Extension of fission reaction model FIFRELIN for wider reaction conditions and post processing

Ogawa, Tatsuhiko   ; Litaize, O.*; Mancusi, D.*; Chebboubi, A.*; Serot, O.*

The Monte-Carlo code FIFRELIN was originally developed for the simulation of first chance fissions of fissile nuclei. In case of neutron-induced fissions, the compound nucleus always fissioned from an exited state whose excitation energy is sum of the incoming neutron energy and the neutron binding energy. While in the new version, with the multi-chance fission algorithm, the fissioning nuclei can start from higher exited states considering the competition of fission reactions, neutron emission, and gamma emission. When fission is selected in the competition, the partitioning of mass, charge, excitation energy, and angular momentum to the two fission fragments is determined either by the FIFRELIN native algorithm or by GEF. In fission reactions induced by energetic neutrons, pre-fission particle emission reduces the excitation energy of the compound nucleus before fission, leading to a noticeable difference of the final observables such as neutron multiplicity and fission product mass distribution. The other updated feature is the interface to codes handling the post-reaction processes. The energy spectra of neutrons, electrons and photons from fission reactions are output in a format compatible with PHITS, a general-purpose particle transport code. By using this functionality, one can simulate the transport and reactions of particles based on the cross section data and reaction models of PHITS, and the spectra calculated by FIFRELIN. Finally, the other interface developed in this study is nuclide yield output in a format compatible with DCHAIN-SP2014, a burn-up calculation code. This interface is necessary to consider the build-up, which depends on the time structure of the incoming neutron beam as well as the decay during the cooling period.