Preserving the Past, Clearing the Future: Idaho Decommissions Naval Nuclear Prototypes

Today, these defueled prototypes are the focus of a large and complex environmental cleanup effort. Through a coordinated campaign led by the Department of Energy’s Office of Environmental Management, Idaho cleanup contractor Idaho Environmental Coalition (IEC), in partnership with the Naval Reactors (NR) program, the demolition and decommissioning of these facilities is not only reducing the legacy footprint and risk at NRF but also preserving the heritage of American naval innovation.

The path to demolition began in 2019 when NR and DOE-EM entered into an agreement for the department to carry out the D&D of the prototypes. It has continued through the rigorous regulatory process outlined by the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA).

In 2022, DOE-EM completed an engineering evaluation/cost analysis (EE/CA) for the planned D&D of the S1W and A1W prototype facilities. This process included reviews by the Environmental Protection Agency and the Idaho Department of Environmental Quality (DEQ), as well as input from the Shoshone-Bannock Tribe and the public on D&D alternatives. After public comment and technical review, DOE-EM and NR concluded that the complete demolition of the prototype facilities, including the removal of their respective reactor vessels and other support buildings, provided the best long-term solution to reducing risk.

In 2023, DOE-EM and NR signed an action memorandum to finalize this approach ,and the work on this historic project officially launched.

S1W: Demolition of a pioneer

On May 31, 2025, explosive charges were deployed to bring down the high bay facility over the S1W prototype.

To date, the most D&D progress has occurred at the S1W prototype project, where crews effectively dismantled the historically significant prototype that supported the development of the first nuclear submarine. Crews recently completed the safe demolition of the S1W prototype plant high bay—a 100-foot-tall building that housed the prototype—using explosives to carry out this key milestone.

The carefully planned demolition followed extensive efforts to safely remove contaminated and hazardous materials from the historic building. Earlier this year, D&D crews also removed the S1W prototype’s defueled reactor vessel, disposing of it in a nearby on-site disposal facility in accordance with federal and state regulations.

Over the summer months, IEC’s D&D team was to carefully manage and dispose of the debris, recycling to the extent practicable, before completing the project this fall.

A1W Prototype: Phased demolition

Meanwhile, crews have also advanced D&D of the A1W prototype facility. Initial efforts are focused on characterization of the facility and the removal of hazards like asbestos and polychlorinated biphenyl (PCB) used in building construction materials at the time. Ancillary buildings, such as a retention basin and a large steam condenser, have been dismantled to create space for future equipment staging.

With the S1W prototype project nearing completion, more resources, including staff, will be made available to advance the demolition of the A1W prototype.

S5G: Preparing the next chapter

Mark Brown, left, former manager of Idaho Cleanup Project, and Gil Pratt, manager of the Naval Reactors Idaho Branch Office, stand with a plaque commemorating the 30-year operational history of the S5G prototype.

The S5G prototype D&D project remains in the earliest phases of demolition. In October 2024, the S5G prototype was formally transferred to DOE-EM, and an EE/CA evaluation was conducted.

Unlike S1W and A1W prototypes, where construction started with a ground-level slab, the S5G prototype was housed in a below-grade pit requiring specialized demolition planning and a separate EE/CA.

DOE-EM and NR, with concurrence from the EPA and Idaho DEQ, are finalizing an action memorandum to outline the demolition plan for the S5G prototype. As outlined by the preferred plan, crews will remove hazardous materials and the S5G prototype before the basin, wherein the S5G prototype lies, is backfilled and closed. This plan aligns with the DOE’s commitment to greater efficiency, allowing for reduced environmental liability while also allowing the building to provide valuable space to support future work.

Innovative techniques, workforce strength, and environmental impact

Noncontaminated metals and debris are recycled to reduce the project’s environmental footprint.

Throughout the duration of the project, crews have maintained an accelerated pace while also upholding strict safety and environmental standards. This has been accomplished by a highly skilled workforce that has leveraged technology to achieve demolition success.

At the S1W prototype, crews restored a previously inoperable 125-ton overhead crane, allowing for the safe and cost-effective removal of large internal steel components. Dismantling the S1W prototype hull and shielding materials also required innovative techniques and a variety of tools to complete the demolition, such as diamond wire saws, plasma torches, reciprocating saws, and even electric chainsaws, highlighting the technical competency of the demolition team.

One of the most complex tasks involved the S1W prototype facility hot cell, a 7-ft-thick concrete structure that supported radioactive material handling during the prototype’s operational years. Originally slated for explosive delamination, crews instead successfully used excavators and hydraulic hammers, minimizing risk and environmental impact and also demonstrating a commitment to safety.

