Molten salt reactors (MSRs) offer promising prospects for advanced nuclear energy due to their high efficiency and inherent safety features. Ni-Cr alloys, such as Hastelloy N, are prime candidates for structural components owing to their excellent corrosion resistance in molten fluoride salts. However, a critical challenge arises from fission products like tellurium ($Te$), which is produced via uranium fission and migrates to alloy grain boundaries. There, Te reacts with chromium ($Cr$) to form brittle telluride phases (e.g., $\text{Cr}_2\text{Te}_3$ and $\text{Cr}_3\text{Te}_4$), leading to intergranular cracking and premature material failure under irradiation and high-temperature conditions. Understanding the evolution of telluride microstructures---nucleation sites, precipitate morphology, size distribution, and spatial arrangement---is essential for mitigating this degradation and enabling long-term MSR deployment.This study employs phase-field modeling to predict the three-dimensional (3D) microstructure development of telluride precipitates in Ni-Cr alloys during MSR operation. The model integrates multi-phase, multi-component thermodynamics using the CALPHAD (CALculation of PHAse Diagrams) framework, coupled with multicomponent diffusion kinetics described by the Darken equation and interface mobilities calibrated from diffusion couple experiments. Key physical phenomena captured include: (1) heterogeneous nucleation at grain boundaries driven by Te supersaturation and Te grain boundary diffusion, (2) competitive growth between Cr-rich and Ni-Te phases under varying Te chemical potentials, and (3) elastic strain energy from lattice mismatch. The simulations were performed under the isothermal conditions at $700^\circ\text{C}$ with Te influx rates informed by MSR neutronic condition ($\sim 10^{16}$ Te atoms/$\text{m}^2\cdot\text{s}$). Simulations reveal that telluride precipitates initially nucleate as wedge-shaped particles at triple junctions, evolving into interconnected networks along grain boundaries within hours. Coarsening follows a Lifshitz-Slyozov-Wagner-like mechanism, with average particle sizes reaching 1--5 $\mu\text{m}$ after 1000 hours, promoting crack initiation paths. Sensitivity analyses highlight the dominant role of grain boundary segregation energy ($\sim 0.5$ eV) and Te diffusivity ($D_{Te} \approx 10^{-14}$ $\text{m}^2/\text{s}$) in dictating morphology. Alloying with elements like Nb or Mo is predicted to suppress nucleation