Thermal channel implementation in FissionIST

The Fission Reactor Simulator at Instituto Superior Tecnico (FissionIST) is an educational reactor ´ simulator designed to reproduce the behaviour of the Reator Portugues de Investigac¸ ˆ ao (RPI) based on ˜ a console interface. Previous work focused primarily on neutron kinetics and reactor instrumentation; however, the absence of the cooling systems prevented the simulator from accurately modelling power evolution.

This dissertation addresses that limitation through the implementation of a thermal channel module capable of simulating the reactor cooling circuits and their coupling with reactor kinetics. A dedicated Cooling Circuits Module was developed using a Raspberry Pi 5 integrated with analog and digital interfaces compatible with the existing simulator console.

The implemented software models the primary and secondary cooling circuits, including pump dynamics, heat exchanger behaviour, cooling tower heat rejection, and heat conduction within fuel assemblies. The system also introduces temperature-dependent reactivity feedback into the FissionIST neutronic simulation, enabling thermal and neutronic behaviour to evolve simultaneously during operation.

Simulation results demonstrated behaviour consistent with expected reactor operation under both steady-state and transient conditions. The implemented models reproduced coolant temperature evolution, flow coastdown dynamics, and temperature feedback effects, extending the realism and instructional capabilities of FissionIST while preserving compatibility with the original console-based architecture.