Nanosecond discharges are characterized by a shift in energy branching toward the excitation of electronic levels and dissociation, making them particularly attractive for plasma chemistry. Understanding the spatiotemporal structure of these discharges is especially important. This paper presents a detailed 2D-axisymmetric numerical analysis of a nanosecond discharge propagating in a long tube and in pure nitrogen. The modeling is conducted using a self-consistent plasma fluid solver under the local mean energy approximation (LMEA), including photoionization. The discharge develops at moderate pressures, 1 - 10 Torr, in the form of a fast ionization wave (FIW). Simulations are performed for both negative and positive polarities of the voltage pulse applied to the high-voltage electrode. The computational results are validated against available experimental data, including FIW velocity within the studied pressure range, electron density, longitudinal electric field, and the radial distribution of N2(C) emission on a nanosecond timescale.