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Computational Fluid Dynamics (CFD) is widely used in different industrial applications. In this research, the application of CFD in the thermo-hydraulic evaluation for a typical small modular Pressurized Water Reactor (PWR) was studied using ANSYS Fluent software. First, reactor core with different (pitchfuel rod diameter) was simulated using MCNP code. Subsequently, axial neutron heat flux was calculated in the hottest rod. In the following, different fuel channels were simulated using ANSYS workbench and corresponding mass flow rate according to the fluid outlet temperature was computed using Fluent. Then, thermohydraulic parameters including pumping power, convective heat transfer coefficient and turbulent intensity were calculated. Artificial neural network (ANN) coupled with genetic algorithm (GA) was used for optimization; and pair pitch -fuel rod diameter (0.012 m, 0.0072 m) was selected as the optimum value. Also, Critical Heat Flux (CHF) was computed with CFD-simulation, and compared with Tong CHF correlation and Groeneveld look-up table. A good agreement was observed between results, but CHF obtained from CFD simulation was more conservative. According to the results, Minimum Departure from Nucleate Boiling Ratio (MDNBR) was obtained as 2.12, which was compatible with its typical value. Accordingly, it could be concluded that the optimum reactor core was in the safe mode in the steady state conditions.

Summary The main purpose of this paper was to review nanofluid applications as the main coolant of pressurized water reactors (PWRs) with both solid and dual‐cooled annular fuel. In this regard, first, theoretical and experimental models for calculating thermo‐physical properties of nanofluids including density, specific heat, thermal conductivity, viscosity, and heat transfer coefficient were reviewed and the effects of different variables such as particle volume concentration, particle size, shape, and temperature on these parameters were determined. In the following, research related to neutronic, thermal‐hydraulic, and safety investigations of nanofluids as the main coolant of PWRs with solid and dual‐cooled annular fuel were reviewed. Corresponding methods, codes, and results were discussed and compared. Based on studies, it was concluded that nanofluids' effects on key neutronic parameters (keff, neutron flux and radial and axial power peaking factor) depend on the used nanoparticle, volume concentration, and nanoparticle deposition on the cladding, while nanofluids can increase heat transfer, critical heat flux, and minimum departure from nuclear boiling ratio (MDNBR). Also, it was found that nanofluids with low volume concentration in reactor core with dual‐cooled annular fuel can replicate the same advantages. Furthermore, using dual‐cooled annular fuel instead of solid fuel increases MDNBR margin and reduces coolant flow which leads to a more compact design of the reactor core and a reduction of capital cost. Finally, incoming challenges and future works were presented.