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Advanced Test Reactor_Core
Photo courtesy of Idaho National Laboratory

Idaho National Laboratory (INL) recently completed the sixth major core overhaul of the Advanced Test Reactor (ATR).

ATR is the world’s most powerful test reactor and provides unmatched experimental capabilities and versatility. Its unique design allows for multiple experiments to be conducted simultaneously, under different testing (power, temperature, coolant, and chemistry) conditions.

Now that the core overhaul is complete, ATR enters a 50-day testing and measurement phase to calibrate new instruments and sensors for the reactor’s control systems and experiment loops. ATR is expected to resume normal operations by late spring to test nuclear fuels and materials for the U.S. Department of Energy (DOE), the Navy’s nuclear propulsion program, industry, and researchers from universities.

Core Internals Changeout

ATR shut down in April 2021 to begin the overhaul called a Core Internals Changeout (CIC)–– a process that replaces and updates internal reactor components. This is ATR’s sixth core overhaul since it began operation in 1967. The overhaul process occurs approximately every 10 years and consists of three phases: accessing the reactor core by removing the reactor vessel head, removing the main core components, and installing new components. The replacement reactor components must be precisely aligned during installation to ensure proper operation of fuel and reactor safety systems.

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The Advanced Test Reactor at Idaho National Laboratory undergoes an overhaul called a Core Internals Changeout to replace the reactor’s key core components, which occurs about every 10 years on average.
Video courtesy of INL

As a nuclear materials test reactor, ATR generates very high levels of neutron irradiation that causes strain or microscopic damage to internal components, particularly its beryllium reflectors–– which help concentrate neutrons on the fuels and materials being tested. The CIC overhaul allows for the replacement of components that endure the most wear and tear during routine operation. The entire process restores the main ATR core components as well as non-reactor components and systems to a like-new condition.

 “I am immensely proud of the ATR workforce and their exceptional performance throughout the core overhaul outage,” said Sean O’Kelly, Associate Lab Director of the ATR Complex at Idaho National Laboratory. “From planning to execution and then dealing with the inevitable unexpected challenges that arose during the last 10 months, they’ve displayed an amazing degree of professionalism, teamwork, and adaptability to get us back in operation and performing our important mission as soon as possible.”

The reactor is used to perform irradiation testing of many nuclear materials and fuels that support a wide range of goals, including the U.S. Navy’s nuclear-powered fleet, the development of accident tolerant fuels, advanced fuels for small modular reactors and microreactors, and production of Plutonium-238 for future NASA deep-space missions.

Learn more facts about ATR here.