INL begins overhaul of US test reactor

ATR is a pressurised water reactor which is used to produce neutrons, rather than heat, and operates at lower pressures and temperatures than a large commercial nuclear power plant. The neutrons are concentrated in the reactor's core by a beryllium reflector and used to test nuclear fuels and materials in support of missions for the US Navy and the US Department of Energy's (DOE) Office of Nuclear Energy. Its research capabilities are also available to universities, industry and international partners through initiatives including the 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. In addition, the reactor is the only US source of medical-grade cobalt-60 for "gamma knife" therapy and produces plutonium-238 for NASA's deep space exploration missions.

The high levels of neutrons in the reactor's core will eventually degrade the beryllium reflector and other core components, so the reactor is designed to enable replacement of its key internal components through a process known as core changeout. This was last done in 2004. The latest overhaul, which began in April, will take about nine months to complete, with reactor operations expected to resume in early 2022.

ATR's unique cloverleaf core design makes it possible to conduct multiple simultaneous experiments under different test conditions. "Even today, more than 50 years after the reactor came online, no other test reactor can match its versatility," INL said.

The core changeout process will include the removal and replacement of much of ATR's experiment support infrastructure, including the tubes that are used to expose experiments to the core environment. The 23 interlocking concrete and steel shield blocks that rest over the reactor vessel during normal operations will be removed before the 62,000-pound (28 tonne) stainless steel reactor vessel lid is removed for inspection and upgrades. The reactor's reflector blocks and other key components will then be replaced before reassembly and the reinstallation of the experiment infrastructure.

A video providing an animated overview of the core changeout process can be seen here.