Disruptions, i.e. major instabilities in which plasma confinement is lost, are a significant threat to tokamak operation not only because of the large in vessel forces involved, but also because they may lead to the acceleration of some electrons to relativistic speeds. These so-called runaway electrons (REs) can exponentially multiply due to large-angle collisions with thermal electrons during the RE avalanche. As the RE avalanche is exponentially sensitive to the pre-disruption plasma current, this can lead to multi-MA RE beams in large future devices which may cause severe localized wall damage. Therefore, simulations including the RE sources in realistic 3D fields are needed to further the understanding of RE generation and losses and develop viable mitigation scenarios. The 3D nonlinear MHD code JOREK [^1] contains a hybrid fluid-kinetic model that describes the REs with a full-f relativistic particle in cell (PiC) approach using either full-orbit [^2] or drift kinetic RE descriptions [^3]. In this contribution, the implementation of the relativistic large-angle collision operator that makes up the avalanche source is presented, along with a resampling technique that’s needed to limit the number of markers [^4]. A first application of the avalanche source to a beam termination scenario is shown as well. Plans for future applications will be shortly discussed and include simulating a beam termination-reformation cycle. To efficiently cross long time scales with high resolutions, current work by Edoardo Carrà et al. is focusing on porting the computationally expensive kinetic models to GPU’s [^5]. [^1]: M. Hoelzl, G.T.A. Huijsmans et al. The JOREK non-linear extended MHD code and applications to large-scale instabilities and their control in magnetically confined fusion plasmas. *Nuclear Fusion*, 61(6), 2021. [DOI 10.1088/1741-4326/abf99f](https://iopscience.iop.org/article/10.1088/1741-4326/abf99f) [^2]: H. Bergström, S-J Liu et al. Introduction of a 3D global non-linear full-f particle-in-cell model for runaway electrons in JOREK. *Plasma Physics and Controlled Fusion*, 67(3):035004, 2025.[DOI 10.1088/1361-6587/adaee7](https://iopscience.iop.org/article/10.1088/1361-6587/adaee7) [^3]: S. Liu, T. Liu et al. Hybrid fluid–kinetic simulations of resistive instabilities in runaway electron beams. *Journal of Plasma Physics*, 92(1):E3, 2026. [DOI 10.1017/S0022377825101025](https://www.cambridge.org/core/journals/journal-of-plasma-physics/article/hybrid-fluidkinetic-simulations-of-resistive-instabilities-in-runaway-electron-beams/E5895F7B730FABBCF3A0A5DDF6978DD6) [^4]: F. Wouters. Implementation and validation of the avalanche source for a 3D kinetic model of relativistic electrons during disruptions. [Master's thesis](https://research.tue.nl/en/studentTheses/implementation-and-validation-of-the-avalanche-source-for-a-3d-ki/), Technical University of Eindhoven, June 2024. [^5]: E. Carrà, P. Rác et al. GPU Acceleration of Hybrid Fluid-Kinetic Simulations of Runaway Electrons in JOREK. *Poster at: DPG Erlangen*, 2026.