TAF-ID Project

The Thermodynamics of Advanced Fuels - International Database (TAF-ID) Project aims to use the Calphad method to develop a thermodynamic database as a computational tool for understanding advanced fuel materials. This thermodynamic database allows predicting phase diagrams and thermodynamic properties of the phases.

The TAF-ID Project also provides a forum for information exchange on thermodynamic models, review of experimental data, software evaluation, thermodynamic assessments, etc.

Systems of interest: Fuel and related materials for Generation II, III, IV nuclear reactors

• Fuels: UO₂, (U,Pu,Am,Np)O₂, (U,Th)O₂, (U,Pu,Zr,Am,Np), UN, (U,Pu)C
• Fission products: Ba, Sr, Mo, Zr, Lanthanides (Ce, La, Nd, Gd), Metals (Pd, Ru, Rh, Te, Tc), volatile elements (Ag, Cs, I, Te)
• Structural and other materials: Fe-Cr-Ni, Zr alloys, Fe-Cr-Al-Y, Concrete (SiO₂-CaO-Fe_xO_y-Al₂O₃-MgO), SiC, B₄C

The TAF-ID database is suited to the following applications

• Fuel behaviour at high temperature under normal and off-normal conditions
• Influence of the Minor Actinides on the fuel thermodynamic properties
• Fission product « chemistry » and impact on irradiated fuels properties
• Solid/liquid phase transition
• Vaporisation behaviour
• Fuel/cladding chemical interaction at high temperature
• Fuel manufacturing

TAF-ID members' area (password protected | reminder)

TAF-ID database: working and public versions

Two versions of the TAF-ID database are being developed:

• A working version containing the description of all the systems to be investigated in the framework of the TAF-ID Project. This working version is accessible only to the signatories of the project. The version released in January 2023:
  • contains the following elements: Ag, Al, Am, Ar, B, Ba, C, Ca, Ce, Cr, Cs, Eu, Fe, Gd, H, He, I, La, Mg, Mo, N, Nb, Nd, Ni, Np, O, Pd, Pu, Re, Rh, Ru, Si, Sr, Ta, Tc, Te, Th, Ti, U, V, W, Y, Zr
  • is used to model specific binary and ternary systems and includes 237 binaries, 109 ternaries and 2 quaternaries.

TAF-ID working version (password protected | reminder)

• A public version containing a limited amount of data, e.g. only data that has already been published in open literature at the time of release. This version is be accessible to all NEA member countries upon request along with the signature of a non-disclosure agreement (NDA). The public version is available since December 2014 and was last updated in January 2018.

TAF-ID public version (password protected | reminder)

The TAF-ID database is developed in the Thermo-Calc format.

Goals of the TAF-ID project phases

Phase 1 (2013-2017)

During the first project phase, the project members created the TAF-ID database, starting from the FUELBASE database (CEA), with the addition of pre-existing systems from other project members (for oxide and metallic fuels). The project focused on the database development.

Phase 2 (2018-2022)

During the second project phase, the TAF-ID database development continued and the current version of the TAF-ID database (V15, January 2023) includes 43 elements, with 237 binaries included and 99 binaries assessed,109 ternaries assessed and 2 quaternaries assessed.

In addition, the project started validating the TAF-ID database with experimental work, including the funding of a post-doc to carry out this work and initiated benchmarking activities. A training course on TAF-ID was successfully organised in February 2021, gathering 70 participants online.

During this second project phase, TAF-ID members published 13 publications related to the TAF-ID project, including a review paper of the TAF-ID project and database.

Phase 3 (2023-2026)

For this third project phase, the programme of work includes:

• The TAF-ID database development/expansion with a focus on:
  
  • ATF Fuel systems (UO₂(Cr), UN, U₃Si₂, UC(O) fuels + Fission products) 
  • ATF Cladding systems (Cr-coated Zr, FeCrAl, SiC/SiC cladding (+H₂O))
  • Fuel-Coolant interactions (UO₂ with Na, Pb, or Pb-Bi coolant)
• The continuation of efforts to further validate the database: comparison between experimental data and calculated results for higher order systems including nitride fuels and experimental work funded by the TAF-ID Project
• Benchmark calculations to test software (Thermo-Calc, Open Calphad, FACTSAGE, Thermochimica) andversions of the TAF-ID
• The organisation of a training course
• The update of the TAF-ID public version
• The implementation of third party access to a protected version of the TAF-ID, including access to the documentation

Why is thermodynamic data for analyses involving nuclear fuel needed?

Detailed modelling of the fuel-cladding system is of major importance for several studies related to safety improvements, lifetime extension of Generation II and III reactors and the design of advanced Generation IV systems.

The use of thermodynamic data is needed for various analyses involving nuclear fuel: design of the fuel element; modelling of the fuel-cladding system under normal conditions in performance codes; analysis of fuel and cladding behaviour under severe accident conditions (pre-and post-fuel melting); the interaction of corium with the vessel; sacrificial materials (in-vessel); and concrete (ex-vessel).

These analyses may involve different types of fuel and cladding for Generation II, III and Generation IV systems:

• oxide, nitride, carbide, metal fuels, fuels with thorium, fuels with minor actinides, presence of fission products, etc.
• zircaloy, SiC, ODS steels, standard and advanced cladding materials, etc.
• structural materials: concrete, vessel, control rods, etc.

How is thermodynamic data calculated?

One of the ways to obtain thermodynamic data of the chemical properties of interest is by applying the CALPHAD method. This allows for the calculation of phase diagrams (composition and number of phases) over a large composition, temperature and pressure range as well as the thermodynamic properties of these phases (heat capacity, enthalpy, activity, partial pressure, etc.) which come from the mathematical function of the Gibbs energy of the phases that may form.

These functions are based on sub-lattice models derived from the crystalline structure of the different phases (a sub-lattice corresponding to a crystalline site). The free parameters in the model are optimised using a least-square minimisation method between experimental and calculated data. The experimental data consist of phase boundaries (liquidus, solidus, solubility limit, etc.) and/or thermodynamic data (heat capacity, mixing enthalpy, enthalpy of formation, activity, etc.). This approach requires a preliminary critical analysis of all experimental information available on the system before the modelling phase of the chemical species of interest.

External links

• Materials Modelling and Simulation for Nuclear Fuels (MMSNF) 2023 Workshop