RRFM 2009 Transactions - European Nuclear Society

CHARACTERIZATION OF THE MICROSTRUCTURE OF IRRADIATED
U-MO DISPERSION FUEL WITH A MATRIX THAT CONTAINS SI
D. D. KEISER, JR., A. B. ROBINSON, J. F. JUE, P. MEDVEDEV, AND M. R. FINLAY 1
Nuclear Fuels and Materials Division, Idaho National Laboratory
P. O. Box 1625, Idaho Falls, Idaho 83403 USA
1 Austalian Nuclear Science and Technology Organization
PMB 1, Menai, NSW, 2234,
Australia
ABSTRACT
RERTR U-Mo dispersion fuel plates are being developed for application in research reactors throughout
the world. Of particular interest is the irradiation performance of U-Mo dispersion fuels with Si added to
the Al matrix. Si is added to improve the performance of U-Mo dispersion fuels. Microstructural
examinations have been performed on fuel plates with Al-2Si matrix after irradiation to around 50% LEU
burnup. Si-rich layers were observed in many areas around the various U-7Mo fuel particles. In one local
area of one of the samples, where the Si-rich layer had developed into a layer devoid of Si, relatively
large fission gas bubbles were observed in the interaction phase. There may be a connection between
the growth of these bubbles and the amount of Si present in the interaction layer. Overall, it was found
that having Si-rich layers around the fuel particles after fuel plate fabrication positively impacted the
overall performance of the fuel plate.
1. Introduction
The United States Reduced Enrichment for Research and Test Reactors (RERTR) Fuel
development program is actively developing low enriched uranium (LEU) fuels for the world’s
research reactors that are currently fueled by uranium enriched to more than 20% 235 U [1].
To assess the performance of U-Mo dispersion fuels with Si-doped matrices, different reactor
experiments have been conducted using the Advanced Test Reactor (ATR). For the purpose of
conducting scanning electron microscopy examinations on irradiated samples, the RERTR-6
experiment has been of particular interest since the experiment was extracted from ATR over
three years ago, and as a result, small samples can be handled in the Electron Microscopy
Laboratory (EML). This paper will discuss results of recent microstructural characterization
using a scanning electron microscope (SEM) that was performed on a fuel plate with Al-2Si
matrix, irradiated as part of the RERTR-6 experiment. Optical metallography (OM) data will also
be included. Focus will be given to the partitioning behavior of Si amongst the microstructural
phases and how the presence of Si affects the development of interaction layers at the U-
7Mo/matrix interface. Comparisons are made to the other irradiation experiments that have
been reported for fuel plates with U-7Mo fuel dispersed in Al-2Si matrix.
2. Experimental
2.1 Irradiation Testing
The RERTR-6 experiment was the first experiment to test “second generation” U-Mo fuels
designed to overcome the fuel performance problems encountered in U-Mo/Al dispersions [2].
In this experiment, the fuel materials were tested to high burn-up under moderate flux and
moderate temperature conditions. The fuel plates were positioned edge-on to the core, and as a
result had a neutron flux across the widths of the fuel plates.
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