Cambridge 7th to 9th September
article posted 28 Apr 2015
Karishma Patel, PhD Earth Sciences, University of Cambridge
Karishma completed her undergraduate degree in Applied Science and Engineering at Queen's University
in her home country of Canada. Following her graduation she took a year off to investigate various
renewable energy applications in rural South America, before beginning an MPhil in Nuclear Energy
at the University of Cambridge. It was during this time that she identified the need for nuclear power
in addressing a growing global energy demand and a necessity for materials research on both ends of
the nuclear fuel life cycle.
Shortly after finishing her Masters she began a PhD with Ian Farnan delving into the wonderful world of
borosilicate glasses and their highly usable applications. She is currently in her third year of a doctoral
project focusing on radiation induced structural transformations, which has proved a tricky, but interesting foe.
Radiation effects on phase transformations in
borosilicate nuclear waste glasses
K. Patel*1, S. Peuget2, S. Schuller2,
I. Monnet3, C. Grygiel3, B. Boizot4 & I. Farnan1
Vitrification in a borosilicate glass is the technique currently employed for the immobilization of fission products and minor actinides arising from uranium dioxide nuclear fuel reprocessing. While extensive research exists on homogenous waste glasses, there is a lack of understanding when it comes to phase separated waste forms that results from high molybdenum content. Such high concentrations are expected in weapons grade waste or that arising from Generation IV reactors and may alter the chemical durability of the glass. This investigation seeks to address the mechanism behind structural evolutions induced by radiation in heterogeneous alkali and alkali earth borosilicate glasses as a means to assess the chemical stability of increased waste loading.
In order to develop accurate models of long-term internal radiative damage created by beta and alpha decay in nuclear waste forms, experiments were designed to disseminate the process into constituent parts that address both electronic and nuclear collisions. Irradiation studies were designed to test the hypotheses that radiation damage consistent with 1000 years of disposal would: (i) induce phase separation in homogeneous regions, (ii) proliferate the extent of phase separated regions or (iii) induce local melting along ion tracks and cause amorphisation of crystalline phases.
Swift heavy ion irradiations were conducted at GANIL using 95MeV Xe ions with fluencies of1.8x1014
This set of data gave insight into the high electronic stopping power region and the possible effects of ion tracks on phase separation phenomena. The kinetic data was also used to confirm whether structural transformations plateau in phase-separated samples as they do in complementary homogenous ones. Low electronic stopping was tested through 2.5MeV β-irradiation experiments conducted at LSI. Samples with absorbed doses of 0.77GGy and 1.34GGy exhibited formation of boron-oxygen hole centres and molecular oxygen, along with cationic clustering, in a manner proportional to dose. The last experiment conducted at CSNSM was designed to replicate ballistic events using 7MeV Au ions.
At a fluence of
, the structure was subjected to 1dpa, thereby testing the stability of water-durable crystalline phases within the glass, such as powellite.
Macro and microstructural evolutions were assessed using several techniques. Samples were analysed with a light microscope, SEM BS/EDS, Raman Spectroscopy, XRD and 11
B NMR in order to quantify the structural changes in amorphous and crystalline phases following irradiation. These changes have proved complex even in simplified systems, thus underlying the importance of mechanistic studies as opposed to bulk observations to model the complex behaviour of long-term internal radiation.
1 Department of Earth Science, University of Cambridge, Downing Street, Cambridge, CB23EQ, UK
2 CEA Marcoule, DEN/DTCD/SECM BP 17171 Bagnols sur Cèze Cedex, France
3 CIMAP, Bd Henry Becquerel BP 5133, 14070 Caen Cedex 5, France
4 Ecole Polytechnique, Laboratoire des Solides Irradiés (LSI) CEA/DSM/IRAMIS, CNRS 91128 Palaiseau Cedex, France