S1W (Nautilus Prototype)

Overview

The Submarine Thermal Reactor Mark I (STR Mk1) project (later re-designated as S1W) was the first prototype naval reactor used to prove that the technology could be used for electricity generation and propulsion on submarines. Naval Reactors followed a concurrent design strategy, with the design and construction of the S1W reactor taking place ahead of the design and construction of the Nautilus, which would use the improved S2W Reactor and plant. This enabled problems to be identified and resolved before they appeared in the shipboard plant.

The land-based nuclear reactor was built at the Naval Reactors Facility (NRF) located at the National Reactor Testing Station, later called Idaho National Engineering Laboratory near Arco, Idaho.

The S1W was a pressurized water reactor (PWR) that utilized water as the coolant and neutron moderator in its primary system, and enriched Uranium-235 in its fuel elements. This approach was chosen based on the relative simplicity and inherent robustness of the reactor design approach relative to competing fission reactor plant concepts. The S1W reactor reached criticality on March 30, 1953. In May of that year, it began power operations, performing a 100-hour run that simulated a submerged voyage from the east coast of the United States to Ireland. In the mid-1960s, the S1W core was removed. An extension was bolted to the top of the reactor vessel so that a larger S5W reactor core could be installed. After that time, the prototype was called S1W/S5W.

The S1W/S5W plant was shut down permanently in 1989. The S1W deactivation and demolition (D&D) project is scheduled for completion in November 2025. (4)

All technical information is this overview is taken from reference (1) and (4) which are available from energy.gov.