The accurate measurement of beta emitters is of utmost importance in various fields, including environmental monitoring, radiation protection and dismantling and decommissioning (D&D) operations. Nondestructive measurement techniques are crucial as they enable assessments of radioactivity without causing further harm or releasing additional hazardous materials. Due to the limited range of beta particles in matter, their characterization requires measurements in contact with the source term. In this paper, we present a study on the performance evaluation of a plastic scintillation detector designed for in-situ beta spectrometry measurements. The MCNP6.2 numerical model of the detector is detailed in the measurement configuration with beta, gamma and internal conversion electrons emitting sources. The calibration process and Gaussian Energy Broadening (GEB) parameters evaluation are discussed. Comparisons between the MCNP6.2 simulations and experimental measurements are exposed, both for gamma and beta spectra. While the gamma-ray detector response shows good agreement, greater discrepancies are observed in the beta ray response. To shed light on these discrepancies, a sensitivity analysis considering various sources of uncertainties is planned for future work.