The detailed modelling of the fuel-cladding system is of major importance for several studies related to safety improvement, lifetime extension for Generation II-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, up to the analysis of the fuel and cladding behaviour under severe accident conditions (pre-and post-fuel melting) and the interaction of corium with the vessel and sacrificial materials (in-vessel) and the concrete (ex-vessel).
These analyses may involve different types of fuel and cladding for Generation II-III and Generation IV systems:
One of the means of obtaining thermodynamic data of the chemical species of interest is by application of the CALPHAD method: this approach allows the calculation of phase diagrams (composition and number of the phases) over a large composition, temperature and pressure range as well as thermodynamic properties of these phases (heat capacity, enthalpy, activity, partial pressure, etc.) which stem 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 prior to the modelling phase of the chemical species of interest.
Currently, several tools are used in various laboratories and organisations which are part of the OECD-NEA:
Each of these databases allows performing studies on only a few of the chemical species described above. The unification of these separate databases would 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 validation of its database.
The OECD-NEA Thermodynamics of Advanced Fuels - International Database Project was established in 2013 to make available a comprehensive, internationally recognised and quality-assured database of phase diagrams and thermodynamic properties of advanced nuclear fuels with a view to meeting the specialised requirements for the development of advanced fuels for a future generation of nuclear reactors.
Specific technical objectives that this programme intends to achieve are to:
The Project will also identify the need for and encourage the measurement of further experimental data.
This joint Project was established between nine organisations of six 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), with an initial 3-year period.
The control of the Project is vested to a Programme Review Group, composed by members nominated by the Signatories.
TAF-ID is co-ordinated by the OECD-NEA, as a joint Project, 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.
Two versions of the TAF-ID database are being developed:
Last reviewed: 10 July 2017