Removing the S1W prototype reactor vessel also proved to be challenging, as this effort was carefully coordinated with crews at the Idaho CERCLA Disposal Facility (ICDF), an on-site disposal facility for CERCLA waste streams generated on the INL Site.

The S1W prototype’s reactor vessel was buried in an on-site disposal facility in accordance with strict environmental regulations.

Beyond these technical achievements, IEC has emphasized environmental responsibility, which remains at the core of the D&D mission. All waste streams generated by the demolition are managed under strict CERCLA protocols. Noncontaminated materials are recycled wherever possible, and site activities are conducted with dust suppression, contamination control, and continual air-quality monitoring.

To date, more than 1,500 tons of material have been recycled, reducing the project’s environmental footprint. The project will continue recycling to the extent practicable through the demolition of the A1W and S5G prototypes. In addition, the ICDF maintains stringent waste acceptance criteria. The disposal facility is also equipped to contain hazardous material and ensure protection of Idaho’s natural resources.

Sponge blasting is an effective technique used by crews to remove hazardous materials from the A1W prototype facility.

The use of sponge-blasting technology at the A1W prototype to safely remove PCB-containing paint from metal components has also proven to be an environmentally beneficial innovation. This technology has not only reduced the volume of hazardous waste generated by the project, but it has also allowed metals to be recycled, contributing to DOE-EM’s mission to complete the safe cleanup of environmental legacy.

Labor force continuity has also been critical. Workers from completed D&D projects, like the site’s Accelerated Retrieval Project, have transitioned seamlessly into NRF demolition efforts, bringing with them valuable experience and expertise.

IEC’s approach has emphasized adaptability, with the team adjusting in real time to the demands of the project to safely and efficiently complete the work. Mike Swartz, IEC’s senior project director for D&D and capital projects, attributes the project’s success to the skill and determination of the crew performing the work.

“I am incredibly proud of our team and their ability to manage the demands of the project,” said Swartz. “Each milestone we reached is a reflection of their professionalism and a commitment to excellence.”

A historic legacy of nuclear innovation

The Submarine 1st Generation Westinghouse prototype facility after its construction in 1951.

The Aircraft Carrier 1st Generation Westinghouse prototype facility, located at the Naval Reactors Facility on the Idaho National Laboratory Site.

The Submarine 5th Generation Westinghouse prototype sits inside a below-grade hull, which was once filled with thousands of gallons of water to simulate ocean-like conditions.

Each of the three prototypes carries significant historical weight. The S1W prototype was the first land-based nuclear submarine prototype plant and is significant for its association with Adm. Hyman G. Rickover, the “Father of the Nuclear Navy.” The S1W prototype was built to simulate a submarine hull, with a nuclear reactor compartment surrounded by more than 300,000 gallons of water that mimicked ocean-like conditions. It supported the development of USS Nautilus (SSN 571), the world’s first operational nuclear-powered submarine.

In addition to providing critical research and development, the S1W prototype served as a training ground for more than 12,500 navy and civilian personnel, creating a skilled and competent force of naval nuclear operators.

In 1956, as the U.S. Navy’s need for nuclear-powered surface ships evolved, the A1W prototype construction began at the NRF. It contained two pressurized water reactors designed as prototypes for reactor plants to be used on surface ships. The A1W prototype began operations in 1958 and continued operations until January 1994, providing training opportunities for more than 14,500 navy and civilian students and was a testing ground for critical technologies, including those used in the first nuclear-powered aircraft carrier, USS Enterprise (CVN 65).

Constructed between 1961 and 1965, the S5G prototype was built to simulate the operations of a nuclear reactor within a submarine. During operations, it floated in thousands of gallons of water to mimic ocean-like conditions. The prototype was also used to train nearly 12,000 naval officers, enlisted personnel, and civilians to operate the propulsion plants of nuclear-powered submarines and ships. The S5G prototype was shut down in 1995 after 30 years of successful testing and training activities.

In recognition of their historical significance, NR and the Idaho State Historic Preservation Office are working together to preserve the legacy of these facilities through archived documentation, oral histories, and artifact collection. Many of these collections are preserved in the Library of Congress.

The demolition and decommissioning of the S1W, A1W, and S5G prototypes is a significant moment in INL Site history, marking an end of an era that contributed to the Naval Reactors Facility’s legacy of innovation. With every end comes an opportunity to chart a new legacy. DOE-EM and IEC have proven capable of completing this mission—combining cutting-edge technologies and demolition techniques with an unwavering commitment to ensuring the safety and health of the public.

Over the next several years, the project will demolish the last of these historic naval nuclear propulsion plants. Where these prototypes once stood, DOE-EM’s D&D work at NRF will stand as an example of technological excellence and environmental responsibility, ultimately preparing the INL Site for a safe and strong future. n

John “Carter” Harrison is a content strategist with Idaho Environmental Coalition.