About the IRSN Mephista-20 Nuclear Fuels Database (MEPH20)

IRSN Mephista-20 Nuclear Fuels Database (MEPH20) is a thermodynamic database, owned by IRSN, which can be applied to successfully study fundamental scientific issues and efficiently investigate practical engineering problems in new generation nuclear fuels. It effectively allows you to calculate the thermochemical equilibrium states in nuclear fuels and to utilize the calculation results for enhancing the design and engineering of modern and safety-prioritized nuclear reactors, improving the predictions and treatments of operational accidents and assisting the assessment and processing of nuclear fuel and waste managements.

The database contains critically-assessed and internally-consistent thermodynamic data for the entire field from metal to oxide domains within a 15-element framework, +H and +Ar, which are only for the gaseous phase and for hydrides and hydrous oxides/silicates.

MEPH: IRSN Mephista Nuclear Fuels Database Revision History. The current version of the database is MEPH20.

Elements (15+2)

Ar	Ba	C	Ce	Cr	Cs	Fe	H	La	Mo
O	Pu	Ru	Si	Sr	U	Zr

Phases and Assessed Subsystems

See the included standalone PDF, Overview of Mephista-20, that has details such as atoms, stoichiometric condensed phases, condensed solutions, gas, and the assessed binary, ternary, and quaternary systems.

Available Solution and Stoichiometric Phases

Condensed solution phases: (solid/liquid phases)	51 phases
Condensed stoichiometric phases: (solid/liquid substances)	263 phases
Gaseous mixture phase: (ideal gaseous mixture)	165 gaseous species

The hydrogen element (H) being as a major component is added into the system, while its dissolution in condensed solid and liquid solution phases has not been taken into account yet. The Ar component is only present in the gaseous mixture phase. Included condensed stoichiometric phases (pure substances) are widely ranged: intermediate metallic compounds, oxides and hydroxides, silicates and hydrous silicates, hydrides, carbides and carbonates, and some simple inorganic/organic substances.

Available Assessments and Evaluations

Binary subsystems: (metallic alloys, carbides, oxides)	105
Ternary subsystems: (metallic alloys, carbides, oxides, silicates)	61
Quaternary subsystems: (oxides, silicates)	2

For many other ternary, quaternary, and higher-order subsystems, the analytical descriptions of lower-order constituent subsystems are effectively combined and used (through appropriate extrapolations) to predict multicomponent systems, especially for compositions and temperatures which have not been experimentally evaluated. Depending on the complexity of multicomponent systems, such an analytical prediction will be more or less accurate.

Limits

As in the spirit of the CALPHAD method, predictions can be made for multicomponent systems by extrapolation into multicomponent space of data critically evaluated and assessed based on binary, ternary and in some cases higher order systems. However, critical calculations must always be verified by equilibrium experimental data; it is the user's responsibility to verify the calculations but Thermo‑Calc Software AB is interested to know about any significant deviations in order to improve any future release.

Additional Resources

This document is available on our website on the Nuclear Materials Databases page, where you can also link to many other resources. Alternatively, when in Thermo‑Calc, press F1 to search the online help for more information.