Idaho National Laboratory (INL) has announced the approval of a new high-temperature metal to be an American Society of Mechanical Engineers (ASME) standard – and this bodes well for nuclear power plants. Alloy 617 is made up of a combination of nickel, chromium, cobalt and molybdenum, and can be used in tomorrow’s advanced nuclear plants because it allows higher temperature operation.
It took 12 years and a $15 million investment from the Department of Energy before the alloy could be added to the ASME Boiler and Pressure Vessel Code. ASME — which was established in 1880 and has grown to 100,000 members — is a globally-recognized, trusted source of standards used around the world.
According to the Lab’s announcement, the previously allowed high temperature materials could not be used above 750o C (around 1,380o F). However, the newly qualified material can be used in design and construction up to 950o C [about 1,750o F], which could enable new higher temperature concepts.
It is interesting that it’s just now recognized in ASME nuclear code as it offers superior metallurgical stability at 1100-1400F. So, why did it take so long to be approved? One of the Lab’s scientists explained that besides a long research and voting process, it was a matter of physical science:
“Regarding the physics…the issue has to do with creep – the tendency of a substance to change shape over time. Creep only becomes an issue starting at about half the melting point of a material. The lack of creep is why a car can sit in the driveway for years without the metal deforming.
But at higher temperatures, creep happens, and it will be a factor in new proposed reactors. Unlike light water reactors that operate at around 290o C (about 540o F), the proposed molten salt, high temperature, gas-cooled or sodium reactors will run two or more times hotter. So, determining what happens to Alloy 617 over time at a given temperature was critical.”
The scientist also explained that time-dependent properties can be “tricky” to measure and understand … and tests can take years.
Of course, manufacturers of Alloy 617 will have to make certain that the ‘recipe’ is correct and only alloys made to exact specification go out the door. This can be somewhat difficult, because with each new material innovation comes potentially greater products, but also a new list of analytical challenges. With the multitude of alloys being used in industry, confirmation of chemical composition using X-ray fluorescence (XRF) is a proven technology for the elemental analysis of specialty alloys to ensure the correct alloys are combined in the right percentages and the finished material meets precise manufacturing specifications.
I’ve seen this particular alloy in the field several times. In weld form, Inconel 617 is often used in high temp heater applications. It’s a neat material with a Ni base and Cr, Co, Ti, Al contributions and especially useful when joining Nickel alloys together: Inco 800HT, HP alloys, 25-35. The aluminum and chromium additions increase oxidation resistance at high temperatures; cobalt and molybdenum aid in solid-solution strengthening. So XRF technology can be key to helping ensure the material is made to spec.
Portable XRF analyzers are indispensable tools for helping to ensure that the right alloys are used in the correct percentages because even slight variations in the recipe can render the parts defective. (Read about how X-ray fluorescence (XRF) technology is increasingly being adopted to identify unknown materials and verify material composition throughout the automotive product development and manufacturing process.)
This is all good news for the nuclear power industry. According to the World Nuclear Association (WNA), about 55 power reactors are currently being constructed in 15 countries, notably China, India, Russia and the United Arab Emirates. Over 100 power reactors are on order or planned, and over 300 more are proposed. The WNA points out that most reactors currently planned are in the Asian region, with fast-growing economies and rapidly-rising electricity demand.
Again, according to the WNA, most nuclear power plants originally had a nominal design operating lifetime of 25 to 40 years, but engineering assessments have established that many can operate longer.
All the more reason to make sure creep is not an issue.