PChem Seminar – Matthew P. Heaney

About the event

Speaker: Matthew P. Heaney

Group: Dr. Xiaofeng Guo

Title: Research Update: Thermal Expansion of Uranium Carbides

Abstract: Uranium carbides serve as a future fuel form for Generation IV reactors, in particular, reactors that will operate at higher temperatures than traditional water cooled reactors. Given the elevated temperatures, precise knowledge of the thermal expansion behavior of uranium carbides is critical for predicting dimensional stability and mechanical interaction in nuclear fuels at high temperatures. The particular uranium carbides of interest studied are uranium monocarbide (UC), uranium sesquicarbide (U2C3), and uranium dicarbide (UC2). All uranium carbides were studied using neutron diffraction, as this provides adequate sensitivity to the positions of carbon atoms that ordinary X-ray diffraction would not be sensitive to given that carbon is a low Z element. Such a method allows us to  more precisely explore the changes in C-C and U-C bond distances as a result of increasing temperatures. While all uranium carbides exhibited roughly monotonic lattice expansion, UC2, interestingly, exhibited a contraction in the C-C dimer bond distance, which might be indicative of a change in bonding/antibonding behavior within the unit cell.