Abstract <p>Observable gamma-ray burst events can be caused by a multitude of different sources, leading to a wide diversity of observed spectra. This work examines a model linking long gamma-ray bursts and pair-instability supernovae. It is proposed that in the cores of such stars, characterized by high temperatures and low iron concentrations, the formation of electron-positron pairs during the final stages of stellar evolution destabilizes hydrostatic equilibrium, consequently leading to collapse. Within the model, it is assumed that gamma-ray burst emission arises through successive processes: Comptonization of cold stellar photons by a hot photosphere and relativistic beaming of scattered radiation, which forms the high-energy power-law component. Radiation trapping within the jet channel is also accounted for, leading to additional matter acceleration and spectral modification. The work employs a system of equations for relativistic radiation hydrodynamics with a constant gravitational potential, including the radiative transfer equation with scattering. A splitting scheme is proposed, solving the Radiative Transfer Equation (RTE) using the short-characteristics method, and the hydrodynamics using a Godunov-type method. The algorithm is designed for computation on cluster systems with graphics accelerators (GPUs). Simulations were performed modeling the acceleration of matter within a conical channel driven by radiation during a gamma-ray burst. The results demonstrate that during radiative acceleration, radiation trapping enhances radiation pressure due to the absence of photon energy leakage into the external environment. Furthermore, the relativistic nature of the flow causes the blackbody spectrum to shift into the gamma-ray range.</p>