| AVS 63rd International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Thursday Sessions |
| Session AC+AS+SA-ThM |
| Session: | Chemistry and Physics of the Actinides and Rare Earths |
| Presenter: | Martin Brierley, AWE |
| Authors: | M. Brierley, AWE J.P. Knowles, AWE |
| Correspondent: | Click to Email |
The reaction of plutonium with hydrogen creates plutonium hydride in an energetic process which often liberates the reaction product as a powder. Plutonium hydride is pyrophoric; therefore study of the reaction product usually requires that it is passivated by careful exposure to oxygen prior to removal from the reaction chamber. The passivation process is highly energetic with the potential to significantly affect the microstructure of the reaction product and surrounding metal. In this study we used a scanning electron microscope with an adjoining reaction chamber to maintain vacuum between reaction and analysis to grow plutonium hydride and subsequently analyse the reaction products as formed.
Initial work on electro refined Pu gave a slow reaction to hydrogen, requiring an in situ heat treatment to form hydride. Analysis of the reaction product was made in vacuo following reaction, preventing oxygen from accessing the sample. Subsequent cross sectional analysis of the reaction product morphology was performed, showing a coating of a hydride product layer with an open structure under the original surface oxide [1].
A sample of mixed α/δ phases was successively exposed to hydrogen for increasing durations of 60, 7200 and 70320 s. No evidence of reaction was evident following the 60 s and 7200 s exposures, unlike that observed in experiments on gadolinium [2] and uranium [3]. Following the 70320 s exposure, 96 % of the available hydrogen was consumed and several large anisotropic reaction sites had formed. The hydride sites on this mixed phase sample exhibited anisotropic growth similar to δ-stabilised plutonium samples investigated previously [ 4 ]. Deformation of the δ-phases surrounding hydride sites occurred via slip processes. Cracks formed in the overlying oxide layer above the deformed material allowing facile access for hydrogen to reach fresh Pu at the metal/oxide interface. Subsequent cross sectional analysis revealed anisotropic growth of hydride reaction sites, strongly supporting our previously proposed mechanism for anisotropic growth [4]. The α-phase domains resisted deformation and instead transferred the stresses from the hydride reaction front further into the surrounding metal. Post experimental cross sections through reaction sites suggest that hydride regions associated with α-domains had not undergone complete reaction.
References
1. M. Brierley et al., Journal of Nuclear Materials 469 (2016) 39-42
2. G.M. Benamar, et al., Journal of Alloys and Compounds 520 (2012) 98– 104.
3. R.M. Harker, A.H. Chohollo, MRS Online Proceedings Library Archive, 1444 (2012) 189
4. M. Brierley, et al., Journal of Nuclear Materials 469 (2016) 145-152