What is Pressurized Water Reactor?

A nuclear reactor that uses ordinary water under high pressure as both the coolant and neutron moderator, with a separate secondary steam loop to drive the turbine, representing the most widely deployed reactor type globally.

What category does Pressurized Water Reactor belong to?

Pressurized Water Reactor is a reactor-types concept in nuclear energy and SMR technology.

Pressurized Water Reactor — Nuclear & SMR Glossary

The Pressurized Water Reactor (PWR) is the dominant nuclear reactor type worldwide, accounting for approximately two-thirds of all operating commercial power reactors. In a PWR, ordinary (light) water serves dual roles as the neutron moderator, slowing fast neutrons to thermal energies where fission probability is highest, and as the primary coolant, carrying heat from the reactor core. The primary coolant loop operates at pressures of 150-160 bar to prevent boiling despite temperatures exceeding 300 degrees Celsius. Heat is transferred through steam generators to a secondary loop, where water boils to produce steam that drives the turbine-generator. This two-loop design keeps potentially radioactive primary coolant physically separated from the steam cycle, a safety advantage over single-loop boiling water reactor designs.

PWR technology is the foundation for the largest category of SMR designs. NuScale Power's VOYGR module (77 MWe per module, up to 924 MWe in a 12-module plant) is a natural-circulation PWR that eliminates reactor coolant pumps, enhancing passive safety. NuScale is the only SMR developer to receive NRC Design Certification (January 2023 for the 50 MWe US600, plus Standard Design Approval for the 77 MWe US460 in May 2025). Rolls-Royce SMR's 470 MWe design, selected as the UK's technology of choice and currently in GDA Step 3 with expected completion in August 2026, is a conventional PWR scaled for factory fabrication. Holtec International's SMR-300 (300 MWe) is a PWR with a partial construction permit application accepted by the NRC in February 2026, targeting twin units at the Palisades site in Michigan. Westinghouse's AP300 (330 MWe) is a scaled-down version of the licensed and operating AP1000.

Internationally, South Korea's KHNP i-SMR (170 MWe) and KAERI's SMART100 (100 MWe, which received Standard Design Approval from the NSSC in September 2024) are integrated PWR designs pursuing export markets. China's Linglong One (ACP100, 125 MWe), set for commercial operation in H1 2026, will be the world's first land-based commercial SMR and is a PWR design. GE-Hitachi's BWRX-300 and Last Energy's PWR-20 microreactor round out the light-water SMR field. The widespread operating experience, established fuel supply chain, and regulatory familiarity with PWR technology give these designs a deployment speed advantage, even as advanced coolant technologies pursue higher performance margins.