ATR employs a unique design in which key internal components can be completely replaced during a core overhaul every 10 years on average to enable long-term operations. This overhaul is called a Core Internals Changeout. ATR is undergoing its sixth core overhaul during 2021, and more details are available in the links on this page.

Numerous other upgrades and improvements have been done since ATR entered service in 1967. The Department of Energy is continuing to invest in infrastructure upgrades on the reactor and key plant facilities to ensure ATR can continue to serve the nation’s needs for decades to come.

This planning includes the procurement and availability of critical spare parts, including one-of-a-kind components such as core internal components and beryllium reflectors. Planning also addresses staffing requirements and identifies the funding, schedule and prioritization for replacing key components and systems.

ATR’s capabilities and infrastructure are accessible through various programs that support the U.S. and international nuclear research efforts. ATR is the only U.S. research reactor capable of providing large-volume, high-flux thermal neutron irradiation in a prototype environment. The reactor’s singular design makes it possible to study the effects of intense neutron and gamma radiation on reactor materials and fuels.

National Security

Over the years, ATR has provided vital irradiation testing capability supporting the U.S. Navy’s nuclear propulsion program. The Navy remains a key customer of ATR and testing has contributed to the exceptional operational performance of the nuclear-powered fleet.

Nuclear Energy 

Experiments conducted at ATR provide a critical look at reactor components and systems. Testing at ATR supports reactor research around the world to extend the life of current nuclear power plants, develop designs for advanced reactors, and test new types of stronger nuclear fuels that reduce waste generation and proliferation risks.

Collaborative Research

ATR’s capabilities are an essential part of efforts to support nuclear energy research and development in the U.S. and around the world. ATR capabilities are accessible to universities, industry and international partners through DOE’s Nuclear Science User Facilities, the Gateway for Accelerated Innovation in Nuclear, and the National Reactor Innovation Center, as well as other research partnerships. ATR’s capabilities are also key to INL’s certification to the International Atomic Energy Agency (IAEA) International Center of Excellence based on Research Reactors (ICERR) standard.

Isotope Production

ATR is the only U.S. source of the valuable medical grade cobalt-60 isotope needed for “gamma knife” therapy used to treat brain tumors, and produces plutonium-238 for NASA’s deep space exploration missions.

Advanced Test Reactor, ATR, Cherenkov Effect, nuclear reactor, inside of nuclear reactor


Celebrating 50 years of ATR and counting

2017 was a banner year for INL’s Advanced Test Reactor, marking 50 years of operation for one of the most innovative, flexible and durable scientific research tools ever built. The reactor was designed by Deslonde de Boisblanc in 1959.

At its groundbreaking ceremony in 1961, Idaho Gov. Robert E. Smylie said the $40 million project was the largest construction project in the history of the state. It began operating in 1967. Celebrations to honor the reactor’s 50-year anniversary were held in June 2017. ATR leadership and dignitaries across the state recognized the occasion.

Advanced Test Reactor, ATR, Cherenkov Effect, nuclear reactor, inside of nuclear reactor