| AVS 63rd International Symposium & Exhibition | |
| Applied Surface Science | Thursday Sessions |
| Session AS-ThA |
| Session: | Advances for Complicated Sample Preparation Strategies and Complex Systems |
| Presenter: | David Willingham, Pacific Northwest National Laboratory |
| Authors: | D. Willingham, Pacific Northwest National Laboratory J. Tarolli, Pacific Northwest National Laboratory B. Naes, Pacific Northwest National Laboratory M. Rhodes, Pacific Northwest National Laboratory M. Dahl, Pacific Northwest National Laboratory A. Guzman, Pacific Northwest National Laboratory D. Burkes, Pacific Northwest National Laboratory |
| Correspondent: | Click to Email |
We aim to characterize the elemental and isotopic composition of uranium (U) metal and U metal alloys by electron microscopy (EM) and secondary ion mass spectrometry (SIMS). This type of characterization is important in understanding the behavior and performance of nuclear fuels and targets, and could potentially be utilized to interrogate processing history of the material. One example of such nuclear alloys is the uranium-molybdenum (U-Mo) system, development of which is being actively pursued throughout the world for use in research and test reactors (NA-23 Reactor Conversion Program), light water power reactors (DOE-NE Accident Tolerant Fuel), and pulse reactors (DoD – Army).
Previous EM characterization of approx. 19.75% enriched 235U-10wt% Mo fuel foils produced for the NA-23 Reactor Conversion Program revealed a complex grain structure of coarse, highly elongated regions interspersed with finer, more equiaxed grains. The distribution of grains was also organized within regions containing significant Mo variation produced during casting of this particular alloy. During post-irradiation examination, these regions and structures have been observed to behave differently depending upon the irradiation conditions that the fuel was subjected to. Elemental and isotopic heterogeneities in the fuel, particularly at boundaries between grains, have been hypothesized to lead to non-uniform swelling regions (i.e., volume growth) within the fuel. Understanding the elemental and isotopic distribution of alloying metals and other impurities is important to reasonably predict behavior of the fuel in a particular reactor system, ultimately enabling successful qualification for its use.
SIMS image analysis revealed several key characteristics of the U-Mo foil system. First, Mo rich grains could be observed by SIMS imaging. These grains are highly elongated along the length of the foil. Secondly, carbon inclusions, likely a result of U carbides, were found in the SIMS images. These inclusions can be seen to track with the previously observed Mo rich elongated grains. Finally, the U within the foil is much more homogenized than the Mo and appears to be much less mobile. The 235U/238U is consistent with the known value at approx. 20% enrichment of 235U and the U isotopic distribution is homogenous in all regions of the U-Mo foil. It is, therefore, likely that non-uniform swelling of these foils under irradiation is due primarily to U-Mo elemental heterogeneities rather than U isotopic variations.