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Welcome to the FISPACT-II Wiki. This platform serves as an online resource for code users and draws heavily from the User Manual and provides a comprehensive description of the code, keywords and physics, as well as tutorial examples. If you are interested in editing this wiki, please request an account through the FISPACT-II website contact page or FISPACT-II forum.

Please note that this wiki is limited to the content of the current released versions of FISPACT-II and not intended as a forum for discussion of development, bugs, code feedback, questions, etc -- for all of these there exists a FISPACT-II forum. For more general information, please visit the FISPACT-II homepage.


FISPACT-II is an enhanced multiphysics inventory and nuclear observables system providing a wide variety of advanced simulation methods and employing the most up-to-date and complete nuclear data for both neutron and charged-particle interactions.

FISPACT-II has been developed and is maintained by the United Kingdom Atomic Energy Authority at Culham. As a comprehensive, modern object-oriented Fortran code, FISPACT-II fully processes all ENDF-6 nuclear data including the complete TENDL data with full covariances files. Code features include self-shielding factors, broad temperature dependence, thin/thick target yields, robust pathway analysis, Monte-Carlo sensitivity and uncertainty quantification and propagation using full covariance data.

The latest generation of processing codes PREPRO, NJOY and CALENDF are used to provide the user with the most sophisticated incident-particle nuclear data from the TENDL-2017, HEIR-0.1, ENDF/B.VIII.0, JEFF-3.3, JENDL-4.0, and CENDL-3.1 international libraries, which are complemented with the latest decay and fission yield data, including the most recent GEFY-6.1 data. The maturity of modern, technological nuclear data including TENDL and GEF provides truly comprehensive data for all simulation requirements. The result is a multiphysics platform that can accommodate the needs of all nuclear applications including: activation, transmutation, depletion, burn-up, decays, source definition, full inventories, dpa, kerma, primary damage (PKA) spectra, gas/radionuclide production and more.

FISPACT-II v5.0 has now been release with a beta version API.

Quick links within FISPACT-II Wiki

External FISPACT-II related links

Release History

The code history is not comprehensive before release 3-00-00, but contains summaries of the major releases and details of the additions in the recent code versions. Since the code development is essentially linear and backwards compatibility is carefully maintained, users are encouraged to update to the most recent code distribution available.

Legacy version without support Former release without support Former supported release Current supported release Future release
Release history
Name Version Release Date Highlights Distribution
FISPACT-II 5.1 2023 This release has smaller solver tolerances by default to improve default accuracy, and it has a new Windows build process. UKAEA
FISPACT-II 5.0 coming soon (2021) This release will include an Application Programming Interface (API) (in beta phase) and new keywords to support the functionality of the compress_xs_endf and extract_xs_endf utility codes within the FISPACT-II itself. All new nuclear data libraries, including TENDL-2019 have been tested with this new version. UKAEA
FISPACT-II 4.0 Feb 2018 This release includes code extensions to handle high-energy (MF=10) nuclear data forms including the HEIR and HEAD libraries, the addition of non-neutron covariances for uncertainty propagation, addition of triton- and helion-induced simulation, new JSON output formats and various bug-fixes. The code now has regression testing, with automated builds tested on more than 100 operating system versions. The base Docker images used for tests can be found on the FISPACT-II Docker hub. Reference outputs for these systems can be found on the system_tests folder. All new nuclear data libraries, including TENDL-2017, JEFF-3.3 and ENDF/B-VIII were processed and tested with this new version. A new python package pypact for output parsing was also released. UKAEA, OECD-NEA DataBank, RSICC and commercial customers
FISPACT-II 3-20-00 Dec 2016 This code version includes the addition of several new, major features including enhanced energy-dependent fission yield treatment, depletion uncertainty, new graphical outputs, free gamma source discretisations, arbitrary incident particle energy groups, displacement damage energy threhsold modification, new incident-particle spectrum conversion algorithms, files file-less simulation and more. The keywords page highlights the new keywords with more detailed descriptions of their use. UKAEA and commercial customers
FISPACT-II 3-00-00 Oct 2015 This version marks the change to ENDF-format libraries as the default format for the nuclear data libraries, although capability to read EAF-2010 libraries is retained as an option. Fission yield processing has been updated: spontaneaous fission yields are now included, and the user can select either cumulative or instantaneous fission yield data. A POWER keyword has been introduced to allow fission power to be used to define the irradiating flux (for ENDF only). The processing of variance-covariance, uncertainty quantification and propagation has been improved. This release includes TENDL-2014, ENDFB-VII.1, JEFF-3.2 and JENDL 4.0u nuclear data libraries and the capability to read and process them. It can compress these to allow faster collapse calculations. The code can handle n, p, d, α and γ irradiation, There is a new interface module that allows inventories to computed for multiple flux spectra and returned to a calling program. There is also a separate Fispact MP program that allows inventory calculations to be performed for simulataneous irradiation by several different projectiles. UKAEA and commercial customers
FISPACT-II 2-00-00 The major change introduced in Release 2.0 of FISPACT-II was the addition of the reading and processing of alternative ENDF-format library data sets to meet the needs of the enhanced capabilities. This caused a major overhaul of the data input parts of the software and a huge expansion of the number of nuclides and reactions that can be treated; better fission yield data and cross-section data in more energy groups up to higher energies can now be used. This version can also handle more irradiating projectiles (γ, n, p, d, α) and provides additional diagnostic outputs (kerma, dpa and gas appm rates) if the ENDF-format library contains the required input data.

Features added in Release 2.10 are self-shielding using the universal sigmoid curve approximation, processing of covariances between different reactions, extended pathways analysis features, handling additional isomeric states and the capability to use the TENDL library data.

UKAEA, UK universities, European collaborators and commercial customers
FISPACT-II 1-00-00 This version began the process of extending the activation-transmutation prediction capability whilst maintaining the validation heritage of FISPACT-2007. New pathways and new monte-carlo sensitivity capabilities were introduced to extend both pathways and sensitivity calculations to multi-pulse irradiation cases. The reading and processing of CALENDF probability table data was introduced in the calculation of cross-section collapse to include self-shielding effects in the inventory calculations. UKAEA, UK universities, European collaborators and commercial customers
EASY-2010 2010, 2007 and previous These legacy versions of the code do not support ENDF-6 data and rely upon EAF data that is deprecated. Various other issues have been addressed in the re-development, including: use of an outdated ODE solution method, lack of rigorous uncertainty propagation and unsupportable software development process which results in numerous bugs without any foreseeable fix. Users are very strongly encouraged to make use of one of the modern releases. The legacy code versions have been distributed over the past 20 years to over 150 different establishments in 28 countries, including a 12 commercial licenses. Deprecated code.