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Changes in Delta-Plutonium Due to Aging as Observed by Continuous in-situ X-Ray Scattering

  • Cheng K Saw (a1), Mark A. Wall (a2) and Brandon W. Chung (a3)


The aging in plutonium is predominantly caused by its internal self irradiation. The self-irradiation in Pu-239 is by the decay process of transmuting the Pu atom into uranium atom and emitting an α-particle. Most of the lattice damage comes from the uranium recoil resulting in Frenkel type defects consisting of vacancies and self-interstitial atoms, helium in growth and defect clusters and possibly even though it is not yet observed, the generation of voids. As part of the stockpile stewardship, it is important to understand the changes in the structure and microstructures and their correlations to the physical properties. Changes in the physical properties has direct relationship to the quality of the structure, in terms of formation of defects and defect clustering, accumulation of voids, grain boundaries, phase changes and etc. which can adversely affects the stability of the material. These changes are very difficult to monitor because of the high activity of the sample, high atomic number making x-ray and synchrotron probe into the bulk very difficult (neutron probe is not feasible) and the long life time which normally requires decades to measure. In this paper we describe the development of an in-situ in-house transmission x-ray diffraction (XRD) experimental technique used to monitor the structural changes in these materials. This technique calls for a very thin sample of less that 2 μm and to accelerate the aging process due to self-irradiation, spiked alloy of 7.5 weight percent of Pu-238 is used. This is equivalent to roughly 17 times the normal rate of aging. Current results suggest that over a period of 2.8 equivalent years, an increase of 0.5% in unit cell parameter is observed. The increase appears to be an abrupt jump at about 1.1 equivalent years, brought about by the collapsing of the atoms from the interstitials to the lattice sites. Further data analysis is on the way.



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Changes in Delta-Plutonium Due to Aging as Observed by Continuous in-situ X-Ray Scattering

  • Cheng K Saw (a1), Mark A. Wall (a2) and Brandon W. Chung (a3)


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