Within the framework of the dependable neutron ux instrumentation development for Sodium-cooled Fast Reactor (SFR) of Generation IV, the French Alternative Energies and Atomic Energy Commission (CEA) is investigating an innovative technology based on optical signals produced within an ionization chamber. In such gaseous detectors, neutrons interact with a ssile material, releasing heavy ions in the MeV-range, eventually leading to spontaneous photon emission in the ultraviolet to infrared range. In this paper, the process of light generation is analyzed through a newly-developed computer code named SCENA. Semi-empirical models for ion-togas energy exchange and secondary electron production are assessed. The output of the SCENA subroutines are satisfactory checked against other electron swarm simulation tools, experimental data and a theoretical gas model. SCENA is able to follow the cold-plasma created along a heavy ion slowing-down in space and time evolution. This performance is a key point in the development of optical ionization chambers.