| Abstract Scope |
The CALPHAD (CALculation of PHAse Diagrams) method couples phase diagrams and thermochemistry to predict phase equilibria, thermophysical properties and diffusion/precipitation kinetics. This talk will highlight recent studies from the literature to illustrate the versatility of CALPHAD based tools across multiple nuclear applications.
In weld overlay cladding (e.g. for safe ends), CALPHAD has helped guide filler metal selection and even development of new materials to resist various forms of weld cracking. For dry storage and disposal, kinetic models using CALPHAD have been applied to NiCrMo alloys selected for waste disposal canisters. The models analyzed diffusion controlled transformations and precipitation of ordered Ni₂Cr and δ phase in Alloy 22 surrogates, providing insight to mitigate long-term degradation in spent fuel casks.
For fusion applications, joining tungsten to steel is difficult because of melting point disparities and brittle intermetallics. One study examined diffusion bonded tungsten–steel interfaces and employed CALPHAD to explore joining parameters, thermal stability and diffusion kinetics, offering guidance for designing interlayers for plasma facing components.
Beyond structural materials, CALPHAD is also useful for advanced fuel and fuel cladding design, as well as understanding behavior and life of existing rods. For example, assessments of the zirconium–oxygen–hydrogen system shows that dissolved hydrogen increases the oxygen content of the prior β phase and reduces ductility in zirconium based fuel cladding. Together, these case studies demonstrate how CALPHAD based tools accelerate the design of alloys, cladding, joints and fuels that withstand the harsh environments of nuclear fission, fusion and advanced microreactor systems. |