Research: Nuclear Materials, Minerals, Melts and Glasses

Triple containment rotor system developed to spin highly radioactive ceramics containing 10 wt% plutonium at ~200,000 rpm for high-resolution magnetic resonance analysis of next generation nuclear wasteforms.

Research is focussed on the question of material durability in nuclear waste disposal. The two major issues are internal attack of the material by radioactive decay and external attack by repository groundwater.
The scientific questions we ask are related to what happens to the structure of a crystalline ceramic or mineral when a highly energetic α–particle is emitted from a uranium or plutonium atom contained within it? How much of the structure is amorphised and what does the amorphised structure look like? How will this damage accumulate and affect the durability of the material in water? These are important questions if radionuclides are to be stored safely over long periods. We use a combination of techniques, but in the main nuclear magnetic resonance (NMR). These have allowed us to:

  • provide for the first time a measure of the number of atoms permanently displaced by a single α-decay event in zircon [1] using NMR ‘spin-counting’. This is five times greater than previously predicted [2]
  • obtain the first high-resolution NMR spectra of highly radioactive ceramics containing 239Pu and 238Pu at Pacific Northwest National Laboratory using a triply contained spinning system designed in Cambridge. This opens up the possibility of NMR spin-counting measurements on real nuclear wasteforms
  • show using ab initio calculations [3] that the ‘amorphous phase’ in 238U containing zircon is not constant in structure and that there is a change in density and an increasing amount of polymerisation as function of radiation dose. Also the nature of the defects accumulating in the crystalline phase changes with dose and can be identified [4]

Another important area of research is the nature of amorphous materials in general and in particular silicate melts and glasses. Here we ask how does the highly networked structure of the silicate liquid rearrange itself to allow flow? How does flow stop and how is the mechanism manifested in glass structure, in particular the homogeneity of the structure? For simple binary liquids we have shown that non-bridging oxygen redistribution halts at the glass transition [5]. We now ask how does the incorporation of different elements such as aluminium, titanium and boron affect the homogeneity of both the structure and the dynamics of the melts. To study this we have made a number of developments in high temperature NMR techniques and the theoretical understanding of the dynamic NMR spectra of nuclei such as 17O that have a quadrupole moment [6].

Teaching

Course A NST IA Materials and Mineral Sciences
Organisation of Atoms in Crystals
Course Coordinator NST IB Mineral Sciences

References

  1. Farnan, I. & Salje, E. K. H. The degree and nature of radiation damage in zircon observed by Si-29 nuclear magnetic resonance. Journal of Applied Physics 89, 2084-2090 (2001).
  2. Farnan, I., Cho, H. & Weber, W. J. Quantification of actinide α-radiation damage in minerals and ceramics. Nature 445, 190-193 (2007).
  3. Balan, E., Mauri, F., Pickard, C. J., Farnan, I. & Calas, G. The aperiodic states of zircon: an ab initio molecular dynamics study. American Mineralogist 88, 1769-1777 (2003).
  4. Farnan, I., Balan, E., Pickard, C. J. & Mauri, F. The Effect of Radiation Damage on Local Structure in the Crystalline fraction of ZrSiO4: Investigating the 29Si NMR Response to Pressure in Zircon and Reidite. American Mineralogist 88, 1663-1667 (2003).
  5. Farnan, I. Oxygen bridges in molten glass. Nature 390, 14-15 (1997).
  6. Kristensen, J. H. & Farnan, I. Measurement of molecular motion in solids by nuclear magnetic resonance spectroscopy of half-integer quadrupole nuclei. J. Chem. Phys. 114, 9608-9624 (2001).

Older Publications by Dr Ian Farnan


Publications: 2006-Present

Last updated on 19-Jul-11 14:04