nuclear milestone graphic
Alloy 617 high temperature creep test
High-temperature creep fatigue test on Alloy 617.
Idaho National Laboratory

For the first time in 30 years, a new metal has cracked “the code.”

The American Society of Mechanical Engineers recently added Alloy 617 into its Boiler and Pressure Vessel Code. The new addition is the sixth material cleared for use in high-temperature reactors and could allow new designs to operate at even higher temperatures.

The milestone ends a successful decade-long project by the U.S. Department of Energy (DOE) that consisted of researchers from Argonne, Oak Ridge and Idaho National Laboratories (INL).

“It’s a pretty substantial accomplishment,” said INL Project Manager Richard Wright. “This means designers working on new high-temperature nuclear plants now have 20% more options when it comes to component construction materials.”


Alloy 617 is a combination of nickel, chromium, cobalt and molybdenum. It was first developed for use in high-temperature gas reactors, but can also be applied to molten salt and liquid metal reactor designs.

Alloy 617 electron microscope image.
Electron microscope image of dislocation particle interaction in Alloy 617 put under stress at 750°C.
Idaho National Laboratory

The new metal offers significant improvements over previously approved alloys in the code and can withstand operating temperatures of 1,750◦ Fahrenheit—nearly 400 degrees hotter than the next-best material.

The expanded operating range gives advanced reactor developers more flexibility when choosing materials to build their high-temperature systems. The new designs could also open up new market opportunities for the nuclear industry by using its thermal heat to directly heat communities, drive industrial processes, produce hydrogen, and even purify water without emitting carbon.


Getting a new material into the code is a lengthy process and requires significant amounts of data. The national labs spent years testing the material properties of Alloy 617 in order to qualify the metal for commercial use.

Alloy 617 was added to the code in the fall of 2019 and is the first high-temperature material cleared for commercial use since the 1990s.

DOE invested $15 million over 12-years to make Alloy 617 available in support of the demonstration and deployment of advanced reactor concepts.

Learn more about the Office of Nuclear Energy and its work in developing new reactor technologies.

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