental understanding of the mechanisms governing their behavior under irradiation. This work, which was primary conducted by Dr. Snead, and is close to demonstrating a true low activation material which would both reduce radioactive waste and enhance the safety of fusion systems. His current and planned research is to complete development of SiC composites by incorporating fibers with very low oxygen content and his newly developed SiC fiber/matrix interfacial structures. Preliminary studies show that these materials have higher strength and higher maximum operating temperatures than conventional materials, and will have superior radiation stability.
  • A second topic in the silicon carbide area to be explored by Dr. Snead deals with the radiation-induced amorphization of the crystalline SiC structure. Through a series of ion beam and neutron irradiations Dr. Snead has shown that a critical temperature exists, above which amorphization is impossible. A recent publication has also demonstrated that it is possible to amorphize SiC under neutron irradiation. A kinetic model has been developed to explain this behavior which postulates that amorphization is a function of not only temperature but also the irradiation dose rate. The amorphization of SiC is of critical importance because of the very large (>10% ) change in volume associated with amorphization of SiC, which would make the use of this material as a structural element in nuclear systems impossible. A secondary benefit to this research will be the description of the temperature dependent dose for amorphization of silicon, which would be of considerable interest to the electronics community which has been actively studying the kinetics of amorphization for ion implanted electronic devices.
  • In addition to structural ceramics such as SiC/SiC composites, ceramics are also being used for electrically insulating components. Dr. Snead and coworkers have recently completed a comprehensive test on the so-called radiation induced electrical degradation (RIED) phenomenon, which raised serious questions to the use of insulators such as alumina for fusion systems. The results of this series of experiments led to the assertion that RIED will not be an issue for fusion systems. A number of post-irradiation studies are in-progress to prove the non-existence of this phenomenon. Dr. Snead is currently increasing the effort into the thermal properties of insulating ceramics such as alumina, aluminum nitride as well as silicon carbide. In this work the large reduction in thermal conductivity caused by neutron irradiation of some ceramics will be measured and the results analyzed to provide a theoretical model of thermal conductivity as a function of radiation dose and temperature. The same approach will be used to in this work as was successfully used by Dr. Snead to develop a theoretically algorithm describing the degradation in thermal conductivity of carbon/carbon composites as a function of irradiation temperature and irradiation dose.
  • The final area which is considered a research milestone for Dr. Snead is the embrittlement of beryllium and vanadium materials. For the case of berylium, ITER relevant dose and temperature were explored to generate baseline data. For the case of vanadium, the focus of study has been to understand the low-dose, low-temperature embrittlement of the V-5Cr-5Ti alloy which has been most widely studied under the fusion program.
  • Book Chapter:

"Radiation Damage in Graphite," in Carbon Materials for Advanced Technologies, Elsevier Science ltd. (1997)

Selected Publications:

  1. L. L. Snead and J. C. Hay, "Neutron Amorphization of Silicon Carbide," accepted in Journal of J. Nucl. Materials (1998).
  2. L. L. Snead, S. J Zinkle, J. C. Hay and M. C. Osborne, "Amorphization of SiC Under Ion and Neutron Irradiation," Nuclear Instruments and Methods in Physics Research B 141 (1998) 123.
  3. L. L. Snead, M. C. Oborne, R. A Lowden, J. Strizak, R. J. Shinavski, K. L. More, W. S. Eatherly, J. Bailey, A. M. Williams, "Low Dose Irradiation Performance of SiC Interphase SiC/SiC Composites," J. Nucl. Mater. 253 (1998) 20.
  4. L. L. Snead and S. J. Zinkle, "Neutron Induced Thermal Resistance in Ceramics," submitted J. Applied Physics (1998).
  5. L. L. Snead and M. Osborne, "Radiation Damage in Advanced Silicon Carbide Composite Materials," accepted J. Nucl. Mater. (1997).
  6. L. L. Snead, R. H. Jones, A. Kohyama, P. Fenici, "Status of Ceramic Matrix Composites for Fusion Applications." J. Nucl. Mater. [233-237] (1996)
  7. L. L. Snead and S. J. Zinkle. "Amorphization and the Effect of Implanted Ions in SiC," MRS Symposium on Microstructure of Irradiated Materials. Ian Robertson, ed. (1996) 377-382.
  8. L. L. Snead and T. D. Burchell, "Thermal Conductivity Degradation and Annealing of Graphite at Low Temperature" J. Nucl. Mater. [234] (1995) 222-229.
  9. L. L. Snead, D. P. White and S. J. Zinkle. "Investigation of Radiation Induced Electrical Degradation in Alumina under ITER-Relevant Conditions,"J. Nucl. Mater. 226 (1995) 58-66.
  10. L. L. Snead and T. D. Burchell, "Reduction in Thermal Conductivity Due to Neutron Irradiation, 22nd Biennial Conference on Carbon. Extended Abstracts (1995) 774-775.
  11. L L Snead and O J Schwarz. "Advanced SiC Composites for Fusion Applications", J. Nucl. Mater. [219] (1995) 3-14.
  12. L. L. Snead, M. C. Osborne and K. L. More, "Effects of Radiation on SiC-based Fibers," J. Mater. Res. Vol. 10 [3] (1995) 736-747.
  13. L. L. Snead, " In-Core Measurement of DC Electrical Conductivity of Ceramics," J. Nucl. Mat. [212- 215] (1994) 1107-1112.
  14. L. L. Snead, "Development of Silicon Carbide Composites for Fusion," Fusion Technology, [24] 1.(1993) 65-82.
  15. L. L. Snead, R. A. Vesey. "A Moving Belt Divertor Concept". Fusion Technology, [24] 1. (1993) 83.
  16. L. L. Snead, S. J. Zinkle, D. Steiner. "Measurement of the Effect of Radiation Damage to Ceramic Composite Interfacial Strength," J. Nucl. Mater. [191-194] (1992) 566-570.
  17. L. L. Snead, S.J. Zinkle, D. Steiner. "Radiation Induced Microstructure and Mechanical Property Evolution of SiC/C/SiC Composite Materials,"J. Nucl. Mater. [191-194] (1992) 560-565.
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