Modified point kinetic code for molten salt liquid fuel applied to the Thorizon One reactor

The molten salt reactor (MSR) is a concept whose feasibility was demonstrated in the 1960s with the Molten Salt Reactor Experiment (MSRE), which operated for five years at Oak Ridge National Laboratory (ORNL). Subsequently, research on this type of reactor slowed down due to a lack of investment, but recently interest in MSR has grown, with several startups around the world working on the development of this technology, which is recognised by the Generation IV International Forum (GIF). The aim of this work is to develop in Python a multiphysics code to perform point kinetic calculations and sensitivity analyses of relevant parameters of the Thorizon One reactor. Thorizon One is a cutting-edge MSR concept developed by the startup Thorizon. The developed model couples fuel flow and neutronics to help better understand the behaviour of the Thorizon One reactor in transient scenarios, studying its performance and providing support for reactor optimisation during the design phase. The developed code was verified by comparing its results with those of high-fidelity models applied to the Molten Salt Fast Reactor (MSFR) concept. The study on the Thorizon One focused primarily on transients due to Reactivity Initiated Accidents (RIA). During this type of transient, a strong negative reactivity feedback is rapidly triggered due to the Doppler effect and salt expansion. The latter effect acts on the same scale as the Doppler effect, since salt is assumed to be incompressible, a hypothesis justified by verification of compliance with a criterion. It has been found that reactor power peaks in RIA events are much more pronounced when the initial reactor power level is low. Furthermore, it is important to study reactor behaviour starting from low power levels and subjected to fuel-pump driven transients, such as pump start-up or pump shutdown, which cause a decrease and an increase in power, respectively. Finally, preliminary sensitivity results show that the impact of transit time through the core (and therefore its geometric dimensions) is significant during a RIA.