RRFM 2009 Transactions - European Nuclear Society

660 °C, but since in the former meat section only U 0.9 Al 4 particles are measured, we should
conclude, based on the binary diagram, that the temperature in this zone stayed below
731 °C.
The fuel plate in this zone is thus reduced to a melt which is still covered by a small oxide
layer on the outer surface. Zone D therefore corresponds to the start of Area 3 in figure 2.
The microstructure of sample S2 seems at first very similar to the structure observed in Zone
D of sample S1. However, local quantitative analysis (and by reference to literature [9])
shows that in the area of S2 following zone D of S1, the U 0.9 Al 4 particles are still found in
addition to large angular UAl 3 particles. More towards the center of the fuel plate, UAl 3
dendrites are seen. At the extremities of these dendrites, eutectic droplets are observed
(gray particles in fig. 8e). With these observations and the assumption that the average
composition of the melt is around 72-75 wt% Al (supported by EDX and image analysis), one
can see from the binary diagram (Fig. 9) that the temperature in this location has reached
900 -950 °C.
4 Conclusion
A local coolant flow blockage caused the partial melting of two fuel plates. Detailed analysis
shows that the microstructure of the melted plate is defined by full fission gas release, the
complete reaction between UAl x fuel and the Al matrix and weakening of the cladding. All
phenomena were triggered by the increasing temperature, which has probably reached in the
center of the fuel plate, locally about 1000 °C before the reactor scrammed.
The different stages of fission gas release and the thermodynamic evolution of the phases
could be clearly identified.
References
[1] F. Joppen in: The proceedings of the 9th International Topical Meeting on Research
Reactor Fuel Management (RRFM), Budapest, Hungary (2005).
[2] M. Adorni, A. Bousbia-Salah, T. Hamidouche, B. Di Maro, F. Pierro and F. D'Auria, Annals
of Nuclear Energy 32 (2005) 1679-1692.
[3] Q. Lu, S. Qiu and G. H. Su, Nuclear Engineering and Design
doi:10.1016/j.nucengdes.2008.06.016 (2008).
[4] D. Stahl, Fuels for research and test reactors, status review, ANL-83-5 (1982).
[5] A. Leenaers, E. Koonen, Y. Parthoens, P. Lemoine and S. Van den Berghe, J. Nucl.
Mater. 375 (2008) 243–251.
[6] S. Van den Berghe, W. Van Renterghem and A. Leenaers, J. Nucl. Mater. 375 (2008)
340-346.
[7] T. Shibata, K. Kanda, K. Mishima, T. Tamai, M. Hayashi, J. L. Snelgrove, D. Stahl, J. E.
Matos, F. N. Case and J. C. Posey in: The proceedings of the International meeting on
Research and Test Reactor Core Conversions from HEU to LEU fuels, ANL (1982).
[8] M. E. Kassner, P. H. Adler, M. G. Adamson and D. E. Peterson, Journal Of Nuclear
Materials 167 (1989) 160-168.
[9] V. Y. Zenou, G. Kimmel, C. Cotler and M. Aizenshtein, Journal of Alloys and Compounds,
329 (2001).
[10] O. Tougait and H. Noel, Intermetallics 12 (2004) 219-223.
340 of 455