The accurate modeling of nuclear reactors is essential for design, regulation, safety analysis, operations and forensic analysis. Geant4 as a framework for general computer simulation pf particle tracking in complex environments and materials. We have begun applying it to the case of modelling the neutronics in a nuclear reactor. In this link you can follow a recorded Ener-Connect Webinar delivered on behalf of our Group Modeling Pebble Bed Type High Temperature Gas Cooled Reactors Using Particle Transport Code.
The recorded presentation can be found here.
The powerpoint can be downloaded here.

Towards a Monte Carlo simulation of a pebble bed type high temperature gas cooled reactor using Geant4, A.C. Cilliers, S.H. Connell, J. Conradie, M.N.H. Cook, M. Laassiri, B.G. Maqabuka, R. Mudau, P. Naidoo, D. Nicholls, Annals of Nuclear Energy  168, (2022) 108868