In JET pulse 95135, a runaway electron (RE) beam was intentionally created by means of an argon (Ar) massive gas injection (MGI) which triggered a disruption. A D2 shattered pellet injection into the beam was then performed, leading to its benign termination (C. Reux et al., Phys. Rev. Lett. 126 [2021] 175001). The RE termination phase has been studied with JOREK (V. Bandaru et al., Plasma Phys. Control. Fusion 63 [2021] 035024) and these studies are being pursued. However, here, we do not study the termination of the beam but its generation following the Ar-MGI-triggered disruption, which has been studied already with GO and DREAM (A. Järvinen, J. Plasma Phys. 88 [2022] 905880612). At this stage, we use 2D axisymmetric simulations, tuning some parameters (transport coefficients, Ar source) in an ad hoc way in order to obtain a reasonable agreement with experimental observations, e.g. regarding the current quench timescale. We then assess RE generation with the RE fluid model of JOREK or with a test particle approach.