| AVS 61st International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Monday Sessions |
| Session AC+AS+MI+SA+SS-MoM |
| Session: | Spectroscopy, Microscopy and Dichroism of Actinides and Rare Earths |
| Presenter: | Martin Brierley, AWE, UK |
| Authors: | M. Brierley, AWE, UK J.P. Knowles, AWE, UK M. Preuss, University of Manchester, UK A.H. Sherry, University of Manchester, UK |
| Correspondent: | Click to Email |
Under certain conditions plutonium is able to form plutonium hydride during long term storage [1]. Plutonium is radioactive, decaying via release of an alpha particle. Alpha particles are particularly damaging within the body and every attempt should be made to limit the distribution of loose material. Plutonium hydrides have been shown to be pyrophoric when exposed to oxygen; a reaction that could potentially liberate loose particulate outside of suitable containment.
Previous work into the hydriding rate of plutonium has investigated the reaction rate of various hydrides on the surface of these materials; specifically the nucleation rate, the lateral growth rate and the specific hydriding rate [2, 3]. Plutonium is a reactive metal and quickly forms a semi-protective oxide layer in air. Upon exposure of an oxide-covered sample to hydrogen, hydride is formed at discrete sites on the surface, which then grow radially across the surface [1]. Recent work has suggested a grain boundary enhanced growth rate [4].
In the present study, the microstructure associated with selected plutonium hydride growth sites was studied to provide information regarding the nucleation and growth mechanisms that govern the formation of plutonium-hydride. The samples were ground to 600 grit and evacuated before being exposed to ultra-pure hydrogen at pressures between 10 mbar and 1000 mbar for sufficient time to have nucleated a number of hydride sites.
Post-test analysis was performed using Scanning Electron Microscopy (SEM) and Optical Microscopy (OM) to determine the microstructure of the hydride growth sites. The morphology of individual hydride growth sites indicates that the hydride-metal interface has a highly discontinuous boundary, resulting from enhanced grain boundary diffusion and spears of transformed material; the microstructure within the plutonium hydride growth sites indicates that a preferred growth habit was adopted by the hydride product.
References
[1]J.M. Haschke and J.C. Martz, Los Alamos Science, 26 (2000) 266-267
[2] G. W. McGillivray, J. P. Knowles, I. M. Findlay, M. J. Dawes, J. Nucl. Mater. 385 (2009) 212-215.
[3] C. Kenney, R. Harker “Specific Hydriding Rates of δ -Plutonium”, Presentation at Pu Futures, Keystone Colorado (2010)
[4] C.K. Saw, J.M. Haschke, P.G. Allen, W. Mclean II, L.N. Dinh, J. Nucl. Mater. 429 (2012) 128–135