Submarine Thermal Reactor

Submarine Thermal Reactor
Name	Submarine Thermal Reactor
Concept country	United States
Designed by	Naval Reactors branch
Manufacturer	General Electric, Westinghouse Electric Corporation
Reactor type	Pressurized water reactor
Status	Historical designation

Submarine Thermal Reactor (STR) was the United States Navy's pioneering designation for its first generation of naval nuclear propulsion plants, developed under the leadership of Hyman G. Rickover. This program, initiated in the late 1940s, successfully harnessed nuclear fission to provide submarines with a truly revolutionary capability: virtually unlimited underwater endurance and high speed, independent of atmospheric oxygen. The STR's success directly led to the operational USS Nautilus (SSN-571), fundamentally altering naval warfare and global strategic dynamics during the Cold War.

History and development

The program originated from research conducted by the United States Atomic Energy Commission and the United States Department of Defense, seeking a decisive advantage over the Soviet Navy. The project was spearheaded by the newly formed Naval Reactors branch, with Captain Hyman G. Rickover exercising unparalleled authority over its military and civilian aspects. The land-based prototype, designated S1W (Submarine, 1st generation, Westinghouse built), was constructed at the Idaho National Laboratory within the National Reactor Testing Station. Its successful operation in 1953 proved the viability of a compact, shielded pressurized water reactor for submarine use, paving the way for the installation of a nearly identical plant, the S2W reactor, aboard the USS Nautilus (SSN-571).

Design and operation

The core design was a pressurized water reactor, where water under high pressure served as both coolant and neutron moderator. This primary coolant loop transferred heat from the reactor core to a steam generator, where it produced steam in a secondary loop without becoming radioactive. This steam then drove turbines connected to the submarine's propellers and electric generators. Key innovations included extremely compact core design, robust radiation shielding using materials like lead and water, and systems for long-term operation without refueling. The entire reactor pressure vessel and primary loop were contained within a massive shielded reactor compartment.

Reactor types and models

The STR designation evolved into specific model codes indicating the manufacturer and platform. The prototype S1W reactor led to the production S2W reactor used on the USS Nautilus (SSN-571). Parallel development by General Electric produced the S1G reactor and S2G reactor prototypes at the Knolls Atomic Power Laboratory, exploring liquid metal cooled reactor technology. The successor to the STR series was the S5W reactor, which became the United States Navy's standard for decades, powering numerous classes including the *Skipjack*-class and *Thresher*-class. Later advancements included the S6G reactor for the *Los Angeles*-class and the S8G reactor for the *Ohio*-class.

Safety and containment systems

Safety was paramount, with multiple redundant and passive systems. The primary containment was the reactor compartment's pressure hull, designed to withstand internal accidents. Control rods, automatically inserted by SCRAM systems upon detection of anomalies, halted the nuclear chain reaction. Emergency core cooling systems could flood the core with borated water to ensure shutdown and remove decay heat. Extensive radiation protection measures protected the crew, with continuous monitoring by Geiger counters. Design principles emphasized simplicity and reliability, a philosophy enforced rigorously by Naval Reactors and later codified in standards by the Nuclear Regulatory Commission.

Decommissioning and waste management

Decommissioning of early STR plants followed protocols established by the United States Department of Energy and the Defense Nuclear Facilities Safety Board. The process involves defueling the reactor, removing the reactor compartment as a single, sealed segment, and transporting it via a specially designed barge to the Hanford Site or the Idaho National Laboratory for long-term storage. Spent nuclear fuel is handled as defense waste, initially stored in cooling pools before being transferred to secure dry cask storage facilities. The intact reactor compartments are buried in designated subsurface trenches, with their containment integrity monitored for environmental safety.

Role in naval propulsion

The STR's success rendered diesel-electric submarines strategically obsolete for many roles, creating the nuclear submarine and the ballistic missile submarine as central instruments of nuclear deterrence. It enabled the United States Navy to maintain continuous submerged patrols, particularly with the Polaris missile-armed *George Washington*-class. This technological leap triggered a naval arms race, prompting the Soviet Union to develop its own naval reactors through entities like the Kurchatov Institute. The principles proven by the STR remain foundational for all modern naval nuclear propulsion, including plants powering aircraft carriers like the USS *Enterprise* and the *Nimitz*-class.

Category:Nuclear naval propulsion Category:United States Navy reactors Category:Nuclear technology in the United States