Investigation of the solid/liquid phase transitions in the U–Pu–O system

• DOI: 10.1016/j.calphad.2022.102523
• Publication Date: 2023-01-18T19:12:20Z
• Authors: P. Fouquet-Métivier; P.M. Martin; D. Manara; K. Dardenne; J. Rothe; P.C.M. Fossati; C. Guéneau
• Keywords: Liquidus; Solidus; Stoichiometry; Phase boundary; Ternary numeral system

Mixed oxides of uranium and plutonium U1-yPuyO2-x are currently studied as reference fuel for Sodium-cooled Fast Reactors (SFRs). To predict the margin to melting, an accurate description both solidus liquidus temperatures these materials is crucial. In this work, after a critical review literature data, parameters liquid phase CALPHAD models Pu–O U–Pu–O systems reassessed based on model Guéneau et al.. A good agreement between calculated selected experimental data obtained. Using model, melting behaviour U1-yPuyO2±x then function content oxygen stoichiometry. The congruent mixed found be shifted towards low O/M ratios compared end-members (UO1.97 PuO1.95). temperature nearly constant (3130–3140 K) along ternary boundary from UO1.98 U0.55Pu0.45O1.82 decreases with Pu maximum approximately 3040 K PuO1.95. This observation explained by stabilisation hypo-stoichiometric due increase configurational entropy at high formation vacancies related cation mixing. influence atmosphere used in laser heating experiments stoichiometry sample its investigated. determination ratio tests using XANES also reported. simultaneous presence U6+, U5+, U4+, Pu3+ Pu4+ observed, highlighting occurrence charge compensation mechanisms. samples highly oxidised air whereas close (O/M = 2.00) argon. These results computed solidification paths. work illustrates complex fuels highlights need method accurately describe high-temperature transitions system.