b'Modeling InternalInternal melting and solidification are modeled in state-of-Material Melting the-art nuclear fuel performance simulation code.T o model internal material melting or solidifying, the enthalpy form of the heat conduction governing equation was implemented into BISON and MOOSE conduction module. During a phase change produced from internal nuclear heating or after as the fuel cools, the energy change is not entirely reflected by the change in temperature due to the required heat of fusion energy PROJECT NUMBER:of the phase change. For heat conduction governing equation models that solve 21A1055-020 for the temperature field solution, treatment of this behavior can be complicated. The enthalpy form of the heat conduction equation solves for the enthalpy field TOTAL APPROVED AMOUNT:solution, which continuously changes even during phase change as energy is $125,000 over 1 year changed. MOOSE kernels for each term in the governing equation were created. A PRINCIPAL INVESTIGATOR:MOOSE fixed temperature Dirichlet boundary for the enthalpy form was created. Adam Zabriskie Temperature-dependent solidus and liquidus temperature material models for uranium-plutonium-zirconium were added to BISON. All code additions include CO-INVESTIGATOR: documentation of the theory and user manual and regression tests for software Stephen Novascone, INL quality assurance requirements of both MOOSE and BISON. Both standard and automatic differentiation forms were provided for the new code. Unfortunately, an enthalpy form material model converter was not completed, preventing the use of the created code on a BISON assessment.The enthalpy form of the heat conduction equation whereis density, E is a change in enthalpy from a reference state enthalpy,and S are derived material properties from specific heat, thermal conductivity, and heat of fusion, and q is a volumetric heat source.36'