S2W reactor

S2W reactor. The S2W reactor was a pressurized water reactor (PWR) designed and built by the Westinghouse Electric Corporation for the United States Navy. It served as the marine propulsion plant for the world's first nuclear-powered submarine, the USS Nautilus (SSN-571). The reactor's successful operation marked a pivotal advancement in naval technology and submerged endurance, fundamentally altering the strategic dynamics of the Cold War.

Design and development

The design and development of the S2W reactor was led by the Naval Reactors branch, overseen by then-Captain Hyman G. Rickover. The project was a cornerstone of the Atomic Energy Commission's naval reactor program, with detailed engineering executed by Westinghouse Electric Corporation at its Bettis Atomic Power Laboratory. The development drew heavily on earlier land-based prototype work, including the STR (Mark I) reactor at the Idaho National Laboratory. Key challenges involved miniaturizing a robust PWR system to fit within a submarine hull while ensuring exceptional reliability and safety under demanding operational conditions. The project proceeded under immense pressure due to competition with the Soviet Navy and was a direct technological response to advancements in Soviet submarine forces.

Description and specifications

The S2W was a two-loop pressurized water reactor system. Its core used enriched uranium fuel and was moderated and cooled by highly purified light water maintained under high pressure to prevent boiling. The primary coolant loop transferred heat from the reactor core to steam generators. There, a secondary loop of water was converted to steam, which drove the main turbines connected to the submarine's propellers through reduction gears. The plant also powered turbo-generators for electrical systems. The entire reactor plant and its associated shielding were contained within a compartment of the *Nautilus*'s pressure hull. The design emphasized simplicity and redundancy to achieve the unprecedented operational goal of prolonged submerged cruising without the need for atmospheric oxygen.

Operational history

The S2W reactor achieved initial criticality at the Idaho National Laboratory in early 1953 within the STR (Mark I) land-based prototype. After successful testing, the operational reactor plant was installed aboard the USS Nautilus (SSN-571), which was commissioned in September 1954. On January 17, 1955, the *Nautilus* signaled "Underway on nuclear power," a historic message to Naval Operations. The submarine shattered all previous endurance and speed records for submerged vessels, famously traveling over 1,300 miles submerged from New London, Connecticut to San Juan, Puerto Rico in 1955. The S2W plant reliably powered the *Nautilus* throughout its pioneering career, including the first submerged transit of the North Pole during Operation Sunshine in 1958. The reactor was refueled only once, in 1957, after logging over 62,000 miles. The success of the S2W plant directly validated the PWR concept for naval use and proved the strategic value of nuclear-powered submarines.

Variants and successors

The S2W design was the progenitor of the standardized S5W reactor, which became the United States Navy's workhorse naval reactor for decades, powering numerous classes including the *Skipjack*, *Thresher*, and *Sturgeon* classes. The S2W itself was a variant of the land-based STR and shared design lineage with the contemporary S1W reactor used in the prototype submarine at the Idaho National Laboratory. Direct evolutionary successors included the more powerful S3W reactor and S4W reactor plants developed for subsequent submarine classes. The technologies and operational principles proven by the S2W reactor formed the foundation for all subsequent generations of U.S. naval reactors, leading to advanced designs like the S6G reactor used in the *Los Angeles*-class and the modern S9G reactor of the *Virginia*-class.

See also

* Nuclear marine propulsion * Naval Reactors * Hyman G. Rickover * Pressurized water reactor * USS Nautilus (SSN-571) * S5W reactor * STR (Submarine Thermal Reactor) * Idaho National Laboratory * Westinghouse Electric Corporation

Category:Nuclear submarine reactors Category:Pressurized water reactors Category:United States Navy nuclear reactors Category:Westinghouse Electric Corporation