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FINIX (Package NEA-1901)


FINIX is a fuel behavior module that calculates the thermal and mechanical behavior of a nuclear fuel rod during steady-state and transient conditions. The temperature distribution in the fuel and cladding are solved coupled to the mechanical behavior of the pellet and cladding as well as the fuel rod internal pressure and fission gas release. Publicly available experimental correlations are used for the material properties, and simple models for the heat transfer from the cladding to the coolant have been included.

The intended use is the improvement of fuel behavior description in neutronics, thermal hydraulics and reactor dynamics codes. FINIX couples with the host code on a source code level, and provides an interface of functions that can be used to access the fuel behavior model from the host code. FINIX can also be used stand-alone with input files.


Non-commercial license

The NEA Data Bank offers a single-user license that does not include commercial applications. Please read the terms of the license carefully and refer to the VTT owners for more information.

Supplementary material

A collaborative repository with FINIX models for International Fuel Performance Experiments database is being established. These will be exclusively available to recipients of the database, which can be requested from the Data Bank. If you have any questions about how to contribute, please contact us.



H. Loukusa, J. Peltonen and V. Valtavirta. FINIX - Fuel behavior model and interface for multiphysics applications - Code documentation for version 1.19.12. Technical Report VTT-R-01109-19, VTT Technical Research Centre of Finland Ltd., 2019.


H. Loukusa, J. Peltonen, V. Valtavirta, V. Tulkki. Implementation of burnup effects in the multiphysics fuel behavior module FINIX. Annals of Nuclear Energy, 136, 107022, 2020, DOI:10.1016/j.anucene.2019.10702

A complete description of the project is found at the SERPENT website

Training materials

The NEA Data Bank has not hosted a training course on this software. If you are interested, please contact us.