Phase relations in the quaternary Fe–Pu–U–Zr system

The phase diagram in the quaternary Fe–Pu–U–Zr system was established at 923 K in the uranium-rich region to understand better the compatibility between the metal fuel and stainless steel cladding in a fast reactor. The experimental phase relation data obtained in this study was applied to the thermodynamic methodology for construction of the phase diagram. The calculated phase diagram was consistent and well within the experimental data. The applicability of the thermodynamic model to other temperatures was confirmed by comparing the present results of differential thermal analysis with the calculated phase diagrams. These consistencies mean that both the thermodynamic model and the assessed parameters in the binary and ternary subsystems developed so far are reasonable. The calculated phase diagram established in this study was also in good agreement with the analysis of the diffusion zone in tests on Pu–U–Zr/Fe couples. This suggests that the diffusion zone formed at the fuel–cladding interface in the reactor system can be assessed using the phase diagram in the quaternary Fe–Pu–U–Zr system.