BOISE, Idaho -- Scientists at the Idaho National Laboratory have completed a rare overhaul of one of the world’s most powerful nuclear test reactors and normal operations are expected to resume later this spring, officials said Monday.

The 11-month outage at the U.S. Department of Energy's Advanced Test Reactor, or ATR, in eastern Idaho allowed a core overhaul that's done, on average, about every 10 years. The changeout was the sixth since the reactor started operating in 1967 and the first in 17 years.. //

The ATR is unique because unlike commercial nuclear reactors that produce heat that’s turned into energy, the ATR produces neutrons so that new materials and fuels can be tested to see how they react in high-radiation environments. The test reactor’s unique cloverleaf design includes a core that’s surrounded by beryllium metal to reflect the neutrons.

But all those neutrons put wear on the internal parts of the test reactor, meaning it would lose the ability to conduct experiments if it is not refurbished.

The reactor’s designers foresaw that problem and created a reactor with internal components that can be periodically replaced.