• startup
• natural circulation
• integral pressurized water reactor
• helical coil steam generators
• passive safety systems
• system codes
• thermal hydraulics
• i-PWR
• RELAP5
• station black out

This work offers a comprehensive review of integral Pressurized Water Reactors (iPWRs), highlighting their key characteristics. Additionally, it provides an overview of several innovative designs such as CAREM, IRIS, SMART, and NuScale, all of which feature Helical Coil Steam Generators (HCSGs). The thermal hydraulic design aspects of these heat exchangers, including relevant correlations and modeling approaches within system codes, are discussed in detail. Furthermore, the thesis delves into the application of system codes, with a particular focus on RELAP5, and explores fundamental principles of nuclear safety analysis. Lastly, the paper presents a RELAP5-3D nodalization tailored for an iPWR operating in natural circulation, covering aspects such as steady-state and startup scenarios in natural circulation, the potential for power uprate in forced circulation, and sensitivity studies on a Station Blackout Scenario (SBO).