Interdiffusion and reactions between U–Mo and Zr at 650 °C as a function of time

Abstract

Development of monolithic U-Mo alloy fuel (typically U-10wt.%Mo) for the Reduced Enrichment for Research and Test Reactors (RERTR) program entails a use of Zr diffusion barrier to eliminate the interdiffusion-reactions between the fuel alloy and Al-alloy cladding. The application of Zr barrier to the U-Mo fuel system requires a co-rolling process that utilizes a soaking temperature of 650°C, which represents the highest temperature the fuel system is exposed to during both fuel manufacturing and reactor application. Therefore, in this study, development of phase constituents, microstructure and diffusion kinetics of U-10wt.%Mo and Zr was examined using solid-to-solid diffusion couples annealed at 650°C for 240, 480 and 720 hours. Phase constituents and microstructural development were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Concentration profiles were mapped as diffusion paths on the isothermal ternary phase diagram. Within the diffusion zone, single-phase layers of -Zr and -U were observed along with a discontinuous layer of Mo 2 Zr between the -Zr and -U layers. In the vicinity of Mo 2 Zr phase, islands of -Zr phases were also found. In addition, acicular -Zr and U 6 Zr 3 Mo phases were observed within the -U(Mo) terminal alloy. Growth rate of the interdiffusion-reaction zone was determined to be 1.81 x 10 -15 m 2 /sec at 650°C, however with an assumption of a certain incubation period.

Effects of heat treatment on U–Mo fuel foils with a zirconium diffusion barrier

“…75 × 10 -16 m 2 /sec), and an activation energy of 219.4KJ/mol (with an assumption of an incubation time of 159 hours at 650°C). 21 Again, the UZr 2 phase was not observed in that study. The reason for the difference is not clear; impurities, such as oxygen and iron on the Zr/U-Mo interface, and the cooling rate after annealing could affect the formation of phases at the interface.…”

Intermetallic formation and interdiffusion in diffusion couples made of uranium and single crystal iron

“…The formation of UO 2 is unlikely to be avoided. Previous studies have noticed the existence of such incubation periods at low temperatures due to existence of diffusion barrier [16]. At a time shorter than this incubation period, diffusion is very limited and interfacial compound formation is not initialized.…”

“…The integrated interdiffusion diffusion coefficient of phase v could then be calculated by integrating the flux over intermetallic phase of v [16]. The intermetallic phases in the U-Fe systems, shown in Fig.…”

“…The approach used by Huang, et al [6,[13][14][15][16] can be used to calculate integrated intrinsic diffusion coefficients in a binary system like U-Fe without significant changes. The intrinsic fluxes can be obtained by using:…”

Atomistic simulations of the small xenon bubble behavior in U–Mo alloy

“…The presence of Xe bubbles in U-Mo alloy fuel can drastically change its mechanical properties and thermophysical properties, especially lead to an important swelling, which can have dramatic consequences for the safety of nuclear devices. This is the reason why lots of theoretical and experimental studies [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] have been undertaken to understand the behavior of this U-Mo alloy fuel under irradiation, especially the effect of fission gas bubbles on the fuel properties. However, the behavior of small Xe bubbles, especially the basic processes governing its migration, coalescence and the release of Xe atoms from the U-Mo alloy fuel, has not been understood clearly.…”