Fuel behavior modelling with molecular dynamics and thermodynamic modelling

by Dr Sergii Nichenko (PSI - Paul Scherrer Institut)

Thursday 5 Nov 2020, 14:00 → 15:00 Europe/Zurich

Zoom ID: 293 245 8409 / PC: 874052

In recent decades, the application of modelling tools in a field of nuclear research witnessed a significant surge. Such tools, like Density Functional Theory (DFT), Molecular Dynamics (MD), Thermodynamic modelling, Force Field modelling, etc., could provide answers to questions like fuet behavior, thermodynamic and physical properties of different types of fuels at different conditions and fission products (FP) release behavior under accident conditions just to name a few.

The presented research is focused mainly on two areas: (1) Thermodynamic properties of Molten Salt Reactor (MSR) related multicomponent systems and (2) nuclear fuel and FP behavior under normal and accident conditions. To tackle different challenges and questions in my research two modelling approaches are used complementarily: Molecular Dynamics and Thermodynamic modelling.

MD modelling, using the AMoDy code, is used in my research to provide information on dynamic physical properties of solid fuels LWR, as well as molten salt systems used in MSR. It is, however, not always a simple and straightforward task to calculate dynamic properties of materials with classical MD or to fit Force Field parameters to be able to model complex crystal structures, as those observed, e.g., in ThF4 system. Therefore, a significant part of my research is dedicated to the development of MD algorithms for improved properties calculations as well as improvement of Force Field models.

Thermodynamic modelling, with the GEMS thermodynamic package, as a tool is a significant asset that helps us answer and better understand such questions as FP behavior, chemical speciation in the MSR, phase equilibria in complex multicomponent systems, and more. In my research Thermodynamic modelling is used to shed light on the FP and salt compounds release behavior from a molten salt reactor fuel as well as from the solid nuclear fuel under severe accident, speciation in the molten pool and solid fuel as well as in the gas phase, and so forth. Thermodynamic modelling (GEMS), however, is not enough by itself to investigate the FP release behavior since it provides the with information on the speciation and thermodynamic properties of different species at equilibrium conditions. To extend the research scope outside equilibrium thermodynamic modelling the GEMS packages had to be coupled with the integral severe accident modelling code MELCOR, which itself has limited thermodynamic modelling capabilities. The developed coupling interface, cGEMS, is used to investigate the vaporization of salt and fission product species from the MSR fuel in accident conditions as well as an improved thermodynamic description of the fission product release from the nuclear fuel under severe accident conditions.

As it can be seen, in the presented research modelling tools are not only being used to tackle research problems but are as well being developed and coupled to complement strengths of one modelling tools with the capabilities of others in an effort to study mode complex and interesting problems.