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.

Available tools for thermodynamic calculations

Currently, several tools are used in various laboratories and organisations which are part of the NEA:

Canada: database on uranium oxide developed at RMCC
France: FUELBASE developed at CEA
Japan: a database on metallic fuels developed at CRIEPI and one on corium for BWR developed at JAEA
The Netherlands: TBASE developed at NRG
United States: several databases developed at ORNL, INL and LLNL

Each of these databases allows the performance of studies on only a few of the chemical properties described above. The unification of these separate databases will greatly benefit all the organisations, each of which relies nowadays solely on its own experience, data, know-how and resources for the use, maintenance, development and the validation of its database.

Project organisation

The Thermodynamics of Advanced Fuels - International Database (TAF-ID) Project was established in 2013 to provide a comprehensive, internationally recognised and quality-assured database of phase diagrams and thermodynamic properties of advanced nuclear fuels to meet the specialised requirements of the development of advanced fuels for future generations of nuclear reactors.

Specific technical objectives that this programme intends to achieve are to:

predict the solid, liquid and/or gas phases to be formed during fuel-cladding chemical interaction under normal and off-normal conditions
improve the control of experimental conditions during the fabrication of the fuel materials at high temperature, for example, by predicting the vapour pressures of the elements (particularly of plutonium and the minor actinides)
predict the evolution of the chemical composition of fuel under irradiation versus temperature and burn-up.

The project also identifies the need for and encourage the measurement of more experimental data.

The TAF-ID Phase 1 was established - from 2013 until 2017 - between 9 organisations of 6 NEA member countries: Canada (CNL, RMCC, UOIT), France (CEA), Japan (JAEA, CRIEPI), the Netherlands (NRG), the Republic of Korea (KAERI) and the United States (DoE).

The current phase (Phase 2) was established in November 2018 between 10 organisations from 6 NEA member countries: Canada (CNL, RMC, UOIT), European Commission (JRC- Karlsruhe) France (CEA), Japan (JAEA, CRIEPI), the Netherlands (TUD), the Republic of Korea (KAERI) and the United States (DoE) with an initial 3-year period

The control of the project is vested in the Programme Review Group (password protected | reminder), composed of members nominated by the signatories.

TAF-ID is co-ordinated by the NEA as a joint project and entirely funded by the signatories of the project.

The TAF-ID database will be generated and regularly updated by merging the existing databases and those being developed from the signatories of the project. The database will be available both in Thermo-Calc and FACTSAGE usable formats.

TAF-ID in development: working and public versions

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

A working version (access below) containing the description of all the systems to be investigated in the framework of the TAF-ID Project. This working version is currently accessible only to the signatories of the project. The version released in June 2020:

contains the following elements: Ag, Al, Am, Ar, B, Ba, C, Ca, Ce, Cr, Cs, Fe, Gd, H, He, I, La, Mg, Mo, N, Nb, Nd, Ni, Np, O, Pd, Pu, Re, Rh, Ru, Si, Sr, Ta, Te, Th, Ti, U, V, W, Zr
is used to model specific binary and ternary systems.

A public version (access below) 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, managed by the NEA, will be accessible to all NEA member countries upon request along with the signature of a non-disclosure agreement (NDA). The public version was available as of December 2014.

TAF-ID working version TAF-ID public version (password protected | reminder)