The pressurized water reactor (PWR) is the dominant reactor type in the global nuclear fleet, powering roughly two-thirds of the world's operating nuclear plants. In a PWR, water is pressurized to about 155 atmospheres so it can be heated to over 300 degrees Celsius without boiling. This hot pressurized water transfers heat to a secondary loop through steam generators, where it produces the steam that drives electricity-generating turbines. The separation of primary and secondary loops adds a safety barrier between the radioactive coolant and the turbine system.
Several leading SMR designs are based on PWR technology, adapting proven principles to smaller, modular formats. NuScale Power's VOYGR uses natural circulation to cool a scaled-down PWR without the pumps required by large PWRs, enhancing passive safety. GE Hitachi's BWRX-300, while technically a boiling water reactor variant, shares many PWR heritage features. The Rolls-Royce SMR in the United Kingdom is designed as a 470 MW PWR intended for factory fabrication, targeting UK grid decarbonization.
The attraction of PWR-based SMRs lies in regulatory familiarity — licensing bodies like the NRC have decades of experience with PWR technology, potentially streamlining the approval process compared to more exotic reactor types. However, PWRs operate at lower temperatures than many advanced designs, limiting their applicability for industrial process heat. The established supply chain and operational knowledge base for PWR technology provide a practical advantage for near-term SMR deployment. For deeper coverage, see DeepTechIntel's nuclear section.